Class 8

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 10 Not For Drinking-Not For Breathing

AP State Syllabus 8th Class Biology Important Questions 10th Lesson Not For Drinking-Not For Breathing

8th Class Biology 10th Lesson Not For Drinking-Not For Breathing 1 Mark Important Questions and Answers

Question 1.
Which department issues the pollution under control certificate?
Answer:
The pollution check up centre issues the certificate.

Question 2.
For how much time is it valid?
Answer:
It is valid for six months.

Question 3.
For which types of vehicles has it been issued?
Answer:
All types of vehicles like motor bike, scooter, car, bus, lorry etc.

Question 4.
What is emission test?
Answer:
The test conducting of the gases releasing from the vehicle is called emission test.

Question 5.
What components are tested in the pollution check up centre?
Answer:
Carbon dioxide, carbon monoxide, nitrogen, hydrocarbons, sulphur dioxide etc.

Question 6.
What will happen if harmful microorganisms or substances enter your body? How do you feel?
Answer:
If harmful microorganism enter the body the normal functioning of the body will be disrupted or disturbed. We feel sick.

Question 7.
What is the effect of rapid increase in the number of vehicles?
Answer:
With the number of vehicles increase, the pollution also increases, which causes air pollution.

Question 8.
What is pollution?
Answer:
Anything that is harmful to the environment is called pollution.

Question 9.
When do all the living organisms with in the environment will be healthy and thriving?
Answer:
When everything is working the way it should be all the living organisms with the environment including humans are healthy and thriving.

Question 10.
Name the diseases caused by air pollution.
Answer:
Diseases of the respiratory system like lung cancer, Asthma etc.

Question 11.
What do our elders talk about the environment?
Answer:
Our elders talk about the blue sky, clean water and fresh air that was available in their times.

Question 12.
What is our environment made up of?
Answer:
The environment is made up of systems, cycles and specialized relationships between living and non – living elements.

Question 13.
Name some substances which impact the health of our earth.
Answer:
Litter, car exhaust, motor oil, used tires, smoke, chemicals, disposed computer, mobile phone material etc., all of these can have an instant or a gradual impact on the health of our earth.

Question 14.
What are the four major gases in the air?
Answer:
The four major gases are nitrogen, oxygen, argon and carbondioxide.

Question 15.
Which is the essential element for survival of all living organisms?
Answer:
The atmosphere contains 21 % of oxygen which is essential for survival of all living organisms.

Question 16.
How is carbon dioxide important?
Answer:
Carbon dioxide which is 0.033% is essential for the process of photosynthesis in plants.

Question 17.
What is air pollution?
Answer:
The contamination of air by impurities which may have harmful impacts on the living organisms and the non-living components of the environment is called air pollution.

Question 18.
What are pollutants?
Answer:
Pollutants are the substances which contaminate the environment.

Question 19.
Name the main pollutants in the atmosphere.
Answer:
Suspended particulate matter, carbondioxide, carbon monoxide, oxides of sulphur and nitrogen CFCs and heavy metals.

Question 20.
Name the natural disasters in the world.
Answer:
The natural disasters in the world are volcanic eruptions, forest fires and sand storms which leads to air pollution.

Question 21.
What is the problem with airborne pollutants?
Answer:
The problem with airborne – pollutants is the way winds criss – cross the globe, picking up pollutants and carrying them all over the world. Air pollution is not just a local concern.

Question 22.
What pollutants are released by forest fires?
Answer:
Forest fires release carbon particles (ash) into the air and pollute the air.

Question 23.
What gas is released from decay of organic matter?
Answer:
Decay of organic matter releases Ammonia gas into air.

Question 24.
What gas is released from decay of organic matter lying under water?
Answer:
Decay of organic matter lying under water releases Methane gas as air pollution.

Question 25.
How do pollen grains pollute the air?
Answer:
Pollen grains released by plants remain floating in the air and pollute it.

Question 26.
What gases are produced by burning fuels?
Answer:
Burning fuels pollute the air by producing carbon – monoxide, sulphur dioxide, smoke, soot and ash.

Question 27.
What gases are emitted by vehicles?
Answer:
Sulphur dioxide, nitrogen dioxide, carbon monoxide, unburnt hydrocarbons, lead compounds and soot.

Question 28.
Name the polluted areas and the factories present in that area.
Answer:

1. Prakasam district – Granite factory
2. Macharla – Cement factory
3. Piduguralla – Lime stone

Question 29.
Name various industries that pollute the air.
Answer:
Granite, lime, cement factories pollute the air by releasing sulphur dioxide, nitrous oxide, chlorine fly ash, dust, asbestos dust etc.

Question 30.
How local people are suffering living near Parawada and Krishnapatnam Thermal Power Plants?
Answer:
The Thermal power plants release fly ash, sulphur dioxide and radio active substances into air, water and land, local people are suffering from lung cancer and skin allergies.

Question 31.
What are the problems face by the people living near the granite factory?
Answer:
The people living near the granite factory are facing several health problems like respiratory bronchitis and asthma.

Question 32.
How are Nuclear power plants dangerous?
Answer:
The two problems of Nuclear power plants are radio active waste and melt downs.

Question 33.
What are melt downs?
Answer:
Melt downs are caused by too much heat in the power plant. During melt down the power plant makes more Radio active pollution.

Question 34.
How do power plants release power?
Answer:
Power plants produce power by using water, coal and gas.

Question 35.
How do Nuclear power plants produce power?
Answer:
By using Radio active elements like uranium.

Question 36.
How agriculture pollutes land and water?
Answer:
Use of fertilizers and pesticides in agriculture pollutes not only air but also land and water.

Question 37.
What is the result of deforestation?
Answer:
The destruction of forests and woods is called deforestation. It has resulted in the reduction of indigenous forests.

Question 38.
If forests reduce what would happen?
Answer:
If forests reduce the level of carbondioxide increases resulting to global warming.

Question 39.
In which devices chloro flouro carbons are used?
Answer:
Chloro flouro carbons (CFC) are used in refrigerators, Air Conditioners and aerosol sprays. CFC pollutes air by depleting the ozone layer.

Question 40.
How is mining cause pollution?
Answer:
Mining of coal and stone releases coal dust and stone dust that cause air pollution.

Question 41.
Why do the currently cars and buses not allowed to drive to the Taj Mahal?
Answer:
The motor vehicles and the Industries located in and around Agra for rubber processing, chemicals oil refinery of Mathura, iron foundries have been responsible for the colour change of Taj Mahal from white to yellow.

Question 42.
What did the Archeological department of lndia declared towards Taj Mahal?
Answer:
The Archeological department declared that 2\(\frac{1}{2}\) km around Taj Mahal is no drive zone.

Question 43.
What is the unforgettable tragedy of Bhopal?
Answer:
On second December 1984 about 3000 human beings died, about 5000 were paralized in just one night at Bhopal.

Question 44.
What is the reason for the tragedy at Bhopal?
Answer:
The reason for this is the leakage of Methyl isocynate into the air from an insecticide factory managed by union carbide.

Question 45.
What are the affects caused by air pollution?
Answer:
Air pollution causes certain diseases including shortness of breath, sore throat, chest pain, nausea, asthma, bronchitis and lung cancer.

Question 46.
How is like the air pollution?
Answer:
Air pollution is like a slow poison.

Question 47.
How to reduce air pollution from industries?
Answer:
Install electrostatic precipitators in the chimney of industries.

Question 48.
How to reduce pollution from vehicles?
Answer:
Reduce vehicular emission by using non-polluting fuels like CNG.

Question 49.
What is Vanamahotsav?
Answer:
We can protect plants and trees. On the day of Vanamahotsav lakhs of trees are planted in July every year.

Question 50.
Name one of the most polluted area in India.
Answer:
Patancheru, a suburban mandal in Medak district is a major industrial hub of the state is one of the most polluted area in India.

Question 51.
How are the villages badly affected by pollution?
Answer:
They are affected with some diseases like cancer, respiratory diseases and heart diseases by poisons in air, water and on land.

Question 52.
What is water pollution?
Answer:
The contamination of water with unwanted and harmful substances such as sewage, toxic chemicals, industrial waste etc., is called water pollution.

Question 53.
What is the character of normal water?
Answer:
Normal water is colourless without any smell or any unwanted substances. Water which is suitable for drinking is called potable water.

Question 54.
How Musi river got polluted?
Answer:
The people living near Musi throw large quantities of garbage, unwanted sewage, industrial waste, dead bodies, polythene bags, hot water and statues of deities and many other materials and made the river polluted.

Question 55.
What is definite source of pollution?
Answer:
Definite source of pollution is due to discharges from a single source, such as industrial site.

Question 56.
What is Biodegradable waste?
Answer:
Biodegradable waste consists of mainly human and animal waste.

Question 57.
How do plant nutrients pollute water?
Answer:
Phosphates sand nitrates – chemical fertilizers from agriculture run – off due to rain and industrial waste enter into water through sewage and pollute the water.

Question 58.
How is heat polluting water?
Answer:
As water, temperature increases, the amount of dissolved oxygen decreases. So thermal pollution often reduces the aquatic life diversity in water.

Question 59.
How is water polluted by sediment?
Answer:
Sediment pollution is formed by the sources such as constructional, agricultural, logging, flooding and city runoff.

Question 60.
What is Eutrophication?
Answer:
The enrichment of water by nutrients leading to excessive plant growth and duplication of oxygen is known as Eutrophication.

Question 61.
How is fluorine hazardous substance to ground water?
Answer:
Fluorine mixed in ground water cause dangerous disease called fluorosis.

Question 62.
What are 3R’s principles?
Answer:
The 3R’s principles are Reduce the usage of the materials, Reuse them for secondary purpose and Recycle the material again and again.

Question 63.
How should we maintain natural resources?
Answer:
We should keep the natural resources clean and healthy not only for us but also future generations.

8th Class Biology 10th Lesson Not For Drinking-Not For Breathing 2 Marks Important Questions and Answers

Question 1.
Complete this flow chart.

Answer:

1. Human activities
2. Volcanic eruptions
3. Forest fires
4. Sand cyclones
5. CFCs
6. Mining
7. Sewage
8. Industrial effluents
9. Toxic chemicals

Question 2.
Complete this flow chart.

Answer:
2) Industrial emissions
3) Atomic power plant radiation
4) Automobile exhausts
5) Fly ash

Question 3.
Heat can be a source of pollution ? How does it effect the aquatic life?
Answer:

1. As the water temperature increases, the amount of dissolved oxygen decreases.
2. Fish and plants require certain temperature and oxygen levels to survive.
3. So, thermal pollution often reduces the aquatic life diversity in the water.

8th Class Biology 10th Lesson Not For Drinking-Not For Breathing 4 Marks Important Questions and Answers

Question 1.
“It is much better to worship Ganesh Idol made of clay than Idol of Plaster of Paris” – said Kavitha. How do you support her ? How do you appreciate her attitude?
Answer:

1. I appreciate Kavitha’s attitude towards pollution free society.
2. ‘Plaster of Paris’ idol consists of different harmful chemicals. During “Nimajjanam” these are immersed in different water bodies which leads to water pollution.
3. Worshipping idols made with clay is eco-friendly.
4. Hence, I appreciate her environmental concern and eco-friendly nature.

Question 2.
Prepare some slogans which create awareness among people on air pollution.
Answer:

1. Stop pollution – Save life
2. Polluting water – Ending our lives
3. Save the nature – Nature will save you
4. Live and let live.
5. Nature is for humans need – Not for his greed.
6. Solar energy – Forever energy

Question 3.
What are the industries that cause water pollution?
Answer:

1. Textile industries
2. Chemical industries
3. Leather industries
4. Pesticide industries
5. Paint factories
6. Fertilizer industries – are causing water pollution.

8th Class Biology 10th Lesson Not For Drinking-Not For Breathing Important Questions and Answers

Question 1.
Natural resources are the divine gift for us by nature. We can use these resources in a meaningful way which helps us. If we destroy these resources human life will become an unsolvable puzzle. We should keep these resources clean and healthy not only for us but also for future generation.
Read the above paragraph and answer the questions given below.
a) How should we use our natural resources?
b) What would happen if we use natural resources injudiciously?
Answer:
a) We should use the natural resources discriminately. They are the gifts of nature. For example we should minimise the usage of fossil fuels and encourage the usage of alternative energy sources like solar energy and wind energy. We should use CNG in place of diesel and petrol in vehicles to restore fossil fuels for longer periods.
b) Man’s life on earth turns into a mysterious puzzle. Life is not possible for us.

Question 2.
Observe the above diagram and answer the following questions:

1. What does the diagram represent?
2. Which gas is more in quantity in the given picture?
3. What will happen if the percentage of carbon dioxide will increase in the atmosphere?
4. When can you say that carbon dioxide is not a pollutant?

Answer:

1. The above diagram tell us about the percentage of different gases present in our atmosphere.
2. Nitrogen.
3. The increase in CO₂ levels results in the increasing temperatures on the earth. As a result the glaciers in the polar region melt and rise in sea levels occur. It leads to submergence of many cities of the shore.
4. If CO₂ levels are below 0.03%, then it is considered as non – pollutant.

Question 3.
Read the following passage and answer the questions.
Here are two main sources of water pollution; definite sources and non-definite sources. Definite source pollution is due to discharges from a single source, such as an industrial site. It includes factories, waste water treatment facilities, septic systems, and other sources that are clearly discharging pollutants into water sources. Non definite-source pollution involves many small sources that combine to cause significant pollution. For instance, the movement of rain or irrigation water over land picks up pollutants such as fertilizers, herbicides and insecticides carries them into rivers, lakes, reservoirs, coastal waters, or groundwater. Non-definite sources are more difficult to identify, as they cannot be traced back to a particular location. Landfills can also be a non-definite source of pollution, if substances leach from the landfill into water supplies.
a) Which sources of water pollution are difficult to identify?
b) What are definite sources of water pollution? Give two examples.
Answer:
a) Non-definite
b) Definite source pollution is due to discharge from a single source such as an industrial site. Examples are factories, waste water treatment plants etc.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 7 Coal and Petroleum Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 7th Lesson Coal and Petroleum

8th Class Physical Science 7th Lesson Coal and Petroleum Textbook Questions and Answers

Improve Your Learning

Question 1.
Complete the given analogy.
i) Coal : ExhaustIble :: ———– : InexhaustIble
ii) Coaltar : ———– :: Coke : Manufacture of steel
iii) Petrochemicals : Plastic :: CNG : ———–
iv) Carbondioxide: Global warming :: ———– : Nausea
Answer:
i) Coal : ExhaustIble :: Solar energy : InexhaustIble
ii) Coaltar : Paints :: Coke : Manufacture of steel
iii) Petrochemicals : Plastic :: CNG : Fertilizer
iv) Carbondioxide: Global warming :: Heavy metals : Nausea

Question 2.
Match the following.
Group – A                                                Group – B
i) Natural resource                    ( )          a) Carbonisation
ii) Coal                                       ( )          b) Plastic chair
iii) Petrochemical product         ( )          c) Krishna and Godavari delta
iv) Natural gas                           ( )          d) Plankton
v) Petroleum                              ( )          e) Water
Answer:
i) e
ii) a
iii) b
iv) c
v) d

Question 3.
Multiple Choice Questions:
i) Which one of the following is less polluting fuel?
a) Natural Gas
b) Coal
c) Kerosene
d) Petrol
Answer:
ii) a

ii) The main constituent of coal is
a) Carbon
b) Oxygen
c) Air
d) Water
Answer:
iii) b

iii) Which one of the following material is used for making shoe polish?
a) Paraffin wax
b) Petrol
c) Diesel
d) Lubricating oil
Answer:
i) a

Question 4.
Fill in the blanks.
i) …………… was used in manufacture of steel. (Coke)
ii) The biproduct of coal used in synthetic dyes and paints is ………………. (coal tar)
iii) Coal was formed in areas where large amounts of ………………. was buried under the earth. (forests)
iv) ………………… gas which causes climate change and global warming. (Carbon dioxide)

Question 5.
Name the petroleum products is used for roads surfacing.
Answer:
A petroleum product of bitumen is used for roads surfacing in place of coal tar these days.

Question 6.
Explain the process of formation of petroleum in Earth. (OR)
Explain the process of formation of petroleum in the Earth.
Answer:
Petroleum was formed from the remains of tiny organisms called plankton that were found in the bottom of seas and oceans. Plankton have tiny droplets of oil inside their bodies.
As these organisms died, their bodies settled at the bottom of the sea or ocean and got covered with layers of sand and clay. Over millions of years, due to absence of air, high temperature and high pressure these dead organisms transformed into petroleum.

Question 7.
Project Work:
Compare a CNG run vehicle with that of a diesel run vehicle. What difference do you notice in both cases with respect to pollutants released, level of pollution and cost of fuel? Prepare a report on your findings. You can take the help of a driver to make a report on your observation.
Answer:

Name of the fuel	Cost of the fuel as on today	Pollutants liberated
Diesel/Petrol	Rs. 52.97/ Rs. 72.14 per litre	Carbon monoxide, carbon dioxide, hydro carbons, sulphur dioxide
CNG	Rs. 49 per kg	Carbon dioxide, sulphur dioxide, nitrous oxide

Question 8.
Project Work:
Choose five families of your neighbourhood, collect the information about the measures that they adopt to conserve energy resources in transport and cooking.
Make a report on your observation.
Answer:

The precautionary methods taken by them to conserve energy resources in transport and cooking.
In transport:

1. They do not using their motor vehicles for travelling smaller distances.
2. They are completing small distances by walk or by bicycle.
3. They are regularly servicing their vehicles.
4. They are regularly changing the engine oil of the vehicle.
5. They are travelling at prescribed speed and not applying brakes unnecessarily which increase the milage.

In cooking:

1. They are using cookers.
2. Not preparing to many fries which can increase the fuel consumption.
3. Regularly cleaning the burners of gas stove.
4. Cooking the food with sufficient water.

Question 9.
The following table shows the total power shortage percentage in India from 1991-1997. Show the data in the form of a bar graph taking shortage percentage for the years on the Y-axis and the years on the X-axis.

S.No.	Year	Shortage (%)
1	1991	7.9
2	1992	7.8
3	1993	8.3
4	1994	7.4
5	1995	7.1
6	1996	9.2
7	1997	11.5

a) Is the shortage percentage of power increasing or decreasing?
Answer:
The power shortage not followed a regular trend. It decreased from 1991 to 1992 and then increased in 1993 and then decreased upto 1995 and then increased upto 1997 from the table given.

b) If shortage percentage of power increases year by year, how will it affect on human life? Explain.
Answer:
The effect of shortage percentage of power on human life:
Agriculture: Agriculture mainly depends on electric power for water supply. If there is no sufficient power is available then the yield of food material decreases.
Industry: Industries mainly run with electric power. If electric power is not sufficient then it is major set back for their production.
Economy: Economy drastically affected by shortage of power which will also effects the economic status of people.
Health: Shortage of power also affects the health of people because many cured by operations which required power.
Science and Technology : The growth of science and technology completely get damage due to lack of power because they are mainly depend on power.
So shortage of power drastically affect human life.

Question 10.
Draw a flow chart showing exhaustible and inexhaustible resources and their use.
Answer:

Question 11.
Collect the information about place were we get coal, petroleum and natural gas in Andhra Pradesh and mark the places on outline map of Andhra Pradesh.
Answer:
Coal: Coal is not available in Andhra Pradesh.
Petroleum and Natural Gas: These reserves are spread over in Krishna and Godavari basins of our state.

Question 12.
How do you appreciate the efforts of human beings to discover an alternate energy source like coal and petroleum for their daily use?
Answer:
Earlier people used kiln using wood for cooking food and for travelling they used horses and bullock carts. There was no electricity so their life was miserable. The wood they were using produced lot of pollution. So they required a fuel not only for cooking but also travelling long distances.
In 19th century the use of coal as fuel was the major thing in development of human beings. Steam engine which used coal was invented during industrial revolution. Later electricity was produced from coal. During this period the steam engine was used to power everything from cloth looms to vehicles on land and water.
The petroleum was started as fuel in 1859 then it was used everywhere in the world because it was better fuel than coal and less pollutant. So people were using petroleum products for their needs that is for cooking, transport and machinery, etc. So discovery of using coal and petroleum as fuel changes the life of human beings. So we should have to appreciate human being for their discovery of an alternative energy source like coal and petroleum for their daily use.

Question 13.
Harshith said to his father, “Daddy we can save more fuel by using bicycle instead of bike for going to nearby places”. How do you appreciate Harshith’s comment?
Answer:
I would appreciate Harshith for his comment. We are wasting a lot of fuel for travelling near by places which can be covered either by bicycle or by walk. If we do like this a lot of fuel is consumed. Consuming fuel is producing fuel. So I thoroughly appreciate Harshith for his comment.

Question 14.
Why should people look for alternative sources of fossil fuel? (OR)
Write your opinion on the necessity of discovering an alternate energy sources to coal and petroleum.
Answer:
The entire research and development in the field of sourced energy shows that at present rate of use of the conventional energy sources like fossil fuels will not last for long and also burning fuels release carbon dioxide a green house gas, which causes a climate changes and leads to global warming.
Coal fired power plants emit mercury, selenium, arsenic, lead in addition to green house gases which are harmful to human health and environment and availability of coal decreasing rapidly.
So people should have to look for alternative sources of fossil fuels which are inexhaustible and pollution free.

Question 15.
Assume that you are a driver, what measures do you take to save petrol and diesel?
Answer:

1. I will thoroughly check whether the engine of the vehicle properly working or not otherwise the vehicle consume more fuel and also release poisonous gases.
2. I will thoroughly check the air in the tyres.
3. I did not unnecessarily apply brakes which will consume more fuel.
4. I will replace engine oils for every two or three months.
5. I will run the vehicle in prescribed speed which will increase the milage.
6. I did not allow overload in the vehicle.

Question 16.
“Crude oil and refined fuel when spills into the sea from tanker of ships by accident”. Discuss the consequences of this on environment.
Answer:
Crude oil and refined fuel spills into sea from tanker of ships by accident causes a damage to natural system and kill sea birds, mammals, shell fish and other organisms due to lack of dissolved oxygen in water as oil is less denser than water it floats on water and forming a layer called oil slink and oxygen does not enters into the water.

Question 17.
“The use of CNG and LPG as fuels for automobiles helps us to minimize air pollution and maintains ecological balance.” Do you agree with this statement? If yes explain.
Answer:
Yes, I will agree with the statement. CNG and LPG are completely combustible. CNG is less polluting and it is cleaner fuel releasing small quantity of harmful gases. Similarly LPG is also releases few polluting gases. CNG and LPG does not release hydrocarbons. They only release carbon dioxide and small quantities of sulphur dioxide and nitrous oxide. So using CNG and LPG as fuels for automobiles help us to minimize air pollution and maintains ecological balance.

8th Class Physical Science 7th Lesson Coal and Petroleum InText Questions and Answers

8th Class Physical Science Textbook Page No. 105

Question 1.
How is biodiversity affected by excessive use of fossil fuels?
Answer:
Biodiversity affected by excessive use of fossil fuels:

1. Burning fuels releases carbon dioxide a green house gas, which causes climate changes and leads to global warming.
2. Coal fired power plants emits mercury, selenium, arsenic, lead in addition to green house gases which is harmful to human health and environment.
3. Many paints made from petroleum and heavy metals release toxic products into air. These toxic products cause a variety of health problems including heart, lungs damage, nausea and dizziness.
   So these are harmful effects of excessive use of fossil fuels on biodiversity.

8th Class Physical Science 7th Lesson Coal and Petroleum Activities

Activity – 1

Question 1.
Identifying articles and materials used for various purposes.
Have a look at table. Column A gives the names of some activities and items. Ask your grandparents or other older people about the names of the materials then used for the items given in column A, and write them in column B. Then in column C, write the names of materials being used at present.
Answer:

From activity 1, you have a long list of materials. Some of them like wood, metals (Iron, Silver, Gold etc) were used ten years, fifty years even hundred years ago. Do your grand parents remember using plastic when they were young?
Now think and wirte the answers:
a) How many of these materials were available 10 years ago?
Answer:
Plastic, iron, gold and silver articles were available 10 years ago.

b) How many of these materials were available 50 years ago?
Answer:
The articles made up of wood, iron, silver, gold are available 50 years ago and also articles made up of clay. There is no plastic articles.

c) How many of these materials were available 100 years ago?
Answer:
The articles made up of clay, wood, iron, silver, gold were available 100 years ago.

Activity – 2

Question 2.
List out the natural resources which are limited and which are abundant arid record in table.
Answer:

Resources abundant	Solar energy, wind energy, tidal energy, biomass enery, water
Resources limited	Coal, petroleum, natural gas

a) What will happen if fossil fuel like coal and petroleum are completely exhausted?
Answer:

1. There would be no fuel for cooking.
2. There would be no fuel for transport.
3. There would be no fuel for running machinery.
4. There would be no fuel for producing electricity.
   So life on earth become miserable.

b) What would be our future energy resources?
Answer:
The future energy resources are hydro electric power, solar energy, wind energy, tidal energy, geothermal energy, Ocean Thermal Energy Conversion (OTEC), biomass energy.

c) Are the fossil fuel resources available plenty to meet the future energy needs?
Answer:
No, a survey gives an information that about 2015 the world people would consume half of total reserves of petroleum. Coal also exhaustible resource. We can meet our needs with coal for another 250 – 300 years at the current rate of use.

d) What actions required to meet the future energy needs?
Answer:

1. Do not waste fuel for unnecessary activities.
2. The energy should be properly utilized and the wastage should be minimized.
3. Usage of bicycle in place of motor vehicles for small distances.
4. Using road transport vehicles for travelling larger distances which will minimize fuel consumption.
5. The engine of a vehicle thoroughly serviced in order to minimize fuel consumption.
6. Alternative sources like solar energy, wind energy, tidal energy more utilized.

Activity – 3

Question 3.
Identifying various uses of petroleum.
Look at the figure and find the other uses of petroleum and its products. Fill in the table.

Answer:

Activity – 4

Question 4.
Identifying uses of coal products:

Observe the above picture and list out the uses of coal products in the following table. You can collect more information by the discussion with elders and with your friends.
Answer:

Lab Activity

Conduct an experiment to show that when we heat high quality coal, a gas evolves which can be burnt. (OR)
What are the materials required to demonstrate “burning of coal”? Draw the diagram of the experimental setup. (OR)
How do you prove a high quality coal on heating produces a burning gas?
Answer:
Aim: To show that when we heat high quality of coal a gas evolves which can burn. Material required : Two boiling tubes, rubber corks, iron stands, delivery tube, jet tube, bunsen burner.
Procedure: Take a spoon of powdered coal into a hard boiling tube and fix it to a stand as shown in figure. Close the test tube with a rubber cork and connect it to another.
boiling tube which is partially filled with water and has fixed to other stand, with the help of ‘U’ shaped delivery tube. Arrange a jet tube to the cork of second boiling tube. Heat the boiling tube containing coal strongly with the help of bunsen burner.

We may notice that brownish black vapours evolved in the first boiling tube. These vapours are passed through water in the second boiling tube. Colourless gas bubbles evolve from the water. If we burn the gas that is evolving through the jet tube we can witness a bright flame at the nozzle. This shows when we heat high quality coal a gas evolves which can burn.

Activity – 5

Question 5.
Group discussion on misuse of fuel resources and its consequences.
Discuss in small groups how fuel resources are being misused in our daily life while doing various activities like
a) transportation, b) cooking and c) industrial use.
Answer:
Misuse of fuel in transportation:

1. Do not stopping the engine at traffic signals.
2. Running the vehicle with more speed than prescribed speed.
3. Unnecessarily using brakes.
4. Not servicing the engine regularly.
5. Not changing the engine oil regularly.
6. Not filling air in the tyres regularly.
7. Carrying overload in the vehicle.
8. Using vehicles for smaller distances.

Misuse of fuel in cooking:

1. Not stopping the burners when the cooking is over.
2. Using more water than required which will consume more fuel.
3. Not checking the burners regularly whether they are any dust particles which will lead more consumption of fuel.
4. Preparing more fries which required more fuel.

Misuse of fuel in industries:

1. Machinery is not properly working.
2. Any flaws in the machinery.
3. Not doing regularly maintenance of machinery.
4. Lubricants are not used properly.

a) What are the consequences of misuse of fuels?
Answer:

1. Fossil fuels like coal and petroleum are completely exhausted.
2. Misuse also leads to environmental pollution due to release of harmful gases like carbon monoxide.

b) What methods could you suggest to prevent the misuse of fuels?
Answer:
In transportation:

1. Drive at a constant and moderate speed as far as possible.
2. Switch off the engine at traffic lights or at a place where you have to wait.
3. Ensure correct tyre pressure.
4. Ensure regular maintenance of the vehicle.

In cooking:

1. Stop the burners when the cooking is over.
2. Use sufficient water for cooking.
3. Do not prepare more frying food.
4. Ensure regular maintenance of the gas stove.

In industry:

1. Correct the flaws in the machinery.
2. Ensure regular maintenance of machinery.
3. Lubricants are used whenever necessary.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 1 Force Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 1st Lesson Force

8th Class Physical Science 1st Lesson Force Textbook Questions and Answers

Improve Your Learning

Question 1.
What is a force? What changes can be produced by a force?
Answer:
Force: A push or a pull of an object is called a force.
Changes produced by a force:

1. A force can change the state of motion of an object.
2. A force can change the shape of an object.

Question 2.
State an example for a situation mentioned below in which a force:
a) Changes the speed of an object.
b) Changes the shape of an object.
c) Changes the direction of an object.
Answer:
a) Force changes the speed of an object:
A ball at rest begins to move when a force is applied on it that shows force changes the speed of an object.
b) Force changes the shape of an object:
Take a plastic or metal scale placed between two bricks and put some weight at the centre of the scale. We observe that force changes its shape.
c) Force changes the direction of an object:
Kick a moving football with some angle then we can observe the change in the direction of football.

Question 3.
How can you differentiate between a contact force and a force at a distance?
(OR)
Distinguish between a contact force and a force at a distance.
Answer:

Contact force	A force at a distance
1. Force which results when there is a direct physical contact between two interacting objects is known as contact force.	1. The force which occurs without any physical contact between two objects is known as a force at a distance or field force.
2. The two objects have direct contact.	2. No contact.
3. For example, the tyres of a bicycle has direct contact with the surface of the road.	3. For example, the attraction of two magnets.

Question 4.
Give two examples each for a contact force and a force at a distance.
Answer:
Contact force:
e.g.: 1) Muscular force 2) Frictional force Force at a distance:
e.g.: 1) Magnetic force 2) Electrostatic force

Question 5.
Detect the errors in the following statement and rewrite it making necessary corrections.
“Because the car is at rest, no forces are acting on it.”
Answer:
The object is said to be at rest when no forces are acting on it or net force acting on it is zero. So the statement should be corrected like this “Because the car is at rest, no forces are acting on it or net force on the car is zero.”

Question 6.
Why do tools meant for cutting always have sharp edges?
Answer:
The tools meant for cutting have sharp edges because of smaller contact area they exerts more pressure on objects and cutting of objects are easy.

Question 7.
Objects change their state of motion due to the net force acting on them. Do you agree with this statement ? Discuss with examples.
Answer:
Yes, we can agree with this statement. Net force can increase or decrease the speed of an object. Force can also change the direction of an object.
Hence we conclude that net force can change the state of motion of an object.
Some examples:

1. If we kick the ball it will move from state of rest.
2. If we stop the running ball it will come to state of rest.
3. If we through a ball on the ground it will come to rest after sometime due to gravitational force acting on it.
4. If we pull the chair, it will move due to muscular force acting on it.

Question 8.
When you push a heavy object, it doesn’t move. Explain the reason in terms of net force.
Answer:

When we apply force on a heavy object it has to overcome frictional force in order to move. If the force applied is less than the frictional force then the net force (f – F) is insufficient to move the object.

Question 9.
Find net forces from the following diagrams:

Answer:
a) Net force is 6N along horizontal direction towards right.
b) Net force is zero.
c) Net force is 14N along horizontal direction towards right.
d) Net force is 1 N upwards in vertical direction.

Question 10.
Imagine that friction has disappeared from the earth. What will happen? Explain.
Answer:
If friction has disappeared from the earth then

1. we cannot walk or run.
2. we will not have any cars or bicycles because all of them move due to friction.
3. no building could be constructed.
4. carpenters will not able to smoothen surfaces.
5. we could not fix nail on the wall.
6. it will not possible to write with pen or pencil.
7. we will not able to hold any appliances such as hammer, soap, etc.

Question 11.
Karthik is observing the live telecast of a one day cricket match. He noticed motion of a roller on the pitch during lunch break. He thought about various forces acting on the roller and the net force when it is in motion. Many questions arose in his mind regarding the direction of the net force. Can you guess what would be those questions?
Answer:

1. Why there is no motion for roller in vertical direction?
2. What are the forces acting in the vertical direction?
3. What are the forces acting in the horizontal direction?
4. Why there is motion in the horizontal direction for roller?

Question 12.
a) Take two identical straws and suspend one of them freely. Rub the other straw with a piece of paper. Bring the rubbed end of the straw near the suspended one. What do you observe from this activity? Can you tell which type of force is it?
b) Comb your dry hair. Bring the comb near small pieces of paper. What do you observe? Explain.
Answer:
a) The rubbed end of the straw attracts the suspend straw when it is brought near to it. The reason is that when the straw is rubbed with a paper, it acquires an electrostatic charge on its surface and the suspended straw near it acquires opposite charge.
b) When we comb dry hair and bring small pieces of paper they are attracted by comb the reason is when we comb dry hair, it acquires electrostatic charge and paper pieces brought near to it acquire opposite charge there by they are attracted by comb.

Question 13.
Collect pictures from various sources like internet, magazines, newspapers, etc. to illustrate contact forces, forces and prepare a scrap book.
Answer:

Question 14.
A stick is placed on steps as shown in the figure. Draw normal forces on the stick.

Answer:

Question 15.
A monkey hangs stationary at the end of the vertical vine. What forces act on the monkey
Answer:
a) The weight of the monkey downward direction.
b) The normal force by branch upward direction.
c) The frictional force exerted by branch along the horizontal direction.

Question 16.
If you push on a heavy box which is at rest, you must exert some force to start its motion. However, once the box is sliding, you can apply a lesser force to maintain that motion. Why?
Answer:
When the box is sliding, the contact points on its surface do not get enough time to lock in to the contact points on the floor. So friction is less when compared with box at rest so we required to apply lesser force to maintain motion.

Question 17.
How do you increase the pressure by keeping
(a) area unchanged and (b) force unchanged?
Answer:
Pressure P = hdg. So pressure can be depend on height of air column, density of air and acceleration due to gravity.
So pressure can be increased by increasing length of air column at a particular place and for a particular gas.

Question 18.
Design and conduct experiments to test few ways how friction may be reduced.
Answer:
Friction is due to the roughness of surfaces. It can be reduced by the following methods.
– By polishing the rough surface.
– By applying lubricants like oil and grease to the surfaces.
– By spreading powder on the rough surface like carromboard.
– By using soap and detergent solutions, etc.
Experiment: The rusted pulley makes a rattling noise. Apply some oil in between the wheel and axle. The sound is reduced and now it works smoothly.

Question 19.
Observe the figure and find in which direction the force of friction acts. Also indicate the normal forces and their directions.

Answer:

f: force of friction
N₁, N₂, N₃, N₄ are normal forces.

Question 20.
A man is standing still on a level floor. What forces act on him? Draw a free body diagram (FBD) to show all forces acting on him.
Answer:
The forces acting on the man:

Along vertical direction:

1. Weight of the man or gravitational force acting vertically downwards.
2. Normal force or reaction applied by the floor vertically up.

Along horizontal direction:
Frictional force applied by the floor on the man.

Question 21.
How do you appreciate the role of friction in facilitating our various activities?
Answer:
Every motion that occurs on earth depends upon friction. For example, we are unable to walk if there is no friction and we cannot write with a pen and we cannot construct a building and there should be no vehicles without friction.
So without friction there is no motion on earth. So friction is required for better living of human beings.

8th Class Physical Science 1st Lesson Force InText Questions and Answers

8th Class Physical Science Textbook Page No. 3

Question 1.
When an object slips off your hand, it always falls down. What pulls it down?
Answer:
Gravitational force.

Question 2.
If you roll a ball on a level ground, it slows down and after sometime it will come to a stop. What makes the ball stop?
Answer:
Frictional force acting between floor and ball.

Question 3.
What forces acting on objects, change their state or state of motion?
Answer:
Contact force and force at a distance.

Question 4.
Why does the needle of a magnetic compass move when we place a bar magnet near to it?
Answer:
A force at a distance or field force acts on the needle. So, the needle of a magnetic compass moves when we place a bar magnet near it.

Question 5.
Why does the toothpaste come out when we press the tube?
Answer:
A contact force acts between our hand and tube. So, the toothpaste comes out when we press it.

Question 6.
Have you observe the difference between the force applied by a magnet on the needle of a compass and the force you applied on the tube?
Answer:
First one is force at a distance and the second one is contact force.

8th Class Physical Science Textbook Page No. 4

Question 7.
If a pen slips off from our hands it falls down to the floor.
a) Why does the pen fall down ?
b) What is the force which pulls the pen down ?
Answer:
a) Due to increase of gravitational pull of the earth than the normal force,
b) Gravitational pull of the earth.

Question 8.
If we keep the pen on a table, it does not fall down. Why ?
Answer:
As the normal force and gravitational pull of the earth are equal, it does not fall down.

Question 9.
a) Why does a stone thrown up into the sky fall back to the earth?
b) Why do rivers flow down to the sea?
c) How does the earth hold the atmosphere?
d) Is there any force pulling the objects towards earth?
Answer:
For all the above questions, the answer is ‘due to gravitational pull of the earth on the nearer bodies of the earth’.

8th Class Physical Science Textbook Page No. 6

Question 10.
In all the actions that we perform in our daily life like brushing, bathing, eating, writing, driving and walking ; we have to exert a force. Do you know from where the force comes?
Answer:
The force comes from our muscles.

8th Class Physical Science Textbook Page No. 8

Question 11.
Did you ever experience slipping on a floor? What conditions caused you to slip?
Answer:
Yes, it was due to less friction between my foot and floor.

Question 12.
Did you experience slipping while you are walking on wet mud ? Why do most of road accidents happen during rainy days?
Answer:
Yes, in the wet mud the friction is very less and wet mud acts as a lubricant between our feet and floor. During rainy season the mud or road will be wet and as mentioned above the friction will be less, so most accidents happen.

Question 13.
Would it be possible to drive a car if there were no friction between the tyres and the road?
Answer:
No, we can’t stop the car as there is no friction in case of no friction between the tyres of car and the road. We can drive, but the car would not get any control.

Question 14.
Place your science book on the table. Is it in a state of rest?
Answer:
Yes.

8th Class Physical Science Textbook Page No. 9

Question 15.
What is the state of the stone?
Answer:
At rest.

Question 16.
What forces are acting on it?
Answer:
Tension and gravitational pull of the earth.

Question 17.
What will happen if the thread is broken?
Answer:
The gravitational pull of the earth increases and the stone falls down.

Question 18.
What do we call this force ? (the force supporting the stone)
Answer:
Tension.

8th Class Physical Science Textbook Page No. 13

Question 19.
You might have seen children playing with a rubber tyre by pushing it with a stick.
They push the tyre again and again with the stick to increase its speed,
a) Do you understand why the speed of the tyre increases whenever it is pushed by the stick?
Answer:
With every push they are applying a little more force on the moving tyre in the direction of motion. Hence the speed of the tyre increases continuously.
b) Give some more examples where the object speeds up or slows down or a change may occur in its direction of motion, when we exert a force on it?
Answer:
If wind blows in the direction of motion of bicycle the speed of bicycle increases. If wind blows in the opposite direction of motion of bicycle the speed of bicycle decreases.

Think and Discuss

8th Class Physical Science Textbook Page No. 5

Question 1.
A cricket ball of mass’m’ is thrown upward with some initial speed. If the air resistance is neglected, what forces are acting on the ball when it reaches (a) half its maximum height and (b) its maximum height?
Answer:
The forces which are acting on the ball thrown vertically upward:
a) At half of its maximum height:

1. The remaining force which acts vertically upwards (some force that we applied is utilized in reaching half of maximum height).
2. The gravitational force downwards.

b) At maximum height:
Gravitational force acts downward direction (The applied force is completely utilized in reaching maximum height).

8th Class Physical Science Textbook Page No. 6

Question 2.
Two identical bars, one which is steel and the other a magnet, are painted with the same colour. How can you tell which one is the magnet using only these two bars? (don’t break the bars)
Answer:
The bar which attracts the other bar is magnet. The other bar is magnetic material that is steel.

8th Class Physical Science Textbook Page No. 8

Question 3.
A book placed on a table is at rest. Is the force of friction acting on it or not ? Explain.
Answer:
Friction is caused by the irregularities on the two surfaces in contact. Even those surfaces which appear very smooth have large number of minute irregularities on them. Irregularities on the two surfaces lock into one another. So a book placed on a table is at rest experiences frictional force.

8th Class Physical Science Textbook Page No. 10

Question 4.
A system of two bodies A and B are placed as shown in figure. How many forces are acting on A and B respectively?
Answer:

On A

1. Normal force exerts by floor vertically upwards.
2. Weight of A vertically downwards.
3. Frictional force exerts floor along horizontal direction.

On B

1. Normal force exerted by surface of A vertically upwards.
2. Weight of B vertically downwards.
3. Frictional force exerts by surface of A along horizontal direction.

Question 5.
Why is it necessary to separate contact force into a normal force and frictional force? Give at least two reasons.
Answer:
Reasons:

1. In order to know what are the forces acting on the object.
2. To know the net force acting on the body.
3. To know the direction of motion of an object.

8th Class Physical Science Textbook Page No. 12

Question 6.
Play arm wrestling with your Mend. How can you explain the winning of the game by using the concept of net force?
Answer:
The person we exerts more muscular force tends to win.

Question 7.
Name the forces acting on arm and their direction while playing the game. Try to draw FBD for this situation.
Answer:
The muscular force, normal force and weight (gravitational force).

8th Class Physical Science Textbook Page No. 15

Question 8.
Does pressure have direction? Explain.
Answer:
Pressure exerts in all directions. So there is no specified direction for pressure. So we does not consider pressure has direction i.e., it has only magnitude but not direction. So it is a scalar quantity.

8th Class Physical Science 1st Lesson Force Activities

Activity – 1

Question 1.
Identifying push or puli:
Write push or pull in the blank boxes given below. If you feel that the action involves both push and pull, write both in the boxes.
Answer:

a) List three more activities where we exert force which appears as a push.
Answer:

1. Pushing a repaired car.
2. A football player taking a penalty kick.
3. A cricket ball hit by a batsman.

b) List three more activities where we exert a force as a pull.
Answer:

1. Drawing bucket of water from a well.
2. Opening a drawer.
3. In a game of tug of war, two teams pull the rope in the opposite directions.

c) State three actions which involve both push and pull.
Answer:

1. Moving a book front or back on a table.
2. Opening or shutting a door.
3. Cleaning the floor with a cloth.

d) Shall we call the effort done on an object by means of pushing or pulling as a force exerted on the object?
Answer:
Yes, it is called force.

e) When an object slips off your hand, it always falls down. What pulls it down?
Answer:
Gravitational force.

f) If you roll a ball on a level ground, it slows down and after sometime it will come to a stop. What makes the bail stop?
Answer:
Frictional force acting between floor and ball.

g) What forces acting on objects, change their state or state of motion?
Answer:
Contact force and force at a distance.
Types of forces:

h) Why does the needle of a magnetic compass move when we place a bar magnet near it?
Answer:
Due to magnetic force of magnet.

i) Why does the toothpaste come out when we press the tube?
Answer:
Due to muscular force applied by us on toothpaste.

j) Have you observe the difference between the force applied by a magnet on the needle of a compass and the force you applied on the tube?
Answer:
First one is force at a distance and the second one is contact force.

Activity – 2

Question 2.
Observing the magnetic force :
Take a sewing needle. Rub it with a bar magnet several times always moving the magnet in the same direction.
a) Does the needle get magnetised?
Answer:
Yes. Identify south and north pole of the magnetised needle. Pin a red coloured foam ball to South pole and white ball to North pole of the needle, then drop it in a bowl of water it floats.
Make another needle in the same way. Float both the needles side by side such that like ends facing each other.

b) What happens to the needles? How do they move?
Answer:
They repel each other. They move backwards to each other.

c) Now place the needles in such a way that unlike ends face each other. How do they push or pull each other?
Answer:
They pull each other that means they are attracted.

d) What is this pull or push between two poles called?
Answer:
Magnetic force.

Activity – 3

Question 3.
Observing electrostatic forces :
Take a balloon. Inflate it and tie up the open end. Now cut a paper into small pieces and place them on floor. Rub the balloon with a paper and using the balloon near the pieces of the paper.
a) Are the bits of paper pulled towards the balloon?
Answer:
Yes, the bits of papers pulled towards balloon.

b) Why does the balloon pull or attracts the pieces of paper?
Answer:
When the balloon is rubbed with a paper it acquires charge and it induces opposite charge which brought near to it. So the pieces of paper are attracted by balloon.

c) Try to use pepper and salt in the place of pieces of paper. What do you observe?
Answer:
They do not attracted by the balloon.
Gravitational force: It is our common experience that if a pen slips off from our hands it falls down to the floor.

d) Why does the pen fall down?
Answer:
Some force is acting in downward direction.

e) What is the force which pulls the pen down?
Answer:
Gravitational force exerted by the earth.

f) If we keep the same pen on a table, it does not fall down. Why?
Answer:
The gravitational force exerted by earth is balanced by normal force between pen and surface of the table.

g) Why does a stone thrown up into the sky fall back to the earth?
Answer:
Due to gravitational pull.

h) Why do the rivers flow down to the sea?
Answer:
Due to gravitational force exerted by earth.

i) How does the earth hold the atmosphere?
Answer:
Due to gravitational force exerted by earth.

j) Is there any force pulling the objects towards earth?
Answer:
The force exerted by earth is gravitational force.

k) Where does gravitational force exists?
Answer:
The gravitational force exists everywhere in the universe between the objects having masses.

Activity – 4

Question 4.
Visualizing magnetic field:

Take a bar magnet and place it on a table. Place a thick white paper over it.
On the paper, sprinkle fine powder of iron as shown in the figure. Tab the table or the paper gently with pen/pencil.
a) Do you find the pattern of iron filings there?
Answer:
Yes.

b) Rotate the magnet in different directions and do the same. How has the pattern changed?
Answer:
In different directions that we will observe different patterns.

c) Why the iron filings set pattern around magnet?
Answer:
Iron filings set themselves in a pattern because of magnetic field created by the magnet.

d) What is the space around the magnet called?
Answer:
The space around magnet where its influence can be detected is called magnetic field.

Activity – 5

Question 5.
Preparing a list of examples for muscular force:
List at least ten activities where we apply muscular force to perform various tasks in table.
Answer:

List of activities where we exert force

Lowering a basket

Lifting a bucket from a well

Pushing a car

Pulling a cow

Opening a drawer

Opening or shutting a door

Hitting a cricket ball with a bat

Playing badminton

Digging a bore well

Raising a flag

Activity – 6

Question 6.
Observing the changes in any muscle while working:
Do you feel your muscle get tightened while performing a physical activity? What could be the reason for it?
Answer:
Take a dumbbell and lift it in different ways and observe while doing this exercise which muscle is going to be shortened.
The term muscles refer to multiple bundles of muscle cells held together. Muscles are normally arranged in such a way that, as one group of muscles contract or shortens, another group relaxes or expands. So we feel the muscles get tightened while performing any physical activity.
Force of friction:
When you roll a ball on a level ground it invariably stops after sometime.
a) Why does the ball stop?
Answer:
Due to some opposing force.

b) Is there any hidden force which brings it to stop?
Answer:
Frictional force between floor and ball.

c) If you stop peddling your bicycle on a level road you observe that its speed decreases gradually. Why does the speed of bicycle decrease gradually? Is there any force acting on it which tends to reduce its speed?
Answer:
The speed of bicycle decreases gradually due to some opposing force. The force is frictional force between road and tyre.

Activity – 7

Question 7.
Observing the motion of a ball on different surfaces.
Try to roll a ball on different surfaces like carpet, rough roads, smooth floor, etc. On which surface does the ball roll farther ?
Answer:
On the smooth floor it roll farther the reason is the force of resistance to the motion seems to be more on the rough surfaces than on the smooth surfaces.

Activity – 8

Question 8.
Observing the motion of objects on an inclined plane:
Take a tray. Place a small ice cube, eraser and a rupee coin to stay on a line at one end of the tray. Now slowly lift this end of the tray as shown below.

a) What do you observe?
Answer:
The three objects tends to slide downwards.

b) Which of these three objects slides down first? Why?
Answer:
Ice cube rolls first because the melting of ice takes place
and water acts as lubricant and decrease the frictional force.

c) Do all objects experience the same resistance to motion? If not why?
Answer:
No, all of them does not experience same resistance in motion because the irregularities present in the surfaces of the objects are different.

d) Which of the objects experiences more resistance to motion? Why?
Answer:
The eraser experiences more frictional force due to more normal force exerted on the surface of eraser.

e) Why the change in resistance experienced by the objects though they all slide down on the same plane?
Answer:
The frictional force depends on nature of surface. So different surfaces exerts differed frictional forces, therefore there is a change in resistance.

f) Did you ever experience slipping on a floor?
Answer:
Yes.

g) What conditions caused you to slip?
Answer:
When we walk on a smooth floor.

h) Did you experience slipping while you are walking on wet mud?
Answer:
Yes.

i) Why do most road accidents happen during rainy days?
Answer:
Rain water acts as lubricant which decrease the frictional force between tyre and road thereby vehicles slip more due to that accidents occur more on rainy days.

j) Would it be possible to drive a car if there were no friction between the tyres of car and the road?
Answer:
No, it is not possible.
Normal force:

k) Place your science book on the table. Is it in a state of rest?
Answer:
Yes.

l) Is there any force acting on that book?
Answer:
Yes.

m) Imagine that the table has disappeared suddenly by magic. What will happen then?
Answer:
The book will fall down due to gravitational pull of the earth.

n) When a book is lying on the table, the gravity pulls the book down all the time but it does not fall down. Why?
Answer:
It is supported by the table.

o) What is the force which supports against gravity by pushing it upward called?
Answer:
The force that a solid force exerts on any object in the normal direction is called the normal force.
Tension:
As shown in the figure a stone is suspended with the help of a thread and its free end is tied to the ceiling.

p) What is the state of the stone?
Answer:
The stone is at the state of rest.

q) What are the forces acting on it?
Answer:
Gravitational force acts downwards and the force exerted by string acts upwards.

r) What will happen if the thread is broken?
Answer:
The stone will fall downwards due to gravitational pull.

s) For a stone tied to the thread there exists a force which supports the stone against gavity by pulling upwards. What do we call this force?
Answer:

It is called tension.

t) What is tension?
Answer:
When we stretch a rope or a thread the tightness of rope or thread is called tension. Tension is a contact force.

Lab Activity

Write an activity to measure limiting force beared by a thread:
(OR)
Conduct an experiment to find the limiting force that can be borne by different threads.
Answer:
Aim: To find the limiting force that can be borne by a thread.
Material used: Spring balance, weights, light threads, weight hanger.
Procedure:
i) Arrange the system as shown in figure. Put some small weights like 50 gm on the weight hanger and note the readings of the spring balance. Now, add some more weights to the hanger and note the readings of spring balance. Do the same till the thread is broken.

ii) Separate the whole system from the ceiling, and tie the thread to weight hanger and now slowly pull up the whole system with your hand when there is a small weight on the hanger.
Note down the readings of the balance when the thread is broken that give limiting force beared by a thread.

a) What do you observe from the readings when it pulled up and released to move down?
Answer:
We will observe from the readings that another force is worked on this system when it is pulled up and released move down.

b) Is the thread broken when the whole system is pulled quickly up?
Answer:
No, the thread is not broken when the whole system is pulled quickly up.

Net force:
a) What are the forces acting on an object placed on a floor?
Answer:
Gravitational force (vertically down) and normal force (vertically up).

b) Do you observe any change in the state of rest of that object, because of these forces and why?
Answer:
No, because these forces acting on the object are equal and opposite in direction. Hence there is no change in its state.

c) What is the net force acting on object in this case?
Answer:
Zero.
Imagine that the same object is kept in a lift which is accelerating.

d) How many forces are acting on this object?
Answer:
Weight of the object (vertically down) and accelerating force (vertically up).

e) Is the net force acting on the object zero? Why?
Answer:
No, it is not equal to zero because the object is moving upward with non-uniform motion.

Activity – 9

Question 9.
Effects of net force acting on a table :
a) Try to push a heavy wooden table. Is it hard to push ?
Answer:
Yes.

b) Ask your Mend to help in pushing the table in the same direction, as shown in the figure. Do you find it easier to move the table now? Why?

Answer:
Yes, because both of us applying force in the same direction on the table. So resultant applied force increases so it is easier to move the table.

c) Now ask your Mend to push the table from the opposite side as shown in the figure.

Does it move ? If it moves, then in which direction does it move?
Answer:
If both of us apply same force with equal magnitude the table does not move.
If it moves, it moves in the direction where there is larger force is applied.

d) If we apply two unequal forces F₁, F₂ applied in the same direction and opposite direction (F₁ > F₂) then what is the net force ?

Answer:

If F₁, F₂ act in same direction, net force = F₁ + F₂
If F₁, F₂ act in opposite direction, net force = F₁ + (-F₂) = F₁ – F₂

Activity – 10

Question 10.
Effects of stretched rubber bands on fingers:
Take a rubber band, stretch it using your fingers. When you stretch the rubber band it exerts force on your fingers and you feel the force of pull on your fingers.
a) What happens if you add one more similar rubber band around your fingers and stretch both together to the same length ? Do you feel the combination of two bands exerts a larger force than that of one?
Answer:
Yes, the net force is the combination of two forces. So they exerts larger force.

b) Let us say the force exerted by one rubber band is F units and the force exerted by the second rubber band is also F units. Then what will be the net force of two rubber bands?
Answer:
Net force (F_net) = F + F
= 2F units

c) What is the net force acting on your finger when three, four, etc. rubber bands are used?
Answer:
If three rubber bands are used the net force = F + F + F = 3F
If four rubber bands are used the net force = F + F + F + F = 4F

How to calculate net force from free body diagrams:
Let a car moving with non-uniform speed along a road.
What are the forces acting on the car? What is the net force acting along the vertical direction? What is the net force acting along horizontal direction? Draw all the relevant forces acting on the body by using free body diagram.
Choose a coordinate system with X and Y axis in figure. Sign convention is to be taken along X and Y directions. Add forces algebraically with sign conventions along X and Y axis respectively.
Answer:

The forces acting on the car are, shown in FBD (Free body diagram).
They are Force applied by the engine = F
Friction applied by road = f
Normal forces are N₁ and N₂.
Gravitational force (F_g) = W
∴ Net force along X – direction,
F_{net, x} = f – F
(∵ They act in opposite direction)
Net force along Y – direction,
F_{net, y} = (N₁ + N₂) – W
(∵ They act in opposite direction)

Activity – 11

Question 11.
Effect of force on the direction of motion and state of the body:
Place a football on the ground. The ball will remain in the state of rest unless someone kicks the ball.

a) Kick the ball what happens? Does the ball start moving?
Answer:
Yes, the ball start moving

b) Kick the moving ball again in the same direction.
What will be the result?
Answer:
The speed of the ball increases.

c) Place your hand or leg against the ball. Does the ball stop ?
Answer:
Yes. You might have seen children playing with a rubber tyre by pushing it with a stick. They push the tyre again and again with the stick to increase its speed.

d) Do you understand why the speed of the tyre increases whenever it is pushed by the stick?
Answer:
With every push they are applying a little more force on the moving tyre in the direction of motion. Hence speed of the tyre increases continuously.

e) What happens if net force acts opposite to the motion of an object ?
Answer:
The net force acts opposite to the direction of motion of an object then it either slows down the object or brings it to a stop.

f) Give some more examples where the object speeds up or slows down or a change may occur in its direction of motion, when we exert a force on it?
Answer:
If wind blows in the direction of motion of bicycle, the speed of bicycle increases. If wind blows in the opposite direction of motion of bicycle, the speed of bicycle decreases.

Activity – 12

Question 12.
Effects of net force on direction of moving object:

a) Hit a carrom coin with the striker. Ask your friends to do the same. Does the coin move in the same direction in each case ?
If not why?
Answer:
No, you can observe that when you hit the coin with the striker not only does the coin changes its direction, but the striker changes its direction too.

b) What might be the cause of that?
Answer:
The net force makes a stationary object move and also changes the speed and direction of moving object.

c) Does the force change only the state of motion ? Are there any other effects of force?
Answer:
No, the force changes the direction.

Activity – 13

Question 13.
Effects of force on the shape of an object:
In the given table some situations are given in the first column showing how the force is applied on an object. Observe the shape of the objects carefully before and after applying the force. Mark T for temporary change and ‘P’ for permanent change.
Answer:

Action of force	Change in shape (temporary / permanent)
Stretching rubber band	Temporary
Squeezing sponge	Temporary
Tearing paper	Permanent
Crushing plastic bottle	Permanent
Making chapathi	Permanent
Breaking glass	Permanent

Activity – 14

Question 14.
Change in effect of force with area of contact:
a) Take a pencil. Just push its rounded end on your palm. Now push from the other side of the pencil gently so that the sharp end is on your palm. What difference did you experience? Why?
Answer:
It applies more force when sharp end touches the palm.

b) Why do the porters place turbans (talapaga) on their head when they have to carry heavy loads?
Answer:
The reason is, they are increasing surface area there by they are decreasing the force applied by object.

c) Why do school bags and shopping bags have broad straps as handles?
Answer:
As the surface area increases the force applied by object decreases.

d) Have you ever wondered why the lorries carrying loads have a large number of broader tyres?
Answer:
The effect of force depends on the area of contact on which the force is acting. When the area of contact is more then the force acting is less. So lorries have a large number of broader tyres to carry heavy loads.

Activity – 15

Question 15.
Identifying effects of force:
Take two trays. Fill both the trays with lime powder or fine sand. Now take two rectangular bricks of equal mass and similar shape. Keep one brick vertically in one tray and the other brick horizontally in the second tray.
a) Do both bricks sink to the same depth in lime powder? If not why?
Answer:
No, both does not sink to the same depth. The brick standing vertically sink deeper in lime powder than the brick standing horizontally The reason is the contact area or surface area on which force is acting is smaller and hence pressure exerted by the brick is more.

b) Why does the sharper side of a knife cuts more easily than a blunt side of it?
Answer:
A sharper side of knife has a smaller contact area. Therefore sharper side of knife exerts more pressure than the blunt side.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 1 Force

AP State Syllabus 8th Class Physical Science Important Questions 1st Lesson Force

8th Class Physical Science 1st Lesson Force 1 Mark Important Questions and Answers

Question 1.
What is force ? What is its S.I. unit?
Answer:
The push or pull of an object is called force. Its S.I. unit is Newton.

Question 2.
What is a contacting force?
Answer:
The force results when there is a direct physical contact between two interacting objects is called contacting force.

Question 3.
Define a force at a distance or field force.
Answer:
The force which occurs without any physical contact between two objects is known as force at a distance or field force.

Question 4.
What is muscular force?
Answer:
The force which we exert by using our body muscles is known as muscular force.

Question 5.
What is friction?
Answer:
The resistance to the movement of a body over the surface of another body is called friction.

Question 6.
Define normal force.
Answer:
The force that a solid surface exerts on any object in the normal direction is called normal force.

Question 7.
What is a magnetic force?
Answer:
The force exerted by a magnet on another magnet.

Question 8.
What is a gravitational force?
Answer:
The attractive forces between any two massive objects is called gravitational force.

Question 9.
What is electrostatic force?
Answer:
The force exerted by a charged body on other charged or uncharged body is called electrostatic force.

Question 10.
What is magnetic field?
Answer:
The space around the magnet where its influence can be detected is called magnetic field.

Question 11.
What is a net force?
Answer:
The algebraic sum of the forces acting on a body is known as net force.

Question 12.
What is free body diagram?
Answer:
The diagram showing all the forces acting on an object at a particular instant is called free body diagram.

Question 13.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
It changes the shape of iron.

Question 14.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad?
Answer:

1. The weight of the rocket downwards.
2. The upward force due to firing of rocket.

Question 15.
Why do not you experience gravitational force exists between you and your teacher because gravitational force depends on masses of object
Answer:
The reason is everything on earth experienced by a large gravitational force of earth so remaining gravitational forces are negligible.

Question 16.
What is tension?
Answer:
When we stretch a rope or a string the tightness of rope or string is called tension. Tension is a contact force.

8th Class Physical Science 1st Lesson Force 2 Marks Important Questions and Answers

Question 1.
Explain Gravitational Force by giving a suitable example.
Answer:
Gravitational Force: The force of attraction that exists between any two bodies (or masses) everywhere in the universe.
Examples:

1. The stone thrown up into the sky fall back on to the earth due to gravitational force.
2. Earth holding atmosphere due to gravitational force.
3. All the objects are pulling towards earth due to gravitational force.
4. Rivers flow down to the sea because of gravitational force.

Question 2.
The surface area of an object is 20 m² and a force of 10 N is applied on it, then what is the pressure?
Answer:
Force (F) = 10 N; Area (A) = 20 m × 2m = 40m²;
Pressure = \(\frac{F}{A}\) = \(\frac{10}{40}\) = 0.25 Pascal

Question 3.
Observe the situations of electrostatic forces in your daily life and prepare a report.
Answer:

1. If you comb your dry hair and bring small pieces of paper then these paper pieces are attracted by comb because it is charged.
2. If a glass rod is rubbed with a silk cloth then if we bring small pieces of paper near glass rod or silk cloth then these paper pieces are attracted by glass rod or silk cloth due to elctrostatic force.

Question 4.
Find the net force acting on a body shown in the figure. And draw the direction of net force. (Length of the arrow shows the magnitude of the force and direction also.)
Answer:

Question 5.
Give two daily life examples each of situations in which you push or pull to change the state of motion of object.
Answer:
Push:

1. Hitting a foot ball with your leg.
2. Moving a loaded cart.

Pull:

1. Opening a door
2. Moving a table towards you.

Question 6.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:

1. Pressing a sponge.
2. Stretching of rubber band.

Question 7.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Why do the forces acting on the bucket do not bring a change in its state of motion?
Answer:
The gravitational force acts as plastic bucket containing water held above ground level in your hand. Gravitational force does not bring change in state of bucket be¬cause equal amount of force is applied vertically upward.

Question 8.
Name the two forces acting on a rocket immediately after leaving the launching pad.
Answer:
The two forces acting on rocket are:

1. Force due to gravity vertically downward.
2. Frictional force of atmosphere.

Question 9.
What changes can be observed when we apply force on an object?
Answer:
a) Change in the shape of the object.
b) Change in direction of motion of an object.
c) Change in speed of an object if the object is moving.
d) Movement of an object from rest.

Question 10.
Have you ever seen a game of tug of war ? In this game two teams pull a rope in opposite direction. But sometimes the rope does not move explain why.
Answer:
a) When two forces acts on an object in opposite direction then the net force is difference of two forces.
b) If two teams pull the rope with equal force, the forces will be in opposite direction and will cancel with each other and the rope will not move.

Question 11.
How does an applied force change the speed of an object ?
Answer:

1. When force is applied in the direction of motion of object then the speed of object increases.
2. If the force is applied in the direction opposition to the motion of object then the speed decreases.

Question 12.
Give three examples of force exerted by muscles in our body.
Answer:

1. Blood circulation in our body.
2. Inhalation and exhalation of air by lungs.
3. Running by muscles of legs.

Question 13.
Why does the pointed end of the nail gets into wooden plank easily ?
Answer:
The area of pointed end of nail is much smaller than that of its head. The same force produces a sufficient pressure to push the printed end of the nail into the wooden plank.

Question 14.
Why do porters place a round piece of cloth on their heads?
Answer:
Porter place a round piece of cloth on their heads to increase the area of contact of the load with the head. So the pressure on their head is reduced and they can carry heavy load easily. .

Question 15.
On what factors does the effect of force depend?
Answer:
The effect of force depends on two things

1. The amount of force applied the more the force applied the greater the effect will be.
2. The area on which the force is applied. The smaller the area, the force is applied on the greater the effect will be.

Question 16.
How many types of forces are there and what are they? Give examples for each.
Answer:
Forces are two types:

1. Contact force e.g.: Muscular force, frictional force.
2. Force at a distance e.g.: Gravitational force, magnetic force.

Question 17.
What is pressure ? What is its unit?
Answer:
The force acting perpendicularly on a unit area of surface is called pressure.
Pressure = Force/Area
Its unit in S.I. system is Newton / metre or N/m .

Question 18.
What is the influence of Sir Isaac Newton on students?
Answer:

1. Everything we are discussing about motion and his contribution to mechanics and light one of the all time greatest scientist.
2. His experiments and laws, hypothesis influence the students to take up research and inspire them to become a future scientists of our nation.

8th Class Physical Science 1st Lesson Force 4 Marks Important Questions and Answers

Question 1.
Design and conduct experiment to test few ways how friction may be reduced.
Answer:
Friction is due to the roughness of surfaces. It can be reduced by the following methods.

1. By polishing the rough surface.
2. By applying lubricants like oil and grease to the surfaces.
3. By spreading powder on the rough surface like carromboard.
4. By using soap and detergent solutions, etc.

Experiment: The rusted pulley makes a rattling noise. Apply some oil in between the wheel and axle. The sound is reduced and now it works smoothly.

Question 2.
Collect pictures to illustrate contact forces, forces at a distance and prepare a report.
Answer:
I. Contact forces :
1) Muscular force:

2) Frictional force:

3) Normal force:

4) Tension:

II. Forces at distance (Field Forces)
1) Magnetic force:

2) Electrostatic force:

3) Gravitational force:

Report: Forces are two types based on contact or non-contact between objects.

I. Contact Forces : Force which results when there is a direct physical contact between two interacting objects is known as contact force. Contact forces are four types. They are :

1. Muscular Force: The force which we exert by using our body muscles is known as muscular force.
2. Frictional Force: Friction is the resistance to the movement of a body over the surface of another body.
3. Normal Force: The force that a solid surface exerts on any object in the normal direction is called normal force.
4. Tension: The lightness of slope or string when we try to stretch a rope or string is called tension.

II. Forces at distance (Field forces): The force which occurs without any physical con¬tact between two objects is known as a force at distance or field force.
Forces at distance are three types. They are:

1. Magnetic Force : The force existing between two magnetic poles of two different magnets is called magnetic force. The force is also exists between magnet and magnetic material.
2. Electrostatic Force : The force exerted by a charged body on another charged body is known as electrostatic force.
3. Gravitational Force : The force of attraction exists between any two bodies (or masses) everywhere in the universe is known as gravitational force.

Question 3.
When you push a heavy object, it doesn’t move. Explain the reason in terms of net force.
Answer:
There are four forces acting on the heavy table. They are normal force (upwards), gravitational force (downwards), push and friction (opposite to push).

Let’s take
Normal force = N (- ve); Gravitational Force = W (downwards); Push = F₁
Friction = F₂ (- ve) [more]
∴ Net force in X – direction = Push – Friction = F₁ – F₂ = – ve
Net force in Y – direction = N – W = – ve
As the net force in Y – axis is more you are unable to move the heavy object.

Question 4.
Some forces are acting without any contact of surfaces. Explain.
Answer:
Some forces like magnetic force, electrostatic force and gravitational force act on other bodies without any contact of surfaces. This property is called the field force.
As far as magnetic force concern, the magnets are surrounded by the magnetic lines of force which provide the magnets attractive and repelling forces. The same poles repel and the different poles attract.
The electrostatic forces are exerted by a charged body on another charged or uncharged body. The charged body induces an opposite charge on the uncharged body and it gets attracted by the body. Here, the two bodies are at distance before the electrostatic forces are exerted.
The earth attracts everybody even though they are at some distance. This force is called gravitational force or weight of the body. It varies at different places.

Question 5.
In the following situations identify the agent exerting the force and the object on which its acts. State the effect of force in each case.
a) A batsman hitting a cricket ball
b) Pressing a lump of dough
c) Taking out paste from a tooth paste
d) A horse pulling a cart
Answer:

Agent exerting force	Object on which it acts	Form of effect
Muscles	Cricket ball	Change in speed and direction
Fingers	Dough	Change in shape
Fingers	Tooth paste	Change in shape
Horse	Cart	Change in speed

8th Class Physical Science 1st Lesson Force Important Questions and Answers

Question 1.
A fruit is falling from a tree. Which force acts on the fruit?
Answer:
Gravitational force acts on the fruit, which is from a tree.

Question 2.
Find the net force from the following diagrams.

Answer:
a) Net force = + 12N + 10N – 8N = + 22N – 8N = 14 N
b) Net force = +9N – 8N = 1N

Question 3.
If you bring a rubbed balloon near the pieces of paper, what do you observe ?
Answer:
Rubber balloon attracts pieces of paper. It is electrostatic force.

Question 4.
From the above diagram, calculate the net force acting on a body.

Answer:
Net force in vertical direction = 5N – 5N = 0
Net force in horizontal direction = 10N – 8N = 2N

Question 5.
Find the net forces from the following free body diagram (FED).

Answer:
i) Net force in the vertical direction = + 6N – 6N = 0N
ii) Net force in the horizontal direction = + 20N – 3N = 17N.

Question 6.
What will happen if gravitational force disappears from the Earth? Explain.
Answer:
If gravitational force disappears from the earth,
i) No atmospheric gases are found around the earth.
ii) Objects does not fall down on the earth.
iii) Human beings, animals can fly easily in the sky.
iv) We cannot find the weight of the objects.

Question 7.
Define contact force and force at a distance, give two examples for each type of force.
Answer:
Contact force: The force results when there is a direct physical contact between two interacting objects is called contacting force.
Example: Muscular force, Frictional force, Normal force, Tension.
Field force or Force at a distance : The force which occurs without any physical contact between two objects is known as force at a distance or field force.
Example : Magnetic force, Electrostatic force, Gravitational force.

Question 8.
Using adjacent diagram, draw a free body diagram (FBD) to show the forces acting on the box.

Answer:

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 11 Some Natural Phenomena Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 11th Lesson Some Natural Phenomena

8th Class Physical Science 11th Lesson Some Natural Phenomena Textbook Questions and Answers

Improve Your Learning

Question 1.
Which of the following cannot be charged easily by friction?
A) A Plastic scale
B) A copper rod
C) An inflated balloon
D) A Woollen cloth
E) Piece of wood
Answer:
(B) A copper rod

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod
A) and the cloth both acquire positive charge.
B) becomes positively charged while cloth has a negative charge.
C) and the cloth both acquire negative charge.
D) becomes negatively charged while cloth has a positive charge.
Answer:
(B) becomes positively charged while cloth has a negative charge.

Question 3.
Identify ‘True’ or ‘False’ sentences among the following:
A) Like charges attract each other. (T/F)
B) A charged glass rod attract a charged plastic straw. (T/F)
C) Lightning conductor cannot protect a building from lightning. (T/F)
D) Earthquakes can be predicted in advance. (T/F)
Answer:
A) False
B) True
C) False
D) False

Question 4.
Sometimes, a crackling sound is heard while taking off sweater during winter. Explain.
Answer:
Charge is developed on the sweater because of friction. We can observe discharge of the charge while taking off the sweater which produce the crackling sound.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer:
The reason is that the charged object lose charge to the earth through our body that means it is transferred its charge to earth. The process of transferring of charge from a charged object to the earth is called earthing.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer:
The destructive energy of earthquake is measured in richter scale. Yes, it would be recorded by seismograph when earthquake measures 3 on the richter scale. It does not cause any damage to human life, generally we unable to felt its effect.

Question 7.
Suggest three measures to protect ourselves from lightning.
Answer:
Precautions to be taken to protect ourselves from lightning.

1. Staying in a house or building of low height.
2. If we are travelling in a bus or car, then we are safe inside the car or bus provided doors and windows are closed.
3. If we are in a forest taking shelter under shorter trees than taller trees is a good idea during the thunder storm.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by a charged balloon?
Answer:
A charged balloon is repelled by another charged balloon having same type of charge because both are having same kind of charges and like charges repel each other. Whereas an uncharged balloon attracted by a charged balloon because charged balloon induces opposite charge on uncharged balloon. We already know unlike charges attract each other. So the uncharged balloon is attracted by a charged balloon.

Question 9.
List three states in India where earthquakes are more likely to occur?
Answer:
The three states are

1. Jammu & Kashmir State (Mainly Kashmir)
2. Whole north east states like Tripura, Manipur, etc.
3. Rajasthan.

Question 10.
Does your habitation lie in earthquake prone area? Explain.
Answer:
Yes, my habitation lie in earthquake prone area because 1 am living in delta region of Krishna which is placed in seismic zone III. So it has chances of possibility of earthquake. (If the answering person is not living in Chittoor, YSR Kadapa, Nellore districts and Krishna and Godavari delta region then the answer is No.)

Question 11.
Which place in Andhra Pradesh experiences earthquakes most of the time?
Answer:
Badrachalam and Kothagudem are the places where there is a possibility of earthquake most of the time. Chittoor, Kadapa, Nellore and Krishna and Godavari delta region also have greater possibility of earthquake because they lie in zone-111.

Question 12.
When does a piece of matter have a “charge?”
Answer:
When a piece of matter rubbed with another piece of matter, the piece of matter acquire charge due to friction.
E.g.: Rub the refill vigorously with a piece of polythene and if we bring piece of paper that can be attracted by refill due to development of charge.

Question 13.
What happens if two objects having same charge brought close to each other? What happens if two objects having different charges are brought close? Can you give an example for this.
Answer:
Two objects having same charge repel each other and two objects having different charge attract each other.
E.g. A balloon rubbed with woollen cloth repelled by another balloon rubbed with woollen cloth because both will acquire same type of charge.
A balloon rubbed with a woollen cloth attracted by a refill rubbed with a polythene sheet because both will acquire different type of charge.

Question 14.
Give two examples of effects in your daily life caused by transfer of charges.
Answer:
Two examples in daily life:

1. Earthing
2. Lightning

Question 15.
Inflate two balloons and rub both of them with a cloth first and then with different material. Will they attract each other in both cases?
Answer:
No, they will not attract each other. Both will repel each other. The reason is both ballons rubbed with same material acquired same charge in the both the cases.

Question 16.
Which country in the world is frequently affected by earthquakes? Collect the information and photographs on the recent earthquake in Japan.
Answer:
The country in the world which frequently affected by earthquakes is Japan. Pictures of earthquake affected areas in Japan in 2012.
Photographs of earthquake:

Information about earthquake:

1. Lot of people killed due to earthquake.
2. Lot of people killed not only due to earthquake but tsunami caused by earthquake.
3. Lot of property loss took place.
4. Most of the people in Japan lost their jobs and livinghood.
5. They suffered emotionally also by losing their relatives, parents and children.
6. Lot of effect felt on their economy.
7. It effected the tourism of Japan.

Question 17.
Find out if there is an organization in your area which provides relief to those suffering from natural disaster. Enquire about the type of help they render to the victims of earthquake. Prepare a brief report on the problems of the earthquake victims.
Answer:
In India National Disaster Force provides relief for disaster victims.
Problems of earthquake victims:

1. Death: Many times, the people who support a family socially and economically dies. This causes most of the other members of the family to either fight their way through, or restart their lives from the bottom of the food chain.
2. Destroyed Structures: If the members of the family survive, then they could still be short of a home. The earthquake would have caused the destruction of their house and because of that, they would be left homeless.
3. No food or water: In the aftermath of an earthquake, people see whether all the pipelines, roads, etc. are in good shape or order. If the pipes are broken, then water scarcity begins. If the roads are broken, then food supplies cannot be transported, later causing problems in food scarcity.
4. Electricity : With inadequate supply of electricity, the debris and rubble will take a lot of time and if people are under it then they may die before the rubble is removed.
5. Illnesses: After the destruction of many buildings, the sewer pipes will also break and open, causing spread of disease everywhere.

Help render by relief organisation:

1. They minimize the death of people.
2. They provide drinking water and food for victims.
3. They provide shelter for earthquake victims.
4. They provide medical facility for earthquake victims.

Question 18.
How do you relate the energy release during the collision of fault lines during earthquake to the atmospheric variation on the surface of the earth?
Answer:
An earthquake effects the atmosphere by creating amounts of debris and dust which will add to the air that we breathe. Earthquakes can also trigger volcanoes which will release tonnes of ashes and other debris into the atmosphere. This can sometime cause the blocking out of the sun, air pollution and are increased amount of carbon in the air.

Question 19.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
The instrument used to detect a charged body is electroscope.
Description of Electroscope:
Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle. Pierce a hole in it, so that a metal paper clip could be inserted. Open out paper clip as shown in the figure. Cut two strips of aluminium foil about 4 x 1 cm each and hang them on the paper clip.

Insert the paper clip having the strips of aluminium foil into the cardboard lid so that it is perpendicular to it. This entire device works as a electroscope.
Procedure to detect a charged body ,by using a electroscope:
Charge a refill and make it touch the end of the paper clip. The aluminium foils move away from each other the reason that the strips of aluminium foil receive the same charge from the charged body through the paper clip and strips carrying similar charges repel each other and hence they move apart. This proves electroscope is useful in detecting a charged body.

Question 20.
Colour seismic zones in India out line map.
Answer:

Question 21.
Prepare a model of seismograph.
Answer:
Preparation of model:

Take a pendulum and which is attached to support. This acts as vibrating system. A pen is attached to this vibrating system. Place a rotating drum covered with a paper just below the pen. When earthquake occurs the pen records the seismic waves on a paper which move under it.

Question 22.
How do you appreciate the efforts of scientists to develop an instrument to assess the intensity and source of earthquake?
Answer:
The efforts of scientists to develop an instrument to assess the intensity and source of earthquake is thoroughly appreciated because they provide assessment of earthquake and what are the rescue measurements to be taken by government and private organizations and also provide preventive measurements that would be taken when earthquake occurs. So these scientists providing life for people and their services are thoroughly appreciated.

Question 23.
Suppose you are outside your home and an earthquake occurs. What precautions would you take to protect yourself?
Answer:

1. I find a clear spot, away from buildings, trees and over head powerlines and I drop to the ground.
2. If I am in a car or bus, I do not come out and I ask the driver to drive slowly to a clear spot. I do not come out of the car or bus till the tremors stop.

Question 24.
The weather department has predicted that a thunder storm is likely to occur at on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer:
No, I would not carry umbrella during thunderstorm because the metallic rod attached to the umbrella attracts the charge developed in thunderstorm and charge may carry through umbrella and possibility of electric shock. So it is not a good idea to carry umbrella during lightning.

Question 25.
If earthquake occurs in your area what will you do?
Answer:

1. I will protect myself by covering head with helmet or cushion and hide in a safe place, such as under table.
2. I will not run outside because roof tiles and glass may fall on me.
3. Major after shocks can come after smallest earthquake so I calmly extinguish any nearby flames.
4. Earthquake can wrap buildings, especially apartment buildings making it impossible to open doors and escape. So I open doors and windows to secure an escape route.
5. I will be careful with broken glass.
6. Once I come outside I will not return to house.
7. I will avoid phone calls.

Question 26.
What are the measures you would take in your house when an earthquake occurs?
Answer:

1. I would take shelter under a table and stay there till the shaking stops.
2. I would stay away from tall and heavy objects that may fall on me.
3. If I would be in the bed then I would not get up and I protect my head with a pillow.

8th Class Physical Science 11th Lesson Some Natural Phenomena Activities

Activity – 1

Question 1.
Effect of rubbing:

Take a used ball-pen refill and bring it near small pieces of paper.
The refill should be close enough but not touch the pieces of paper.
a) Check what happens to the paper pieces?
Answer:
They remain in the same position.
Now, rub the refill vigorously with a piece of polythene. Bring it close to small pieces of paper.

b) What is your observation. Take care that the rubbed end is not touched by your hand or with a metallic object.
Answer:
My observation is paper piece is attracted towards refill.
Now, take a comb and move it through dry hair a few times. Take the comb near small pieces of paper and check what happen.
The papers are attracted by comb.
Take an inflated balloon and rub it against your clothes. Bring the balloon close to small pieces of paper.
The paper pieces are attracted by balloon.
Take a drinking straw and rub it against a smooth wall or against your cloths, then bring it near pieces of paper.

c) What do you observe?
Answer:
The papers are not attracted by drinking straw.

d) Are they able to attract bits of paper after being rubbed?
Answer:
No, they are not attract bits of paper.
Repeat the activity by rubbing each one of the above mentioned objects (refill, comb, drinking straw, balloon) and use small pieces of dry leaf, husk, etc. as testing materials. Record your observation in table.

e) What can we infer from the above activity?
Answer:
When you rub material some material tend to attract pieces of paper.

f) Do objects like refill or comb attract pieces or paper only after rubbing?
Answer:
Yes, they attract pieces of paper only after rubbing.

g) Do all objects show this property?
Answer:
No, all the objects does not show this property.

h) Can we rub a comb against our palm and make it attract the paper bits?
Answer:
Yes, the paper bits are attracted to the palm due to friction charge is developed on the hand.

Lab Activity

Conduct an experiment of find the effects of charged bodies which have been rubbed by different materials.
Aim: To find effects of charged bodies which have been rubbed by different materials.
Materials required: A ball pen refill, a balloon, a comb, an eraser, a steel spoon, polythene sheet, plain paper, woollen cloth, etc.
Procedure:
Rub the above objects against materials listed in table. In each case, bring the rubbed object near small pieces of paper and note whether they attract pieces of paper or not. Record your observations in table by writing ‘yes’ or ‘no’.

a) What do you conclude from above table?
Answer:
Some objects like refill, comb when rubbed with specific materials able to attract light objects like bits of paper. But some objects like steel spoon do not attract pieces of paper even after rubbing.

b) Why don’t some materials attract pieces of paper even after rubbing ?
Answer:
The reason is some material acquire charge when we rub them and some may not acquire charge so they do not attract pieces of paper.

Activity – 2

Question 2.
Understanding types of charges:
Inflate two balloons and hang them in such a way that they do not touch each other. Rub both the balloons with woollen cloth and release them.

a) What do you observe?
Answer:
They repel each other. Take a refill and rub it with a polythene sheet. Keep it gently in a plastic tumbler. Take another refill and also rub it with the same polythene sheet.
Bring the second refill near the first one in the tumbler. Take care that you do not touch either of the rubbed portions on the refill with your hand.

b) Is there any effect on the first refill in the tumbler? Do they attract each other or repel each other?
Answer:
Yes, there is effect on the refill in the tumbler. They repel each other.

c) Now take a rubbed balloon near the rubbed refill in the tumbler and check the action. Do they attract each other or repel each other.
Answer:
They attract each other.
In the first two parts of the above activity, two objects that were made of the same material have brought near to each other after being rubbed with some appropriate material.

In the third part, objects made of different materials were brought near to each other after being rubbed with some material.
Let us summarise our observations carefully.

1. A balloon rubbed with woollen cloth repelled another balloon of the same type.
2. A refill rubbed with polythene repelled another refill rubbed with similar material.
3. A ballon rubbed with woollen cloth attracted by a refill rubbed with polythene sheet.

d) What can we conclude from these observations?
Answer:
Some charged objects are attracted and some charged objects are repelled with each other.

e) Does the repulsion between charged balloons indicate that they possess similar charge?
Answer:
Yes, they possess similar charge.

f) Does the attraction between charged balloon and a charged refill indicate that they possess different charges?
Answer:
Yes, they possess different charges.

g) Does this activity remind you some of experiments that you have done in “Playing with Magnets” Chapter of class VI?
Answer:
Yes, we know that magnets attract objects made up of magnetic materials like iron, nickel, cobalt, etc.
We also know that unlike poles magnet attract each other and like poles repel each other.

h) Can we say that something similar is happening in above activities?
Answer:
Yes.

i) Does it indicate that the charge on the balloon is of a different kind from the charge on the refill?
Answer:
Yes, it indicate they are different charges.

j) Can we say that there exist two kinds of charges?
Answer:
Yes, there exists two kinds of charges.

k) Can we also say that the charges of same kind repel each other, while charges of different kinds attract each other?
Answer:
Yes, it is convention to call the charge acquired by a glass rod when it is rubbed with silk cloth positive and charge acquired by a silk cloth is negative.
It is observed that when a charged glass rod is brought near a charged plastic straw which is rubbed with polythene sheet, there is attraction between the two.

l) What do you think about the kind of charge on the plastic straw?
Answer:
The plastic straw would carry negative charge.

m) Is your guess correct or wrong? Discuss with your teacher.
Answer:
My guess is correct because opposite charges attract each other which I confirmed by discussing with my teacher.

Activity – 3

Question 3.
Conduct an experiment to find out the presence of charge on a body.
Make a small ball of thermocol. Collect thin silver foil used to decorate sweets.
Wrap this thin silver foil to cover the thermocol ball and suspend it from a stand with the help of thread as shown in figure.

Bring a glass rod which is rubbed with a silk cloth near the suspended ball.
a) What happens ? Does it get attracted towards the glass rod or move away from it?
Answer:
It will attracts towards glass rod.
Now touch the silver foil on the thermocol ball with charged glass rod. Remove the glass rod from the ball and against rub it with silk cloth and bring it close to the suspended ball.

b) What do you observe?
Answer:
The suspended ball moves away from the glass rod.

c) What could be the reason for this change in movement of the ball?
Answer:
In the above activity when a charged body brought near an uncharged body it induces an opposite charge in it and hence it get attracted by the glass rod.
In the second case we have charged the thermocol by touching it with a charged glass rod. Hence when we brought the glass rod near the ball, as both of them have similar charge the ball gets repelled by the glass rod.
From the above activity we can conclude that attraction is not a sure test to know the presence of charge on a body.

Activity – 4

Question 4.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Take an empty jam bottle. Take a piece of cardboard slightly bigger in size than the mouth of the bottle.
Pierce a hole in it so that a metal paper clip could be inserted.

Open out paper clip as shown in the figure.
Cut two strips of aluminium foil about 4 cm x 1 cm each and hang them on the paper clip.
Insert the paper clip having the strips of aluminium foil in to the cardboard lid so that it is perpendicular to it as shown in the figure.
Change a refill and make it touch the end of the paper clip. Observe what happens.
a) Is there any effect on the strips of aluminium foil?
Answer:
Yes.

b) Do they repel each other or attract each other?
Answer:
They repel each other.

c) Now bring other charged bodies and make them touch the end of the paper. Do the foil strips behave in the same way in all cases?
Answer:
Yes, it behave in the same way in all cases.

d) Can this apparatus be used to detect the presence of charge on a body or not?
Answer:
Yes, it is used to detect the presence of charge on a body.

e) Can you explain why the strips repel each other?
Answer:
The strips of aluminium foil receive the same charge from the charged refill through the paper clip. The strips carrying similar charges repel each other and hence they move apart.
This device can be used to test whether an object is carrying charge or not. This device is known as electroscope. In the above activity you can observe that electric charge can be transferred from a charged object to another through a metal conductor.
Touch the end of the paper clip gently with hand and you will find a change in the foil strips they move closer and come back to their original state.

f) Why does it happen?
Answer:
The reason is that the foil strip lose charge to the earth through your body. We say that the foil strips are discharged.
The process of transferring of charge from a charged object to the earth is called earthing.

Activity – 5

Question 5.
Collecting information about the damages caused by earthquakes:
Ask your parents about the huge damages to life and property caused by these earthquakes. Collect a few pictures showing the damage caused by these earthquakes from newspapers and magazines of those days.
Prepare a short report on the suffering of the people during the earthquakes.
Answer:
Report: It caused damage to human life and property on a hugescale. Due to tsunami thousands of people died in the coastal areas of Andhra Pradesh and Tamilnadu. People lost their shelter.
a) What is an earthquake?
Answer:
An earthquake is a sudden shaking or trembling of earth lasting for a very short period of time. It is caused by a disturbance deep inside the earth’s crust.

b) What happens when it occurs?
Answer:
When it occurs it can cause damage to human life and property on a huge scale.

c) What can we do to minimize its (earthquake) effects?
Answer:
People living in seismic zones, where the earthquakes are more likely to occur, have to be specially prepared. The buildings in these zones should be designed so that they can with stand major tremors.
Steps to be taken in building construction:

1. In highly seismic areas, the use of mud or timber is better than heavy construction material.
2. Keep roofs as hieght as possible. In case the structure falls, the damage will not be heavy.
3. It is better if the cupboards and shelves are fixed to the walls so that they do not fall easily.
4. Be careful where you hang wall clocks, photoframes, water heaters, etc. so that in the event of earthquake, they do not fall on the people.
5. Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings have fire fighting equipment in working order.

Measures to be taken in a house when earthquake occurs.

1. Take shelter under a table and stay there till shaking stops.
2. Stay away from tall and heavy objects that may fall on you.
3. If you are on bed, do not get up. Protect your head with a pillow.

Measures to be taken outdoors when earthquake occurs.

1. Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.
2. If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out till the tremors stop.

Activity – 6

Question 6.
Locating the tsunami affected areas in the map:
Take an outline map of the world. Locate the eastern coast and Andaman and Nicobar Islands in India. Mark other countries around the Indian Ocean which could have suffered damage.
Collect accounts of the devastation caused by the tsunami in India from your parents, or other elders in the family or in the neighbourhood.
Answer:

Devastation due to tsunami:

1. Loss of lives, families and friends.
2. Loss of properties.
3. Loss of jobs and living.
4. Emotional challenge.
5. Loss of livestock.
6. Dramatic or drastic changes to a whole community’s routine living.
7. Negative impact on the affected regions, economy.
8. Negative impact to the affected region’s tourism.

To the environment:

1. Alternation to seaside terrain.
2. Minor deforestation in the area effected by the tsunami.
3. Wild life casualities.
4. The sea will be temporarily littered with debris after the tsunami.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 4 Synthetic Fibres and Plastics Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 4th Lesson Synthetic Fibres and Plastics

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics Textbook Questions and Answers

Improve Your Learning

Question 1.
Explain why some fibres are called synthetic.
Answer:
Unlike natural fibres, synthetic fibres are made from petroleum based chemicals or petrochemicals. Petrochemicals are subjected to various chemical processes to obtain synthetic fibres. Due to this they are called artificial fibres or synthetic fibres.

Question 2.
Give reasons why plastic containers are used as storage devices.
Answer:
Plastic containers are used as storage devices because

1. They are non-reactive: Metals like iron get rusted when they left exposed to moisture and air. But plastic do not react with water and air. So they are not corroded easily.
2. Plastic is light, strong and durable: Plastics are very strong, light and durable can be moulded into different shapes.
3. Lower price: Plastics have relatively lower price when compared with metals.

Question 3.
Classify following materials which can be, cannot be recycled.
Plastic toys, electrical switches, plastic chairs, ball point pens, plastic containers, cooker handles, plastic bottles, carry bags, tumblers, tooth brush, plastic chapels, plastic plates, plastic buckets.
Answer:

Plastic toys	–        recycled
Plastic chairs	–        recycled
Ball point pens	–        not recycled
Tooth brush	–        not recycled
Cooker handles	–        not recycled
Plastic containers	–        recycled
Plastic bottles	–        recycled
Carry bags	–        not recycled
Tumblers	–        recycled
Electrical switches	–        not recycled
Plastic chapels	–        recycled
Plastic plates	–        not recycled
Plastic buckets	–        recycled

Question 4.
If electric switches are made by thermoplastics what would happen?
Answer:
Thermoplastics are become soft on heating and they can change their shape. Heat developed due to electricity may change the shape of switches and they become soft whereas thermosetting plastics once moulded does not change their shape and they comparatively bad conductors of heat and electricity than thermoplastics. So thermo-plastics are not preferable in making of electrical switches.

Question 5.
Thermoplastics are ecofriendly than thermosetting plastics. What do you say? Why?
Answer:
Yes, they are ecofriendly when compared with thermosetting plastics. The reason is plastics are non-biodegradable material. Land filling of plastic and burning of plastic in incenerators are the ways of disposal of plastic. These two ways are harmful to environment. The better method is recycling of plastic. Which is possible with only thermoplastics and thermosetting plastics cannot be recycled. Therefore we consider thermoplastics as ecofriendly.

Question 6.
Explain the following.
a) Blending
b) Biodegradable
c) Recycling
d) Decomposition
Answer:
a) Blending: Any synthetic fibre can be combined with two or more other fibres is called blending. Natural and synthetic fibres are often blended for preparing better fabric.
When first fibre is blended with second fabric it gives us a blended fabric which possess the best quality of both.
Eg: We know cotton wearing is comfortable and polyester is wrinkle free. When cotton and polyester blend the end result of fabric formed is comfortable and wrinkle free.

b) Biodegradable: A material which is easily decomposed by natural process is called biodegradable. Eg: Vegetables, fruits, paper, cotton, clothes, woolen clothes, etc.

c) Recycling: Recycling is a process of conversion of broken plastic material into new plastic products.

d) Decomposition: Certain materials can break down in to smaller fragments in the presence of water, sunlight and oxygen. These fragments get further broken down by bacteria. This is called decomposition.

Question 7.
Match the following.
Group – A                              Group – B
1. Polyester        ( )          A) Kitchenware
2. PET                 ( )          B) Artificial silk
3. Rayon             ( )          C) Many monomers
4. Nylon             ( )          D) Electric switches
5. Melamine       ( )          E) Code 1
6. Polyethene     ( )          F) Popular dress material
7. Bakelite          ( )          G) Stronger than any fiber
Answer:
1) F
2) E
3) B
4) G
5) A
6) C
7) D

Question 8.
Fill in the blanks.
i) Synthetic fibres are called as …………….. fibres.
ii) Synthetic fibres are synthesized from raw material called ……………. .
iii) Like synthetic fibre, plastic also ……………… .
iv) Clothing labels are
A) Required by law
B) Identify fabric content
C) Both A and B
D) None of the above
v) Rayon is made of
A) Coal
B) Oxygen
C) Flax
D) Cellulose
vi) A silk fibre’s smooth surface absorbs light
A) Yes
B) No
C) Can’t say
Answer:
i) artificial
ii) petrochemicals
iii) Polymer
iv) B) Identify fabric content
v) D) Cellulose
vi) B) No

Question 9.
Where do we use the process of recycling? How is it useful? Give examples.
Answer:
The process of recycling is useful for plastic which are non-biodegradable material. The broken plastic material articles collected from the households and send it for recycling. From this recycled plastic new products are prepared after giving it a proper treatment.
e.g.: Pet bottles, plastic carry bags, coffee cups, egg boxes.

Question 10.
Prepare a table of various synthetic fibers which are used to make household articles from them.
Answer:

Synthetic fibre	Household item
Nylon	It is used in most hosiery articles such as stockings. Also tooth brush bristles, ropes, tents, sarees, socks, car seat belts, sleeping bags, curtains, carpets, fishing nets, etc.
Synthetic fibre	Bead necklace, paper clip, paper clip, chain, etc.
Rayon	It is used to prepare sarees, bed sheets, carpets, fashion and home furnishings, sanitary products, diapers and bandages and lints for dressing wounds, etc.
Acrylic	It is used in knitted apparels such as fleece, socks, sportswear and sweaters. It is also used in craft yarns, upholstery fabrics, carpets, luggage awnings and vehicle covers, etc.
Polyesters	Polyester is used to make dresses, PET bottles, utensils, fibres, wires etc.
Polyesters	Polyester is made by reacting dicarboxylic acid with dihydric alco­hol.
Nylon	Nylon is made of chemical units called polyamides (carbon, oxygen, nitrogen)
Rayon	The cellulose collected from plants is treated with sodium hydrox­ide, carbon disulphide and into dilute sulphuric acid.
Acrylic	It is made from the combination of coal, air, water, oil and limestone.

 

Question 11.
Explain the differences between the thermoplastics and thermosetting plastics with the help of a diagram explaining in terms of arrangements of monomers.
Answer:

Question 12.
Introduction of synthetic fibres in the textile industry brought revolutionary change across the world in the dressing patterns irrespective of culture and customs. How do you appreciate this?
Answer:
Synthetic fibres are used everywhere in the world due to their specific characteristics that is they are durable, less expensive, readily available, affordable and are easy for maintenance. So they are decreasing the boundaries of races. So synthetic fibres are one of the factor which make the people unite irrespective of culture and costumes.

Question 13.
How synthetic fibres changed our everyday life?
Answer:
Synthetic fibres are more comfortable and wrinkle free. They does not shrinks. They exists in different colours. They are less expensive. They absorb less water and dry at a faster rate. They exists in different designs. They are durable and readily available. Different synthetic fibre clothes are available for different seasons. Now synthetic fibres are essential part of our life. So synthetic fibres changed our life.

Question 14.
Nibha wants to buy clothes to parents for winter wear. What type of clothes would you suggest? Specify reasons.
Answer:
We would suggest clothes made of acrylic. The reason is it is affordable and accessible. It is cheap and easily available. It has all the characteristics of wool so considered as artificial wool. So it is preferable to wear clothes made of acrylic in winter.

Question 15.
If plastic is not properly disposed, what could be the consequences?
Answer:
Plastics take several years to decompose. Slow decomposition of plastics causes environment pollution. The polythene bags thrown around are responsible for clogging drains. The animals in urban areas are dying due to eating of polythene bags containing food material. They not only posed a great threat to nature and environment but also to the human race itself. The burning process of plastic is also very slow and cannot be burnt completely. The process of burning release a lot of poisonous fumes in to air causing air pollution. So plastics should be properly disposed that is recycling process is used.

Question 16.
Indiscriminate usage of plastic is a serious threat to bio-diversity. What are the efforts of government and non-government organization in this regard?
Answer:
Efforts of government and non-government organisation:

1. Andhra Pradesh based NGO’s drawing court attention that 30 – 60 kg of plastic bags recovered from the stomache of cows.
2. Private institutions in Kozikode, Kerala fighted against plastic wastes and their consequences on environment.
3. Government has burned plastic carry bags less than 40 microns.
4. Many non-government organisations are giving publicity about the harmful effects of plastics. They are encouraging people to use bags made of cotton.
5. Various non-government organisations are collecting plastics from households and send it for recycling.
6. Government is planning to solid plastic waste into resources such as electricity, heat, compost.

Question 17.
Take hair, wool, silk, paper, cotton thread, piece of plastic, thread of sweater, piece of rope and carefully conduct a flame test. Based on smell and type of melting classify them as natural or artificial fibres.
Answer:
If they burn with black deposit of carbon then the fibres are natural. If they melt they are artificial fibres.

Fibre	Natural / Artificial
1. Hair	Natural
2. Wool	Natural
3. Silk	Natural
4. Paper	Natural
5. Cotton thread	Natural
6. Piece of plastic	Artificial
7. Thread of sweater	Natural
8. Piece of rope (Plastic)	Artificial

Question 18.
Prepare a chart which can explain recycling codes, full name and acronym of plastic and its usage for various household articles, recycled or not, if recycled what will be made from that?
Answer:
Recycle code symbols:

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics InText Questions and Answers

8th Class Physical Science Textbook Page No. 45

Question 1.
Are all of our clothes made of natural fibres?
Answer:
No, there are two types of fibres. They are natural fibres and synthetic fibres. Nowadays we make up artificial fibres from natural fibres by adding petroleum products.

8th Class Physical Science Textbook Page No. 46

Question 2.
What do you know about synthetic fibres? How are they manufactured?
Answer:
The artificial fibres obtained from plant or animal source are called synthetic fibres. They are made by the raw materials obtained from petroleum, e.g.: Polyester, nylon and acrylic.

Question 3.
What does polymer mean?
Answer:
The word polymer was derived from Greek. Poly means many and mer means part/unit.

8th Class Physical Science Textbook Page No. 53

Question 4.
Why are soft drinks stored in PET bottles?
Answer:
Soft drinks are carbonated so they are stored in PET bottles which are non-reactive with carbonated drinks.

Think and Discuss

8th Class Physical Science Textbook Page No. 46

Question 1.
What made the human beings to search for the alternative for natural fibres?
Answer:
Human beings used to wear clothes made by natural fibres like cotton, wool, silk, etc.
They do not have uniform thickness, they are costly, less durable, not readily avail¬able, they are not wrinkle free, they do not have water proof, they are not lustrous. So in order to avoid these advantages of natural fibres human beings made search for alternative for natural fibres.

Question 2.
Which fibre source is not exhaustible? Why?
Answer:
Natural fibre source is not exhaustible because they are made from plants and animals. Where as artificial fibres are made from petrochemicals which are exhaustible.

8th Class Physical Science Textbook Page No. 47

Question 3.
How synthetic fibres evolved to the present position?
Answer:
Synthetic fibres are cheap, durable, readily available, wrinkle free, they are affordable and easy maintenance made them to evolve the present position.

8th Class Physical Science Textbook Page No. 49

Question 4.
If we use cotton cloth and cotton ropes in preparing a parachute, what will happen?
Answer:
Cotton thread does not resist to higher weights. So the rope breaks. So it is not preferable to use cotton cloth and cotton rope in preparing parachutes.

Question 5.
Traditionally fishermen used cotton nets. Now they are using nylon nets. What is the advantage of using nylon nets?
Answer:
Cotton does not resist to higher weight and it is not strong. It is easily breakable with small weights. So nowadays fisherman are using nets which are made of nylon which resist to higher weights and are strong.

Question 6.
Nylon sarees are much better than the cotton sarees. It is better to use only nylon sarees. Do you agree with this ? Why?
Answer:
Nylon fibre is strong, elastic and light weight. Cloth made of nylon are lustrous and easy to wash. Nylon does not absorb water. So in general nylon clothes are better than cotton clothes but it has some limitations that is static electricity is easily created in nylon fabric. It also easily catches to fire and nylon clothes stick to human body so we should not wear nylon clothes while cooking, welding or working near a fire or using heavy machineries. So wearing nylon sarees always is not preferable.

8th Class Physical Science Textbook Page No. 50

Question 7.
What characteristics make rayon better than natural silk?
Answer:
Artificial rayon is cheaper than silk and can be woven like silk fibre. It can be dyed in a wide variety of colours. So artificial rayon is better than natural silk.

Question 8.
If you want to purchase a doormat made of synthetic fibre, which synthetic fibre doormat will you select? Why?
Answer:
We would prefer nylon for door mats because it is strong, elastic, cheap, easy to wash, does not absorb water and lustrous.

Question 9.
If sanitary diapers and bandages are made up of nylon, what will happen?
Answer:
Nylon fibres are strong. So they are difficult to cut. So they are not preferable for sanitory diapers and bandages.

8th Class Physical Science Textbook Page No. 51

Question 10.
Which type of blended fabrics do you find more comfortable in winter? Why?
Answer:
We would find terriwool are more comfortable in winter. The reason is terriwool is similar to wool so protect us from cold.

Question 11.
The fabrics namely natural, synthetic and blended are available for garments. Which fabrics will you prefer to wear for rare occasions like functions and in routine? Why?
Answer:
We will prefer to wear blended fabric in rare occasions like functions because it possess best qualities of natural and artificial fibre. Generally we will prefer artificial fibre because it is cheap, durable and easily available.

8th Class Physical Science Textbook Page No. 52

Question 12.
Which fabric do you prefer? Natural or synthetic? Why? Discuss comparatively.
Answer:
We would prefer synthetic clothes generally because they are durable, less expensive, readily available, affordable, they absorb less water and dry at faster rate, they are lustrous and they are easy for maintenance. But we would not prefer for synthetic clothes for those who are working in the kitchens and laboratories. The reason is synthetic fibres are easily catch fire and the fabric melts and sticks to the body of the person who wears it.

Question 13.
What is the difference between washing of clothes at home and washing by dry cleaning at laundary?
Answer:
At home for washing of clothes we use detergent or washing powder and water. Whereas dry cleaning is the process conducted in the absence of water for those clothes which should not be washed with water. So in laundry dry cleaning is carried out by using organic liquids like petrol, benzene, acetone, etc.

8th Class Physical Science Textbook Page No. 57

Question 14.
Certain fry pans are said to be non-stick. What made them as non-stick?
Answer:
Teflon is special plastic on which oil and water do not stick. It is used for non-stick coating on cookwares.

Question 15.
Firemen wear dress which does not catch fire. What type of fabric it is made of?
Answer:
Melamine is a plastic which is fire resistable and flame resistant is used to make the dress of firemen.

8th Class Physical Science 4th Lesson Synthetic Fibres and Plastics Activities

Activity – 1

Question 1.
Identify household articles made up of natural and synthetic fibres.
Identify the articles around you in your surroundings and write their names against relevant category in the table.
Answer:

Source	Articles
1. Natural fibres from plants	Cotton saree, dresses, curtains, kerchiefs.
2. Natural fibres from animals	Silk clothes, Woolen clothes.
3. Synthetic fibres	Nylon clothes, rayon clothes, polyester clothes, plastic chairs, plastic carry bags, electric switches, plastic bottles, T.V. cabi­nets, etc.

Activity – 2

Question 2.
Beads and paper clips pattern.
Take a few paper clips and join together as shown. Observe the pattern of clips.

a) Do you find any similarity between the pattern of beads in necklace and the pattern of paper clips in the chain.
Answer:
Yes, each unit of paper clips or beads can be joined together to form a long chain structure.

b) What happens if small unit of chemical substance is combined together?
Answer:
It forms a large unit of polymer.

c) How does we obtain synthetic fibres?
Answer:
Synthetic fibres are obtained from polymers.

d) What are the source of synthetic fibres?
Answer:
Petrochemicals.

Activity – 3

Question 3.
Identifying fibres – burning test
You can do a fibre burning test. Unravel several wrap and weft yarns. Using tweezers hold the yarn to the edge of a flame. Observe, the changes.
a) If it smells like burning hair, what is the yam is wool or silk?
Answer:
It is wool or silk.

b) If it smells like burning paper, what is the yam?
Answer:
The yarn may be cotton or rayon.

c) If the yam melts in the flame, what is the yam?
Answer:
The yarn is synthetic fibre such as nylon and acrylic.

Activity – 4

Question 4.
How strong is nylon?

Take an iron stand with a clamp. Take cotton, wool, nylon and silk thread about 50 cm in length. Tie cotton thread to stand so that it hangs freely from it. At the free end, attach a pan so that a weight can be placed on it. Add weight starting from 10 grams one by one till the thread breaks down. Note down the total weight required to break the thread. Repeat the same activity with threads of wool, silk and nylon.

a) Arrange the thread in the order of increasing strength.
Answer:
Cotton < Wool < Silk < Nylon

b) Do you know that if you compare nylon thread with a steel wire of same thickness, nylon will be as strong as steel wire?
Answer:
Yes, it is the strongest man made fibre.

Activity – 5

Question 5.
Why do we combine fibres?
a) Whenever you buy clothes or ready made garments observe the brand label. What do you notice?
Answer:
There is some information about cloth is written on the brand label.

b) What do you see?
Answer:
We can see quality, shade no, width, contents and wash care of the cloth.

c) What is the percentage of fibres?
Answer:
40% polyester and 60% cotton.

d) Why do we combine fibres? What is the process called?
Answer:
We would combine two fabrics to get a fabric which has best qualities of both. This process is called blending.

Activity – 6

Question 6.
How can you say a bottle is PET bottle?
Collect different kinds of water bottles of your classmates and look at them carefully.
a) Do you observe any triangle shaped symbol at the bottom of the bottle or on the brand label of the sticker?
Answer:
Yes.

b) What number is marked at the center of the triangle?
Answer:
I had observed number 5.

c) If code no. is 1 what it indicates?
Answer:
It indicates PET bottle.

Activity – 7

Question 7.
Identification of various articles with recycling codes.
Collect bottles of soft drinks (500 ml or more), bottles of juice and containers of fruit jam, Ketchup, shampoo, coffee powder and try to look for the triangle. You can also go to the near by shop and request the shopkeeper show you the bottle.
a) What are these codes?
Answer:
These are recycling codes of various types of plastic material.

b) What is the use of these codes?
Answer:
We can identify what kind of material is used for the preparation of article by seeing the code at the bottom of the article.

c) Are all bottles found with codes?
Answer:
Yes, all bottles have codes.

d) What code is observed for soft drinks and juices?
Answer:
We can observe code T marked in the middle of triangle.

e) What about Boost or Boumavita bottles?
Answer:
We can observe code 5 marked in the middle of triangle which tells us the bottle is made up of polypropylene.

Activity – 8

Question 8.
Types of plastics.
Let us take two bottles made up of plastic. One is PP bottle and another ordinary (PET) Pour some hot water in both.

What do you notice?
Answer:
The ordinary bottle get deformed.

a) What is the code of the deformed bottle?
Answer:
Code No. 2.

b) What is the name given to plastics which are deformed easily on heating?
Answer:
Thermoplastics.

c) What is the name given to plastics which are molded once can’t be s heating?
Answer:
Thermosetting plastics.

d) Can you tell Topper ware is thermosetting plastic or thermo plastic?
Answer:
Thermosetting plastic.

Lab Activity

Identify whether given plastic material is thermoplastic or thermosetting plastic by using flame test. (OR)
Conduct a flame test to identify thermoplastics and thermosetting plastics. (OR)
You are given a comb, tooth brush handles, plastic bucket, handle of utensil, Electric switch, piece of melamine of meals plate and coffee mug. Explain how can you identify which object is a thermoplastic or thermosetting plastic through an activity.
Answer:
Aim: Identifying thermoplastics and thermosetting plastics by flame test.
Material required: Pair of tongs, spirit lamp, samples of plastics (pieces of comb, tooth brush handle, plastic bucket, handle of utensil, electric switch, piece of melamine of meals plate and coffee mug).
Procedure:

1. Take a spirit lamp and light it.
2. Clamp one piece of plastic sample say piece of tooth brush with tong.
   
3. Place the sample on spirit lamp flame.
4. Observe the changes during the burning of sample.
5. Note your observations like, whether sample is being softened or burnt with smell or become hard, etc.
6. Repeat the procedure with other samples.
7. Record your observations sample wise in the table.
   

   Name of the plastic sample	Softened / burnt with burning smell and become hard	Thermoplastic/ Thermosetting plastic
   Tooth brush handle	Softened	Thermoplastic
   Comb	Softened	Thermoplastic
   Piece of bucket	Softened	Thermoplastic
   Handles of utensil	Burn with burning smell and become hard	Thermosetting plastic
   Electric switch	Burn with burning smell and become hard	Thermosetting plastic
   Meals plate	Softened	Thermoplastic
   Coffee mug	Softened	Thermoplastic

Activity – 9

Question 9.
Biodegradable – Non-biodegradable:
Let’s take peels of fruits and vegetables, left over food stuff, waste paper, cotton cloth and plastic bag. Keep this material in a pit. Open the pit after some days and list the material which remain a long time and those that disappear quickly.

Type of waste	Approximate time to disappear	Change
1. Peels of fruits and vegetables	1 to 2 weeks	degradable
2. Left over food stuff	1 to 2 weeks	degradable
3. Waste paper	10 to 30 days	degradable
4. Cotton cloth	2 to 5 months	degradable
5. Plastic bag	Several years	non-degradable

a) What is the name given to certain material which can be break down into smaller fragments in the presence of water, sun light and oxygen and by bacteria?
Answer:
Biodegradable.

b) What do we call the material which are not decomposed by natural process?
Answer:
Non biodegradable.

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 4 Reproduction in Animals

AP State Syllabus 8th Class Biology Important Questions 4th Lesson Reproduction in Animals

8th Class Biology 4th Lesson Reproduction in Animals 1 Mark Important Questions and Answers

Question 1.
What is meant by external fertilization?
Answer:
The process of fertilization that occurs outside of an organism is called External Fertilization. E.g.: Frog, Fish, Star fish etc.

Question 2.
What is meant by Internal Fertilization?
Answer:
The process of fertilization that takes place inside the body of females is called Internal Fertilization. E.g.: Animals, Human beings.

Question 3.
Which are called Viviparous animals?
Answer:
Animals which give birth to their offsprings are called Viviparous animals. E.g.: Animals, human beings.

Question 4.
What are oviparous animals?
Answer:
Animals which lay eggs are called oviparous animals.
E.g. Hen, Duck, Pigeon etc.

Question 5.
Which is formed by the fusion of male and female gametes?
Answer:
Zygote is formed by the fusion of male and female gametes.

Question 6.
Which gamete is that has a tail and travel to fuse with female gamete?
Answer:
Male gamete or sperm or spermatozoa. The structure of sperm has a head, a middle piece and a tail.

8th Class Biology 4th Lesson Reproduction in Animals 2 Marks Important Questions and Answers

Question 1.
Complete this flow chart.

Answer:
1 – Testes
2 – Sperms
3 – Ovary
4 – Ovum
5 – Embryo
6 – Foetus

Question 2.
What is meant by cloning if Who invented this?
Answer:

1. Cloning is the reproduction of an exact copy of the cell, any other living part or complete organism from somatic cells.
2. Cloning of an animal was successfully performed for the first time by lan Wilmut in Scotland.

8th Class Biology 4th Lesson Reproduction in Animals 4 Marks Important Questions and Answers

Question 1.
Complete the cross word puzzle using the hints given below.
Across:
1. The process of the fusion of the gametes.
6. The type of fertilization in hen.
7. The term used for bulges observed on the sides of the body of Hydra.
8. Eggs are produced here.
Down:
2. Sperms are produced in these male reproductive organs.
3. Another term for the fertilized egg.
4. These animals lay eggs.
5. A type of fission

Answer:

Question 2.
Write a note on “test tube babies”.
Answer:

1. The babies who born through IVF (In Vitro Fertilization) technique are called “Test tube babies”.
2. In some women, oviducts are blocked due to some reasons. In these cases fertilization will not takes place. Doctors collect freshly released egg and sperms and keep them for few hours.
3. In case, fertilization occurs, the zygote is allowed to develop for about a week and then it is placed in the mother’s uterus.
4. Babies born through this technique are called ‘Test tube babies’ which does not mean babies growing in test tubes.

8th Class Biology 4th Lesson Reproduction in Animals Important Questions and Answers

Question 1.
What are Oviparous and Viviparous animals ? Write their characters and give some examples.
Answer:

1. The animals giving birth to their off springs are called Viviparous animals.
2. The animals which lay eggs are called Oviparous animals.
3. Viviparous animals have epidermal hair on their skin and external ears. Examples are cow, elephant, dog, etc.
4. Oviparous animals do not have epidermal hair or external ears. Examples are fish, frog, crow, peacock, snake, lizard etc.

Question 2.
Kshitija found a fish like larva and put it in an aquarium supposing it as a fish. What would she find after some days?
Answer:

1. Kshitija had brought tadpole larva, which looks like a fish. It was the larva of the frog.
2. After somedays, this tadpole larva undergoes metamorphosis and develops into a frog.
3. Hence, Kshitija would observe a frog in place of tadpole larva after some days in the aquarium.

Question 3.
You want to clarify some doubts about test tube babies what questions do you ask the doctor?
Answer:

1. Where do test tube babies born?
2. What differences may we find between normally born baby and a test tube baby?
3. What problems will test tube babies face in their life?
4. Why people have so many doubts about test tube babies?

Question 4.
Draw a neat labelled diagram of a human sperm. Fill the following table:

Name of the organ	Function
Tail
Mitochondria
Head
Middle piece

Answer:

Name of the part	Function
Tail	Helps in the movements of the sperm.
Mitochondria	Releases energy for the movements of the sperm cell and also provides energy for the penetration of sperm into Ovum.
Head	Helps in the process of fertilization.
Middle piece	It is the site of mitochondria which are the power houses of the cell.

Question 5.
Latha draw the following flow chart of Human reproduction like this. Is it correct or not.
If not, draw a correct one.

Answer:

Question 6.
What are the differences you observed in the reproduction of Amoeba and frog?
Answer:

Reproduction in Amoeba	Reproduction in Frog
1. Asexual mode of reproduction takes place in Amoeba.	1. Sexual mode of reproduction takes place ts Frog.
2. Fusion of garnets will not occur.	2. Fusion of garnets takes place.
3. Through binary fission or multiple fission (during unfavourable condi­tions) daughter amoebas are formed.	3. Through external fertilization, many offsprings will take birth in water.
4. Daughter amoebas formed during binary fission, completely resemble their mother.	4. Offsprings formed exhibit variations.
5. Mother Amoeba will extinct sifter binary fission.	5. Mother frog will not extinct after external fertilization.

Question 7.
Write the apparatus used in the project work of observing the life cycle of frog.
Answer:
To conduct this project we need,

1. Wide mouth transparent bottle/tube
2. Transparent glass
3. Dropper
4. Petridish
5. Some pebbles
6. Magnifying glass

Question 8.
Fill in the blanks with the correct terms.
The main male reproductive organs are A and in females are B. A and B release some cells respectively known as C and D. The fusion of C and D is known as E. E results in the formation of F. F gradually develops into a G and finally becomes a H.
Answer:
The main male reproductive organs are Testes and in females are Ovary. Testes and Ovary release some cells respectively known as Sperm cells and Ova. The fusion of Sperm cells and Ova is known as Fertilization. Fertilization results in the formation of Zygote. Zygote gradually develops into a Embryo and finally becomes a Foetus.

Question 9.
Observe this diagram and answer the questions.

a) The diagram belongs to which system?
b) Write the A, B, C in the above diagram.
c) What produces the “B” part?
d) What is function of Part “A”?
Answer:
a) Male reproductive system in human beings.
b) A – Seminal ducts B – Testes C – Penis
c) Sperm cells
d) This duct connects each testes to the urethra. They transport sperms into the penis.

Question 10.
Look at the picture and answer the questions.

a) Which system does the picture belong to?
b) What is “A”? What is produced here?
c) What is “B”?
d) What happens when fallopian tubes are closed?
Answer:
a) Female reproductive system in human beings.
b) Ovary
c) Uterus
d) Fertilization will not take place.

Question 11.
What happens to a female body when ovulation stops forever?
Answer:
a) If ovulation stops in females, menstrual changes do not occur in female body. This stage is known as ‘menopause’.
b) As ovum is not released, there is no chance of pregnancy in this stage.

Question 12.
Label the parts of female reproductive system and answer the following questions.

a) In which part of the female reproductive system does fertilization occur?
b) What is the function of the part labelled as 2?
Answer:
Labelled parts :

1. Fallopian Tube
2. Ovary
3. Uterus
4. Fallopian tube
5. Releasing ova

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 9 Production and Management of Food From Animals

AP State Syllabus 8th Class Biology Important Questions 9th Lesson Production and Management of Food From Animals

8th Class Biology 9th Lesson Production and Management of Food From Animals 1 Mark Important Questions and Answers

Question 1.
From where do we obtain food?
Answer:
We obtain food from plants and animals.

Question 2.
What are the food items that are obtained from animals?
Answer:
We obtain milk, meat and eggs from animals.

Question 3.
What is animal husbandry?
Answer:
Providing food, shelter, protection and breeding of animals is called animal husbandry.

Question 4.
How did man use animals since long time?
Answer:
Since long time, man used animals not only for obtaining food but also for agriculture, transportation etc.

Question 5.
Why did early man domesticate only some of the animals?
Answer:
The early man domesticated only some of the animals which provide him food, clothing and the animals which are helpful for agriculture and transportation.

Question 6.
In what way the animals are useful to us?
Answer:
Buffalo and cow give us milk, hens give us eggs and meat, goats and sheep provide us meat, ox, bulls, donkeys are useful for agriculture and transportation.

Question 7.
What do farmers believe in our country?
Answer:
In our country farmers believe that animal husbandry is part and parcel of agriculture.

Question 8.
Name the animals that domesticate by the people living in rural areas.
Answer:
People living in rural areas domesticate animals like cows, buffaloes, bullocks, goats, sheep, pigs, hens, etc.

Question 9.
What is the important issue in Animal husbandry?
Answer:
Supplying of nutritious food, accommodating clear and hygienic shelters for animals is important issue in animal husbandry.

Question 10.
Where do people rear their cattle in the village?
Answer:
Generally villagers send their cattle to rear at the places where grass is easily available.

Question 11.
Where do farmers keep their cattle?
Answer:
Farmers keep their cattle in the sheds.

Question 12.
Name the agricultural practices done by using bullocks and he-buffaloes.
Answer:
Ploughing and levelling the field farmers use bullocks and he-buffaloes.

Question 13.
How do cattle rearers protect their cattle?
Answer:
Cattle rearers make fences in the fields at off crop seasons.

Question 14.
How is the milk production effected?
Answer:
Milk production is effected by viral and bacterial diseases.

Question 15.
In rainy season how are cattle protected from mosquitoes?
Answer:
Cattle can be protected by covering mosquito nets.

Question 16.
Who will provide treatment and health care for cattle?
Answer:
Veterinary doctor will provide treatment and health care for cattle.

Question 17.
Name the dangerous disease in cows and buffaloes.
Answer:
Galikuntu is a common and dangerous disease in cows and buffaloes.

Question 18.
From which disease sheep and goats will suffer?
Answer:
Sheep and goats will suffer from worm infections (Nattala Vyadhi)

Question 19.
How do our government treats milk production?
Answer:
Our Government treats milk production as an industry.

Question 20.
How much milk is given by traditional species of cows?
Answer:
2 to 5 litres of milk per day.

Question 21.
How much milk is given by murra species?
Answer:
Murra species give up to 8 litres of milk per day.

Question 22.
Name the traditional varieties of cows.
Answer:
Haryana, Jaferabad, Nagapuri are the traditional varieties which give good quantity of milk.

Question 23.
Name the foreign varieties of cows.
Answer:
Jersy (England) and Holstein (Denmark).

Question 24.
What is the milk yield from foreign varieties?
Answer:
They give 8 to 20 litres of milk.

Question 25.
What is pasteurization?
Answer:
The destruction of disease producing organisms present in the milk. In this process milk is heated at 62° temperature and cooled below 10°C.

Question 26.
In which months milk production is high?
Answer:
In the months of October and November milk production is high.

Question 27.
Who is the father of white revolution?
Answer:
Prof. J.K. Korian is the father of white revolution in India.

Question 28.
How is milk secreted?
Answer:
Milk is secreted from the mammary glands of animals.

Question 29.
Why do people in our country decorate their cattle during festivals?
Answer:
People believe that cattle are part and parcel of our culture. They treat them as their family members. So they decorate their cattle.

Question 30.
Why do some persons collect bones of dead animals?
Answer:
because bones are used in fertilizer industry.

Question 31.
What is the use of leather of animals?
Answer:
Leather of cattle is used in the leather industry.

Question 32.
What is Biogas? How is it produced?
Answer:
Biogas is produced from the wastes from cattle, home etc. As this is produced biologically, this gas is called biogas used for domestic purposes.

Question 33.
What are Broilers and layers?
Answer:
Broilers are the hens reared for meat and layers are the hens reared for eggs in poultry.

Question 34.
Name some local variety of poultry varieties.
Answer:
Aseel, Kadaknath, Chittagang, Longshan, Bursa are the pure local varieties.

Question 35.
What is a poultry?
Answer:
Production and rearing of hens on a large scale is called poultry.

Question 36.
In which place India is occupied in production of eggs?
Answer:
India achieved 4th position in the world by producing 41.06 million eggs per annum.

Question 37.
Name the foreign varieties of hens giving meat.
Answer:
New Hampshire, White plymouth, Rhode island red, while leg horn and Anoka.

Question 38.
What are the major practices in food production?
Answer:
Animal husbandry, poultry, fish culture, bee culture etc., are the major practices in food production.

Question 39.
In which months the egg prices are high?
Answer:
During January to April, egg prices are high.

Question 40.
Why egg prices are more in January to April?
Answer:
This is because of most of the eggs are used for hatching.

Question 41.
What is the temperature for hatchability of eggs?
Answer:
Hatchability of eggs is generally influenced by 37°C to 38°C temperature.

Question 42.
Write a slogan on nutritional Egg.
Answer:
“If you want to be healthy person eat egg every day”.

Question 43.
Name the traditional variety meant for fighting.
Answer:
Aseel (Berisa Kodi) is the Indian traditional variety meant for fighting.

Question 44.
How is hatching done in our rural areas?
Answer:
Our rural areas, the practitioner hatch eggs by placing them under broody hen.

Question 45.
What is the weight of Emu bird?
Answer:
The weight of Emu bird is nearly 50 kg.

Question 46.
What is the life span of natural wild varieties?
Answer:
Natural wild varieties grow fully in 5 to 6 years.

Question 47.
What is the life span of broilers?
Answer:
Broilers grow fully in just 6 to 8 weeks.

Question 48.
What is Apiculture?
Answer:
Culture of honey bees (apis) is called Apiculture.

Question 49.
What is the use of honey bee production?
Answer:
Development of apiculture is not only for honey production but also very much useful for crop pollination.

Question 50.
Which insects are the best pollinators?
Answer:
Honey bees are the best pollinators of many agricultural crops.

Question 51.
How much honey is produced by Indian honey bee?
Answer:
Indian honey bee produces 3 – 10 kg of honey.

Question 52.
Which honey bee is produces more honey?
Answer:
European honey bee produces 25 – 30 kgs of honey per annum.

Question 53.
Name the honey bees present in honey bee colony.
Answer:
A honey bee colony consists of one queen bee, several thousands of workers and few hundreds of drones.

Question 54.
What is the primary function of a queen bee?
Answer:
The primary function of a queen bee is to lay eggs.

Question 55.
What is the life span of a queen bee?
Answer:
The life span of queen bee is two-three years.

Question 56.
What are worker bees?
Answer:
The sterile females are called worker bees in the hive.

Question 57.
What is the function of worker bees?
Answer:
They attend to indoor duties during first three weeks of their lives such as secretion of royal jelly feeding of the brood, collecting nectar, pollen and water.

Question 58.
Name the plants that are sources of nectar.
Answer:
Fruit trees like citrus, apple, guava, tamarind, cultivated fields, crops like mustard, gingelly, wheat, cotton, sunflower.

Question 59.
What are the other products of Apiculture?
Answer:
Bee venom and bee wax are the other products of Apiculture.

Question 60.
How is bee venom used?
Answer:
Bee venom is used for the preparation of “Apistincture” used in homeopathic treatment.

Question 61.
What are the uses of bee wax?
Answer:
The uses of bee wax are production of polish cream, nail polish etc.

Question 62.
Name the parts present in a artificial bee hive.
Answer:
It consists of floor board, brood chamber, super chamber, top cover, inner cover, frames and entrance rod.

Question 63.
Name the pests and predators that attack honey bee colonies.
Answer:
Wax moths, wasps, rubber flies, dragon flies attack honey colonies. King crow, Bee eater are more harmful.

Question 64.
How are fish important for us?
Answer:
Fish constitute an important and rich sources of high quality animal protein.

Question 65.
What are the inland water areas?
Answer:
Rivers, fresh water and brackish water lakes, reservoirs, tanks, ponds, swamps etc., are the inland water areas.

Question 66.
Name the crustacean fishery.
Answer:
Prawns, lobsters and crabs together constitute the crustacean fishery.

Question 67.
Name the local varieties offish.
Answer:
Murrel (Korramenu), Katla (jalla), Katrana (bochalu), rohu (mosu), seer (vanjram) are the local varieties.

Question 68.
Name the marine fish varieties.
Answer:
Macerel, tuna, saradines are the marine fish varieties.

Question 69.
What are mechanized fishing?
Answer:
Fishermen catch fish by using machines is called mechanized fishing.

Question 70.
Name some marine fishes which are of high economic value.
Answer:
Mullets, Bhetki and peral spots, shel fishes such as prawns mussels and oysters as well as sea weed.

Question 71.
What are estuaries?
Answer:
Brackish water resources where sea water and fresh water mix together are called estuaries.

Question 72.
What is the reason for growing fish in paddy fields?
Answer:
The reason for this is increasing use of inorganic fertilizers and insecticides in paddy fields.

8th Class Biology 9th Lesson Production and Management of Food From Animals 2 Marks Important Questions and Answers

Question 1.
How do you appreciate the role of poultry to meet the food needs of the present day increasing population ?
Answer:

1. The world is facing the problem of over growth in population.
2. To meet the increasing population food needs, poultry is the best suitable option.
3. So billion hens are reared world wide for eggs and chicken.
4. India achieved 4th position in the world by producing 41.06 million eggs per annum.
5. India is placed in 5th position in the production of 1000 million kgs of chicken per year.
6. Hence, I appreciate the poultry, in fulfilling the food needs of the society.

Question 2.
“Fish has high nutrition values” said Shravya. Do you support Shravya? Why?
Answer:

1. The meat of fish contains 15-25% of proteins. Hence they are the rich sources of proteins.
2. The meat of fish has vitamins like A and D.
3. Fishes are the sources for very important fatty acids and unsaturated fatty acids which are very vital in our body’s metabolic activities.
4. Meat of fish can be easily digested. It helps in the growth and development.

Question 3.
Name the three Indian Major fresh water crops grown in fish culture.
Answer:

1. Rohu – Labeo rohita:
2. Boche – Catla catla
3. Erramosu – Cirrhinus mrigala are the three Indian major crop fishes.

8th Class Biology 9th Lesson Production and Management of Food From Animals 4 Marks Important Questions and Answers

Question 1.
This fish is called Tuna. Collect information about availability catching and marketing of this particular fish.

Answer:
Availability:
English: Big eye Tuna
Latin: Thunnus obesus
size + weight: Average today about 40 -180 c.m. about 1, 4-130 Kg.
Biggest Angled Fish: 197, 3 kg, 236 cm, Peru, 1957 Russel Lee
Maturity: Size 105 cm, weight 25 Kg., age 3 – 4 years
Maximum: Size 230 c.m., Weight 210 Kg., Age 15 years
Catching: 21% Eastern Pacific
38% Western Pacific
22% Indian Ocean
19% Atlantic Ocean
Catching Methods: Longlining, Purse seining and pole-and-line (by-catch)
Share of all Tuna: 2011 about 10% – 398.000 m.t
Main Production: Thailand, Philippines, Indonesia, Mexico, Venezuela, Ecuador, Colombia, Spain, Italy.
Life cyle: About 7-8
Major Markets: Japan (Sashimi)
Populr Product: Fresh (Whole fish)
Forms: Fresh Fillets (Sashimi)

Question 2.
Write a note on different methods used to store the fish in your area.
Answer:

1. The fish caught should be preserved in chilled conditions.
2. After catching the fish, gut is removed. Before transportation, fishes are thoroughly washed in clean and chlorinated waters.
3. They are perceived in insulated ice boxes with alternate layers of crushed ice and fishes in 1 : 1 proportion.
4. Preservation can also be done by
   a) Drying b) Salting c) Smoking d) Canning methods
5. Before canning, harmful bacteria like clostridum botulinum must be destroyed.
6. Cold storage facility and vans with refrigerated chamber have improved the storage and transport of fish.

Question 3.
Visit a poultry farm of your village. Collect the diseases of poultry and their preventive control measures. Prepare them in theform of a table.
Answer:

Diseases in Poultry birds	Casual organism	Precautionary control measures
Fowl cholera	Bacteria	Vaccination for fowl cholera is must.
Salmonellasis	Bacteria	Antibiotics with sulphur and vaccines.
Coryza	Bacteria	Sulfa drugs and antibiotics are necessary.
Fowl fox	Virus	They should be separated from the farm.
Ranikhet	Virus	Fowls should be separated from the farm and treatment should be given separately.

Question 4.
Write some diseases of tamed animals.
Answer:

1. Galikuntu is a common and dangerous diseases occur in cows and buffaloes.
2. Sheep and goats suffer from worm infections (Nattala vyadhi).
3. Some parasitic diseases cause damage to liver and intestine of tamed animals.
4. Viral and bacterial diseases also effect on milk production of cows and buffaloes.
   These are some examples for diseases in domestic animals.

8th Class Biology 9th Lesson Production and Management of Food From Animals Important Questions and Answers

Question 1.
How are the microorganisms like bacteria killed and how can the milk be preserved at milk chilling centres?
Answer:

1. Pasteurization of milk ensures the destruction of disease producing organisms present in milk.
2. In this process, milk is heated at 72°C for 30 minutes.
3. Prior to this, the milk was being cooled to below 10°C.
4. This process was invented by Louis Pasteur.

Question 2.
Dung is used as biofuel. You know that it is an accessory product. Write about such accessory products produced in animal husbandry.
Answer:
1. The supplimentary products produced from animal husbandry are meat, dung, leather, bones, horns, etc,
2. Animal husbandry is also contributing to different industries like

1. Dairy industry: Milk and milk products are produced.
2. Slaughter houses: Production of meat.
3. Leather industry: Tanning of leather and making shoes, belts and suitcases, etc.
4. Fertilizer industry : Bones of cattle are used in the production of chemical fertilizers.
5. Bio gas industry: Cattle dung is used in the production of biogas.
6. Toys industry: The horns of cattle are used to make toys and ornamental items.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 6 Sound Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 6th Lesson Sound

8th Class Physical Science 6th Lesson Sound Textbook Questions and Answers

Improve Your Learning

Question 1.
Fill in the blanks with suitable words.
a) The to and fro motion of a body from its mean position is called ……… .
b) Number of vibrations per second is called ………. .
c) The intensity of sound can be measured in ……… .
d) Sound cannot travel in ………. .
e) Vibrating bodies produce ………. .
f) The maximum displacement of a body from its mean position is called ……… .
Answer:
a) vibration
b) frequency
c) Decibel
d) vacuum
e) sound
f) amplitude

Question 2.
A normal human being can listen to sounds with frequency from …….. to ……. vibrations per sec.
Answer:
20, 20000

Question 3.
How will you differentiate the amplitude and frequency of different sounds? Give two suitable examples from your daily life.
Answer:
The pitch of a sound depends upon sound whereas intensity of sound depends upon amplitude.
If we are hearing a loud sound that means it has greater amplitude.
If we are hearing a feeble sound that means it has least amplitude.
If the shrillness of sound is less then the frequency of the sound is less.
If the shrillness of sound is more then the frequency of the sound is more.
Examples for daily life:
Frequency:

1. The shrillness of adult women is more than adult men because of greater frequency associated with vocal cords.
2. The different sounds produced by whistle and drum are due to difference in frequencies.
3. Amplitude:
   1. The difference in sound produced by lawnmower and car horn due to difference in their amplitude.
   2. The sound produced by crackers during Diwali is due to greater amplitude.

Question 4.
Write any three musical instruments that you know and explain how they produce sound? (OR)
Write any four musical instruments known to you and explain how do they produce sound.
Answer:
The three musical instruments are:

1. Veena: This instrument contain strings of different thickness fixed on hollow wooden boards, with different tensions. When a string of certain thickness fixed under certain tension is vibrated which changing vibrating lengths different sounds are produced.
2. Mridangam: It is in cylindrical shape and it containing membranes fixed with different tensions on the two sides. When it is vibrated by hand or by sticks at different places produce different sounds.
3. Flute: It has a cylindrical tube open at both ends. It is provided with holes in a row on its surface. By blowing air through it, while changing the length of air column, different sounds are produced.

Question 5.
The sounds of crickets (insects) make us close our ears. Why?
Answer:
The sounds of crickets are shrill creaking which make us to close our ears.

Question 6.
Robert observed a musical instrument producing sound. But he didn’t find any vibration of any part of that instrument. This observation raised many questions in his mind. Can you guess what are the questions raised in his mind? Write them.
(OR)
Latha observed a musical instrument producing sound. But she did not find any vibration of any part of that instrument. This observation raised many questions in her mind. Guess the questions raised in her mind and write any two of them.
Answer:

1. How does the instrument produce sound?
2. Whether an object produce sound without any vibration?
3. If it is producing vibration why do we unable to felt it?
4. Does sound has energy?

Question 7.
“Vibrations in a body produce sounds”. How do you prove it?
Answer:
Put a hack-saw blade in between a table and brick as shown in figure and press it and leave it abruptly. It produces sound and we observe hack-saw blade is vibrating. Which proves a vibrating body produces sound.

Question 8.
Can parrots speak? Discuss with your Mends and collect information.
Answer:
Yes, parrots can speak. But parrot do not have vocal cords, so sound is accomplished by expelling air across the mouth of the bifurcated trachea. Different sounds are produced by changing the depth and shape of trachea. So talking or speaking of parrots are really whistling in different variation. Parrots speak without understanding words.

Question 9.
Collect the photographs of local musicians and exhibit them in your class.
Answer:

Question 10.
Collect photographs showing various situations of sound pollution and prepare a scrap book.
Answer:

Question 11.
Zakir said “vibrations produce sound. And sound produces vibrations. This is how we hear every sound”. Establish that the given statement is true with relevant examples from your surroundings.
Answer:
Examples for vibrations produce sound :

1. Fix a rubber band tightly on an empty match box. Pluck the rubber band and keeping it near to our ear we can hear sound that shows vibrating object produce sound.
2. A vibrating hack-saw blade placed between a table and brick produces sound. Which is also an example for vibrating body produces sound.

Examples for sound produces vibration:

1. Sound produced by supersonic planes vibrates the wall of buildings and glass windows due to which we can observe the cracks on the walls or breakage of windows.
2. Take a cell phone and playing music with high volume in a plastic bottle. Close the mouth of bottle with a balloon using rubber band and place sugar crystals above the bottle. We can observe the vibrations of sugar crystals.

Question 12.
Make different musical instruments using local available materials and exhibit them in your class.
Answer:

1. Jalatarang: Take 4 to 5 metal or glass bowls or tumblers. Fill them with water in increasing order. Strike gently each bowl or tumbler with a spoon. We can produce different musical sounds. So it acts as Jalatarang.
2. Two note flute: Get a jug or bottle. Cut a smaller than finger sized hole in the bottom of the bottle / jug. Blow across the hole that is already in the top of the jug/ bottle until you get a clear note. Cover and uncover the hole on the bottom with your finger. You can also try tilting your head down and up to make the note sharp or flat.
3. Drum: Get a plastic paint barrel. Put it on the ground between your feet or in the crook of your elbow. Play it like a drum.
4. Guitar: Take empty shoe box and cut a circle in the middle. Cut six rubber bands so that they can be stretched out to their full length. Press brass fastners into the shoe box placing six on the top and six on the bottom of the box. Stretch out the rubber band, one at time, tying them onto the fastners. Cut a paper roll in half and slide in underneath the rubber bands below the hole. Which will act as guitar.

Question 13.
Explain why we are not able to hear the explosions taking place in the sun.
Answer:
Sound wave cannot travel in vacuum (meaning space). In order to hear sound waves it must required medium. So we are not able to hear explosions happening in the sun.

Question 14.
Write any two slogans to reduce sound pollution.
Answer:
Slogans to reduce sound pollution:

1. The more you make noise. The faster you lose your voice.
2. Noise an evil. You help doing it, it gives you a reward making you a deaf.

Question 15.
Write your suggestions about reducing sound pollution.
Answer:

1. Attach silencers to bikes and other machines to reduce sounds.
2. Manufacture machines that work with less noise.
3. During the use of TV and taperecorder tune down volume of sound.
4. Plant trees to reduce sound pollution.
5. Community laws must. Silence zones near school/colleges, hospitals, etc.
6. Noise producing industries, airports, bus and transport terminals and railway stations to sighted far from living places.

Question 16.
How does sound pollution effects bio – diversity? Explain.
Answer:
Slogans to reduce sound pollution:

1. The more you make noise. The faster you lose your voice.
2. Noise an evil. You help doing it, it gives you a reward making you a deaf.

Effects of sound pollution on bio-diversity:

1. The first harmful effect is loss of hearing.
2. It also leads to several health related problems, e.g: Sleeplessness, hypertension, increase in blood pressure, etc.
3. It effects the mental health of people.
4. In animals, noise can increase the risk of death by altering predator or prey detection and avoidance, interfere with reproduction and navigation and contribute to permanent hearing loss.
5. Noise pollution causes poor quality of crops.
6. Under water animals such as whales and dolphins too experience discomfort due to noise pollution caused by submarines, shipping companies and sonars. Cuttle fish and octopus suffer serious damage from noise pollution.

8th Class Physical Science 6th Lesson Sound InText Questions and Answers

Think and Discuss

8th Class Physical Science Textbook Page No. 86

Question 1.
What is the effect of humidity on quality of sound propagation? Is there any difference in propagation of sound in air during the summer and winter seasons? Discuss with your Mends.
Answer:
With increase in humidity, density of air decreases. So with rise in humidity velocity of sound increases.
This is why sound travels in humid air (rainy season or winter) than in dry air (summer) at the same temperature.

8th Class Physical Science Textbook Page No. 87

Question 2.
“Vibrations produce sound and sound produces vibrations”. Which is true in this? Discuss.
Answer:
Yes, it is true. We already know a vibrating object produce sound. Sound is a mechanical wave that can produce vibration. (Mechanical waves have ability to vibrate an object)

Question 3.
“Our ear has the three media through which sound propagates.” Discuss with your Mends as to whether the above statement is true.
Answer:
Yes, it propagates through three media. The first media is external ear, the second media is middle ear, the last media is inner ear.

8th Class Physical Science 6th Lesson Sound Activities

Activity – 1

Question 1.
Listening to sound and predicting its source:
Let us sit quietly for a while and listen to sounds of objects, animals. Prepare a list of sounds that we hear and the sources from which they might have originated. Write them in the table.
Answer:

Sound heard	Source of sound
Feeble barking	Dog from some distance
Bell ringing	School bell
Music	Radio / TV
Noise	Students in a classroom
Horn	Bike / car
Whistle	A student has produced sound from his / her mouth

Activity – 2

Question 2.
Identifying different sounds:
Make a student to stand at the blackboard such that his face is turned towards the blackboard and ask other student in the class to make different sounds. The student at the board should tabulate the sounds he heard and sources of those sounds as shown in the table.

Sound heard	Way of producing sound
Gala Gala	A few stones rattling in a metal box
Eela (whistling sound)	A student has produced the sound from her/his mouth
Tapa Tapa	Someone one striking the table tab with a scale
Taka Taka	Someone thumping the ground with shoes
DabaDaba	Someone knocking at the door
Paka Paka	Someone is laughing

a) How does the student at the blackboard guess the source of sound without actually seeing the source?
Answer:
Student has identified the variations in sound by listening.

b) How do objects produce sound?
Answer:
When we vibrating the objects, they produce sound.

c) What happens when objects made of metals are hit by a hammer or fall down from a height on a concrete floor ?
Answer:
When objects made of metals are hit by hammer from a height, they produce sound.

d) How does a flute or a whistle produce sound?
Answer:
Vibration of air column produce sound in flute or whistle.

e) How would you feel if you touch a body while it is producing sound?
Answer:
My body is vibrating when I touch a body (or object) while it is producing sound.

Activity – 3

Question 3.
Vibrating body produces sound:
Take a brass bell (bell used in Pooja room or in your school).
Ring the bell and listen to the sound carefully. Now hold the bell tightly with your hand as shown in figure and ring it again.

a) Do you hear sound from the bell ?
Answer:
Yes, but slightly.

b) Is there any change in the sound produced in the two situations?
Answer:
Yes, in the second case the sound is feeble.

c) What do your hands feel when bell is ringing?
Answer:
The hand vibrates.

d) Remove your hand and ring it again. Do you hear a different sound? Why?
Answer:
Due to the vibrations are transmitted to hand and bell is not properly vibrating so it produces a feeble sound. Once the hand is removed bell rings properly and sound become louder and different.
Let us do following activities:

e) Fix a rubber band tightly on an empty matchbox. Pluck the rubber band and keep it close to your ear. Do you hear any sound? Do you feel any vibration in your hands?
Answer:
Yes, I heard a sound. I felt the vibration.

f) Blow air into papers of your notebook. What happens? Does the action produce any sound? Do you find any vibrations in the note book?
(OR)
If you blow air into papers of your notebook, sound will be produced. Write your observation in this activity.
Answer:
Yes, it produce sound and I found vibrations in the notebook.

g) Fill a plate with water and let the water settle. Strike the rim of the plate with a spoon as shown in figure. What do you observe? What do you hear? Where do you find vibrations in this case?

Answer:
I heard a sound. The vibrations are found in plate as well as in water.

h) Put a hack-saw blade in between a table and a brick as shown in the figure and press it and leave it abruptly. What happens? Does it produce sound? What is the state of the hacksaw blade while it is producing sound?

Answer:
Yes, it produces sound. The blade is vibrating.

i) What have you observed while doing the above activities?
Answer:
All of them produced sound.

j) What changes took place in those objects?
Answer:
These objects are vibrate while producing sound.
But there are certain instruments which producing sound though we cannot see any vibrations in the instruments like in flute and clarinet etc.

k) How do they produce sound?
Answer:
They are producing sound due to vibration of air column.

l) Is it possible to produces sound without vibration?
Answer:
No, it is not possible to produce sound without vibration.

m) Does every vibrating body produce sound?
Answer:
Yes, every vibrating body produce sound.

n) Does sound has energy?
Answer:
Yes, sound has energy.

Activity – 4

Question 4.
Sound has energy: (OR)
Suggest an activity to prove “sound has energy”.
Take a plastic bottle and a cell phone. Cut the top of the bottle so that it looks like a glass. Play songs on the mobile phone in high volume and place it in the bottle. Close the mouth of bottle with a balloon using rubber band so that it covers the bottle as shown in the figure and stretch it tightly so as to behave like a diaphragm. Place some sugar crystals or small size of sand particles on the balloon diaphragm and observe the movement of particles. Do the same activity after removing the phone from the bottle.

a) What do you notice?
Answer:
When there is no cell phone inside the bottle, sand particles on diaphragm remain stationary. While the cell phone playing songs inside the bottle, the diaphragm vibrates which can be seen through dancing of sand particles. The sound produced by cell phone inside the bottle is responsible for these vibrations. Thus sound has energy to make sand particles vibrate on the diaphragm.
Musical instruments:
You might have observed many musical instruments like Tabala, Flute, Harmonium and Guitar. The sounds produced by these instruments are distinct. It is easy for us to identify which sound is coming from which instrument.

b) How do they produce sound?
Answer:
They produce sound due to vibration.

c) Why there is a difference between the sounds produced by various musical instruments?
Answer:
The mode of vibration is different.

d) Which part of these instruments is responsible for production of sound?
Answer:
Different parts for different instruments:

Name of instrument	Vibrating part of it
Tabala	Membrane, air inside hollow body
Veena	String fixed on hollow wooden board
Flute	Air columns
Clarinet	Air columns
Guitar	String fixed on hollow wooden board
Mridangam	Membrane, air inside hollow body

e) Can you name the instrument for which more than one part is responsible for the production of sound?
Answer:
Tabala, Mridangam.

f) How do you compare the production of sound in a flute and sound produced in a water tap when it is turned on, just before the water flows out of it.
Answer:
Both are same process. They produce sounds due to vibrating air columns.

Activity – 5

Question 5.
Producing a sound that resembles sound of rainfall:
Start clapping with fore finger on left hand palm, add the middle finger and clap again, then ring finger and lastly small finger successively and reverse the process gradually. If all the students in your class do it simultaneously the sounds produced would resemble the on set and stopping of rainfall.

Activity – 6

Question 6.
Observing the changes in sound:
Take 4 or 5 metal glass bowls or tumblers. Fill them with water in decreasing order. Strike gently each bowl or tumbler with a spoon.

a) What do you hear?
Answer:
We can hear a musical sound. This is a jalatarang.
Fill the bowls or tumblers with equal amounts of water, strike each ball like in above case and listen the sound.

b) What difference do you notice in the sound produced?
Answer:
It does not produce musical note in this case.

c) Why is there variation in the sound produced due to change in the water level of a bowl?
Answer:
The change is due to change in air columns. That is sounds are produced by the vibrating bodies and air passes through orifices of the instrument.

Activity – 7

Question 7.
Observing the movements of vocal cords during speech :
Ask a friend to raise his neck up. Stretch a chocolate wrapper across his mouth and ask him to blow air on the wrapper forcibly. Observe the changes in movement at his throat. Ask him to blow again slowly and observe the difference in movements.
a) What changes do you observe in the movements at the throat on the two occasions?
Answer:
During the first trial the voice box gets tensed and produces high sound while during the second trial it is close to normal position of throat and produces lower sound. The sound produced in the above activity is due to a combination of vibrations produced in the wrapper and the vocal cord.
Propagation of sound:
Sound needs a medium to propagate:
The sound produced by the school bell will be heard by all of us irrespective of whether we are in a room opposite to the bell or in a room at the back of the bell. Obviously, the sound produced by the school bell travels in all directions and reaches us, propagating through the air present between source of the sound and our ears. That is the air surrounding us act as a medium which allows the sound to pass through it.

b) Does sound travel only in air?
Answer:
No, it will travel in other media.

c) Does it travel in any other gaseous medium?
Answer:
Yes, it will travel in any other gaseous medium.

d) Does sound also travel in other media like solids and liquids?
Answer:
Yes, it will travel.

Activity – 8

Question 8.
Observing sound propagation in solids:
Strike one end of the table with a pen and ask your friend to listen to the sound produced keeping her ear touching the table at other end and also ask her to listen to the sound by lifting her head slightly from the table. Ask your friend what difference she noticed while hearing the sounds when her ears were away from the table and touching the table.

Take a metal or wooden strip. Strike it at one end and ask your friend to hear the sound by keeping his ears at the other end of the strip. Ask your friend what difference he noticed while hearing the sounds when his ears are away from the strip and touching the strip.

a) Do you know how to make a toy telephone using tea cups?
Answer:
Take two paper-cups. Make small holes at the bottom of these cups. The holes should be very small so that only a thin string can pass through them. Take a long string. Make sure that the string does not have any knots in it. Push the string through the hole in one of the cups. Fix the string by putting a knot at the end. Similarly fix the string to the other cup. Our phone is ready.

You and your friend can communicate with this phone now. Stand away from each other so that the string is tightly held. One of you can speak in the cup while the other can listen by putting the cup on his ear.

b) Are you able to hear the sound?
Answer:
Yes, we can hear the sound.

c) What is a medium between you and your Mend which is responsible for propagation of sound?
Answer:
The medium is thread.
In the above activities you observed that sound travels in solid medium like wood, metal, thread, etc.

Activity – 9

Question 9.
Propagation of sound through liquids:
Take a bucket fill it with water. Take two stones and strike them against each other keeping your hands inside the water. Ask your friend to listen to the sound by keeping his / her ears touching walls of the bucket.

Ask your friend about the difference between sounds produced by striking the stones against each other in water and striking them in air.
Thus the conclusion is that sound propagates through matter in all the three states – solid, liquid and gas.
a) Does sound travel in liquids?
Answer:
Yes, sound can travel in liquids.

b) Can we hear the sound produced in water?
Answer:
Yes, we can hear.

Activity – 10

Question 10.
Does the sound travel if there is no medium?
Take a water tumbler or a glass made of plastic or glass. Make sure that the tumbler or the glass is dry. It should be long enough to accommodate a cell phone vertically. Place a cell phone small in size in the glass and play the ring tone of the mobile. Listen to the ringtone and its volume level. Cover the glass with a small plate and again listen to the ringtone and note the difference in volume of the sound.

Now suck the air from the glass keeping it close to your mouth. If you suck air quickly the rim of the glass will stick around your mouth due to air lock. Listen to the volume of the ringtone at this stage. And also ask your friend to listen to the sound for comparing variation in its volume.
a) Is there any change in the volume of sound observed by you or your Mend?
Answer:
When the tumbler is covered with a plate, the volume reduces but you can hear the ringtone. As we start sucking more and more we can notice that the volume decreases gradually. If the air is sucked completely, you will not hear the sound at all. But practically it is not so easy.
This activity gives an idea about need of a medium for propagation of sound.

Lab Activity – 1

Question 11.
Conduct an experiment to know the relationship between the intensity of sound produced by a body and the vibration of the body.
Answer:
Aim: To know the relation between the intensity of sound produced by a body and the vibrations of the body.
Materials required: Wooden table, 30 cm metal scale or nearly 30 cm hack-saw blade and a brick.
Procedure:
Place the blade/scale on the table, with 10cm of the blade on the surface of the table and rest of it in air. Keep a heavy brick on one end of the 10 cm blade/ scale kept on table.

Vibrate the blade gently and observe the vibrations and simultaneously listen to the sounds. Repeat the same 2-3 times and record observations in the table shown below.
Vibrate the blade using greater force. Observe the vibrations and listen to the sound. Repeat this for 2-3 times and record your observations in the table shown below.

Force	Vibrations of the. blade / scale	Intensity of sound
Small	50	Less
Large	50	More

a) When do you hear a loud sound?
Answer:
When we applied large force we heard a loud sound.

b) When do you hear a feeble sound?
Answer:
When we applied less force we heard a feeble sound.

c) What difference do you notice in vibrations of blade / scale during loud and feeble sounds?
Answer:
During loud sound the amplitude of vibration is more and for feeble sound the amplitude is less.

d) What difference do you find in amplitude of vibration for a feeble and a loud sound in the above experiment?
Answer:
For a loud sound the amplitude is more and for a feeble sound the amplitude is less.

Lab Activity – 2

Question 12.
Explain identification of pitch or shrillness of sound with the help of an activity.
(OR)
What are the characteristics of sound? Explain the procedure to identity the pitch of sound.
Answer:
Chardcteristics sound are 1) Loudness 2) Pitch 3) Quality.
Aim: Identifying pitch or shrillness of a sound.
Materials required: A wooden table, two hack-saw blades or metal scales of 30cm length and a brick.
Procedure:
Place the first blade/scale on the table, with 10cm portion of the blade on the table and rest of it in air. Keep a brick as weight on the 10 cm portion of the blade/scale kept on the table. Vibrations of hack-saw blades
Place the second blade/scale on the table (see that the gap between these two blades is 10cm), with 25cm on the table and 5cm in air. Keep a brick as weight on the scale/blade.

Vibrate both blades with same force. Observe the vibrations and listen to the sounds produced.
Repeat the same 2-3 times and record observations in the table showed below.

Blade length in air	Vibrations	Sound
Blade 1 : 20cm	50	Less shrillness
Blade 2 : 5cm	90	More shrillness

a) What difference do you notice in number of vibrations of two blades?
Answer: The number of vibrations in 5 cm blade is more.

b) What difference do you notice in the quality of sound produced by them?
Answer:
The sound produced by 5 cm blade is more shrill when compared to that of 20 cm blade.

 

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 12 Stars and the Solar System Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 12th Lesson Stars and the Solar System

8th Class Physical Science 12th Lesson Stars and the Solar System Textbook Questions and Answers

Improve Your Learning

Question 1.
What is your local noon time?
Answer:
The time when the shortest shadow of a vertical object occurs in a particular place is called local noon time at that place.

Question 2.
Where do you find moon at night?
a) 2 days before Poumami
b) 2 days after Amavasya
Answer:
a) Couple of days (2 days) before full moon day (Pournami), a crescent is seen in the west just after sunset.
b) Couple of days (2 days) after the new moon day (Amavasya), a crescent is seen in the west just after sunset.

Question 3.
Why doesn’t eclipse occur on every full moon day or on every new moon day?
Answer:
Lunar eclipse can happen during a full moon and only when the moon and earth and sun are directly in line and the moon passes through the earth shadow. Most of the time the moon is slightly out of line and that is why we don’t have a Lunar eclipse every full moon.

Question 4.
Where do you find the pole star?
Answer:
The pole star lies on the line joining the two outer stars of the constellation great bear. Pole star directly above the north pole of earth.

Question 5.
What Is the difference that you find between pole star and other stars?
Answer:
If we observe the position of various stars constantly. We will notice that they are not in a fixed position because as the earth rotates about a fixed axis, the position of stars with respect to earth changes. But the position of pole star does not change with respect to earth.

Question 6.
Why does polestar seem to be stationary?
Answer:
The polestar is situated in the direction of the earth’s axis and that is why it does not appear to move even though all stars appear that they are moving because of ie rotation of earth. So pole star seems to be stationary.

Question 7.
Name some constellations.
Answer:
Names of some constellations:

1. Great bear (Saptarishi)
2. Cassiopeia (Sharmistha)
3. Orion
4. Leo (Simha)
5. Corona
6. Borealis

Question 8.
How many planets are there in our solar system? What are they?
Answer:
There are 8 planets in our solar system. They are:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus and
8. Neptune.

Question 9.
Look at the below table and name the smallest and the biggest planets in our solar system.

Answer:
From the table the biggest planet is Jupiter and the smallest planet is Mercury.

Question 10.
Among all 8 planets what is the special thing about earth?
Answer:
The special thing about earth is it is the only planet in the solar system on which life is exist.

Question 11.
How do day and night occur?
Answer:
The day and night occur due to rotatory motion of earth.

Question 12.
Do the stars appear moving? How can you say?
Answer:
Yes, stars are appear moving. Our galaxy like all other spiral galaxies is rotating. The stars move on orbits around the centre of the galaxy. It was the motions of stars in external galaxies that lead to the idea of dark matter in the universe. Stars also have some random motions. They do not orbit galaxy in exact circles. As observers we see this motion of the stars as what is called proper motion, the projection of their velocity on to the plane of the sky is radial motion.
Normal Answer : Alternate answer is No. All the stars appears that they are moving because of rotation of earth.

Question 13.
Is it possible to see the polestar for the people who live in the southern hemisphere of the earth? Why?
Answer:
A pole star is a visible, preferably a prominent one, that is approximately aligned with the earth’s axis of rotation. The term polestar refers to polaris which is the current northern pole star also known as the north star. So the people in southern hemisphere unable to see this pole star.

Question 14.
What is the use of artificial satellites in our daily life?
Answer:
Artificial satellites have many uses in daily life.

1. They are used for forecasting weather.
2. They are used for transmitting television and. radio signals.
3. They are also used for telecommunication.
4. They are used in aviation and military (these satellites are called remote sensing which will collect information from a distance).

Question 15.
Why is Venus the brightest planet?
Answer:
Venus is very bright that’s partly because sunlight easily reflected by acidic clouds that blanket the planet atmosphere and also it is closest planet to earth.

Question 16.
Are you curious about going to the moon? Why?
Answer:
Yes, I am curious about going to moon. Because I want to find answers raised in my mind.

1. Is it true there is no life on moon?
2. If it does not have atmosphere, how it look like?
3. How earth look like from moon?
4. Whether there are any mountains on moon or not?
5. There may be any creators on moon or not?
6. Whether there is any form of water exists on moon?
7. Whether we able to walk on moon as freely as on earth surface?

Question 17.
While observing the shadow of a stick from morning to evening, some questions arose in Ramya’s mind. What may be those questions?
Answer:

1. Why sun is changing its position from morning to evening?
2. How does the length of the shadow change with time?
3. Why we are getting longest shadows in the morning and evening?
4. Why the shadow in the noon is shortest?
5. Do all the days at noon have same size of shadow?

Question 18.
What are the questions that engage your mind when you look at night sky?
Answer:

1. Is stars collide with each other?
2. Where does the stars go in the morning?
3. Whether stars daily travel in the same path?
4. Why night sky is black and early morning sky is blue?
5. Whether we can count stars in the sky?
6. Why stars grouped to form constellations?

Question 19.
Even though we do not have clock, we can know the time by observing some shadows in daytime. Think and discuss with your friends how we can know the time at night?
Answer:
We can know the time by position of moon and stars or with reference to pole star. Estimation of time by using position of moon:

1. If the moon is full do the experiment stop if it is new moon.
2. Imagine the moon is divided into 12 vertical strips. First hour at right edge and last hour at left edge. It can vary by season or location.
3. Read the moon from left to right following an imaginary horizontal half line.
   Look for where the line intersects the boarder between light and dark. Make a note of which strip that intersection is in.

For example:
The instruction is at 8 pm and transition from right to left is from light to dark. This tells us the moon will set in the west at 8 pm.
This moon will set at about 7-8 hours after sunset. If sunset is at 8 pm. You can expect moon time is at 3-4 am.

Question 20.
How can you find north – south direction at your place?
Answer:
This experiment should be performed on a day when the sky is clear, preferably between nine in the morning and four in the evening.

Pick a spot in open ground away from buildings and trees. The spot should be as flat as possible.
Take a stick which is a little over a meter long and fix it vertically in the ground. Ensure that exactly one meter of stick remains above the surface of ground. Build a fence around your stick as shown in figure.
Make your first observation at nine in the morning, Make a mark with a nail or peg at the point where the tip of the shadow falls on ground. Measure the length of the shadow.
Then, make similar observations for every half an hour throughout the day till four in the evening.
Find the direction of shortest shadow cast by vertical object on the ground. That gives the north-south direction.

Question 21.
In which direction (towards north or south) is the sun moving day by day when you read this lesson?
Answer:
From December 21 to till June 21 the sun appears to shift northward. From June 21 to December 21 the sun appears to shift southward.
(Basing on this information we have to give the answer suppose you have read the lesson in the month of February the sun is moving towards north direction).

Question 22.
What are the planets you have seen in the sky? When do you observe those planets?
Answer:
The two planets observe in the sky are

1. Venus: Sometimes Venus appears in the eastern sky before sunrise. Sometimes it appears in the western sky just after sunset. Therefore it is often called a morning or an evening star.
2. Mars: It appears slightly reddish and therefore, it is also called red planet. It appears in the east.

Question 23.
What is the duration of a day and night today? Collect the information about duration of day and night for the past 7 days from the newspapers, analyze it and say whether summer or winter is going to come.
Answer:
Students have to collect the information from newspaper and other resources.
(Hint: If sun is shifting towards south the upcoming season is winter if it is shifting towards north the upcoming season is summer).

Question 24.
What are the other districts on the same latitude as your district ?
Answer:
I am residing at Krishna district. The latitudes of Krishna district are 16. The other districts which have same latitude are West Godavari, Mahaboobnagar.
(You should write the latitude of your district and you have to find out the districts which lie in that latitude from table -1 on page 163 of textbook.)

Question 25.
Collect the information about cosmic dust (wastage) from newspapers, internet and make a poster on your school panel board about the consequences of cosmic dust.
Answer:
Cosmic dust: Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 mm in size.
Consequence of cosmic dust:
The orbit of space junk could deteriate resulting in the junk falling to earth. If it survives and reaches the earth’s surface it would cause the same damage as equally sized meteorite, including damaging or destroying structures in the area killing people, etc.
The earth receives hundreds of tonnes of space dust, rocks, etc every week. If you were to get whole load of it in one place and try and breathe it in it probably would be harmful. However natural concentrations are so low that it possess no risk.

Question 26.
Make a sundial. Explain how you made it.
Answer:
Making of sundial:
Cut a right angled triangle ABC from a sheet of cardboard. Angle C of the triangle should equal to the latitude of your city or town and angle A should be 90° as shown in figure.

Fix cardboard triangle vertically in the middle of a rectangular wooden board. Glue strips of paper along both edges of BC and the wooden board to make the triangle stand erect.
Place your board with the triangle on level ground in an open space which gets sunlight throughout the day. Base BC of the triangle should be placed in the north- south direction, with B pointing to the north.
At nine in the morning, draw a line along the shadow of side AC on the wooden board. Write the time along side of the line. Draw lines of the shadow of side AC at one hour intervals through the day till sunset and mark the time for each line. The sundial is now ready.

Question 27.
Draw the different phases of moon. Arrange them in an order from poumami to amavasya.
Answer:

Question 28.
Draw the location of polestar showing the direction from Great Bear.
Answer:

Question 29.
Draw the diagram of the solar system.
Answer:

Question 30.
How do you appreciate the construction of knowledge about the universe by our ancestors?
Answer:
They study of our universe changed from time to time from earth is flat to higgs bosan particles. All these secrets about our universe are revealed due to constant afforts of our ancestors. That is due to construction of knowledge about the universe by our ancestors. So the afforts of our ancestors should be thoroughly appreciated.

Question 31.
We launched so many artificial satellites around our earth for different purposes. What do you think about the impact of artificial satellites and their radiation on bio-diversity?
Answer:
Effect of radiation released from artificial satellites on biodiversity:
I. Animals and humans:

1. Killing certain enzymes in the body can simply make sick.
2. If radiation damages DNA, the body may not repair it. It increases the chances of both animals and humans developing cancer.

II. Marine animals: High level of radiation cause a reduction and reproduction capabilities of marine animals.
III. Plants: Weaking of seeds and frequent mutations. Excess of radiation killing plants.

Question 32.
Among eight planets of our solar system, earth is the only planet supporting life. Explain how we should protect our earth and its environment.
Answer:
Steps to be taken to protect earth and environment:

1. Reduce pollution by reducing air, water and land pollution.
2. Recycle resources by sending the degradable like paper and non degradable like plastic and glass objects to recycling factory.
3. Save resources by using them carefully. E.g.: Water, trees, wood, paper.
4. Stop burning fossil fuels (Coal, oil and natural gas) for that do not waste electricity.
5. Plant lot of trees.

8th Class Physical Science 12th Lesson Stars and the Solar System InText Questions and Answers

8th Class Physical Science Textbook Page No. 160

Question 1.
What are the celestial objects that we can see in the sky?
Answer:
Stars, Planets, Moon (Satellite), Comets, Meteors and Meteorites are the celestial objects that we can see in the sky.

Question 2.
Are the stars moving?
Answer:
Yes, the stars are moving.

Question 3.
Do you see the same stars at night and early in the morning?
Answer:
No, we do not see the same stars at night and early in the morning.

Question 4.
Do you see the same stars during summer and winter nights?
Answer:
Yes, it is due to the change of axis of rotation of the earth.

Question 5.
What is the shape of the moon? Why does it change? Why doesn’t the sun change its shape daily like the moon?
Answer:
The actual shape of the moon is approximately spherical.
But it changes everyday.
The sun does not change its shape like the moon due to its size and the distance it is away from the earth. Moreover the shadow of the earth falls on one side of the moon partially or fully. This makes the changes in its shape. Also the moon does not have its own light to make the shadow of the earth to fall on the huge sun.

Question 6.
Where exactly is the sun situated in the sky at noon?
Answer:
Above our head (vertically above) (Really the sun does not revolve around the earth but due to the rotation and revolution of the earth we feel / imagine that the sun moves around the earth.)

Question 7.
Why does the shadow of a tree change from morning to evening?
Answer:
Due to the rotation of the earth we find the sun at different positions in the sky which brings the tree the different shadows from morning to evening.

8th Class Physical Science Textbook Page No. 168

Question 8.
Will we be able to hear any sound if we were on the moon? Why?
Answer:
Sound required a medium for its propagation. There is no atmosphere (medium) on moon. We know sound cannot travel in vacuum. So we unable to hear any sound if we were on the moon.

Question 9.
Can any life exists on the moon? Why?
Answer:
Moon does not have air (oxygen) and water which are essential for existence of life. So there is no life exists on moon.

8th Class Physical Science Textbook Page No. 169

Question 10.
Why does lunar eclipse occur only on a full moon day?
Answer:
Lunar eclipse occur only on a full moon day because lunar eclipse happen when the earth’s shadow falls on the moon, hiding it from the sun’s light. For this to happen, the moon must be on the opposite side of the earth from the sun. So the full half of the moon that is lit by the sun is visible from earth that is full moon day.

Think and Discuss

8th Class Physical Science Textbook Page No. 161

Question 1.
Look at the nails or pegs you have fixed on the ground to keep track of the shadow of the stick throughout the day. From their positions, can you tell how the position of the sun changes in the sky from sunrise to sunset?
Answer:
The position of sun changes from slanting to vertical and then vertical to slanting.

8th Class Physical Science Textbook Page No. 163

Question 2.
Why does the sun appears to travel towards north or south? Try to find the answer by reading your social studies chapter “Earth movements anti seasons” along with this lesson.
Answer:
The earth’s tilt is constant 23.5 degree perpendicular. The earth position relative to sun changes, not the tilt itself during orbit. The sun is moving towards north throughout summer because the north pole is tilted 23.5 degree towards sun and we are in northern hemisphere. During the winter the south pole is tilted 23.5 degree so the sun appear to travel towards south.

8th Class Physical Science Textbook Page No. 168

Question 3.
Scientists are planning to build settlements on moon and are trying to make arrangements to live there. You know that there is no air on moon. How will it be possible to live on the moon then?
Answer:
Oxygen is essential for humans. Unless we built special structures and buildings on the moon and put oxygen into them, we would not able to live on the moon without wearing oxygen tanks all the time.

8th Class Physical Science Textbook Page No. 178

Question 4.
The diameter of the sun is 13,92,000 Km. The diameter of the earth is 12,756 Km. The diameter of the moon is 3,474 Km. The distance from the sun to earth is 15,00,00,000 Km. The distance from the earth to moon is 3,84,399 Km.
Take the scale as 1 lakh km = 1 cm, and imagine how the arrangement of sun, earth and moon is in our universe. Can you make this arrangement on your school ground?
Answer:
Yes, we can do it in our play ground. Placing sun at the middle. Rotating earth around sun and rotating moon around earth by measuring diameters in cm.

8th Class Physical Science 12th Lesson Stars and the Solar System Activities

Activity – 1

Question 1.
Observing the changes in the length of shadow.
This experiment should be performed on a day when the sky is clear, preferably between nine in the morning and four in the evening.

Pick a spot in the open ground away from trees and buildings.
The spot should be as flat as possible. Take a stick which is a little over a meter long and fix it vertically in the ground. Ensure that exactly one meter of stick remains above the surface of ground.
Make your first observation at nine in the morning. Make a mark with a nail or peg at the point where the tip of the shadow falls on ground. Measure the length of the shadow.
Then, make similar observations for every half an hour throughout the day till four in the evening.
Use a clock to fix the time for making your observations. Enter the measurements of the length of the shadow and the time of measurement in a table making two columns, one for time and another for length of shadow.

Time	Length of the shadow
9.00 am	1.75 m
9.30 am	1.7 m
10.00 am	1.6 m
10.30 am	1.5 m
11.00 am	1.1 m
11.30 am	0.8 m
12.00 noon	0.7 m
12.30 pm	0.81 m
1 pm	1.12 m
1.30 pm	1.3 m
2.00 pm	1.5 m
2.30 pm	1.75 m
3.00 pm	1.84 m
3.30 pm	2.2 m
4.00 pm	2.5 m

(These values are changes from place to place and with seasons)
a) Look at your table and figure out the time of the day of shortest shadow.
Answer:
I observed at 12 noon.

b) When did you observe the longest shadow in your activity?
Answer:
At 4 pm.

c) How does the length of the shadow change with time? Illustrate your answer with the help of some diagrams. Draw the diagrams of the stick and its shadow for 5 different times, that is, at 9am, 1 lam, 12noon, 2pm and 4pm.
Answer:
The size of the shadow decreases and reach a minimum and then increases (It has minimum value at 12 noon)
(Students have to draw the diagrams of the stick and its shadow at 9 am, 11 am, 12 noon, 2 pm and 4 pm by doing this activity)

d) If you continue your activity from sunrise to sunset, at what times do you think the shadow would be the longest?
Answer:
At sunrise and at sunset.

e) Where is the sun situated in the sky at noon? Where does the shadow of stick is fall at that time? Think about how your own shadow will be at that time.
Answer:
Almost in line with the stick. It will falls in north-south direction. My own shadow is also in north-south direction.

f) Do you think that your shadow length will be the same on all the days at noon?
Answer:
Yes, the shadow will be same on all the days (with in two weeks).

g) In which direction does the shortest shadow of the stick fall in your activity?
Answer:
The shortest shadow falls in the north-south direction.
Continue your observations.

h) Observe on the next day whether the shadow of the stick falls at the same spots at the same times throughout the day.
Answer:
Yes, it falls on the same spot.

i) Can you use your stick as a clock (sundial) to tell the time? If your answer is ‘yes’, explain how this is possible.
Answer:
Yes, due to movement of sun from east to west.

j) Two weeks later, once again check to see whether the stick’s shadow falls at the same spots at the same times during the day.
Answer:
It fall on the same spot. But length of shadow change.

k) If the shadow does not fall on the same spot, what could be the possible reason?
Answer:
The position of the sun in the sky changes during the day.

l) If you continue the experiment the position of shadow changes or not ?
Answer:
No, it does not change. The position of sun changes from day to day as well.
That is, the position of the sun at 10.00 am today will be different from its position two weeks later at the same time. If you choose a particular time every week and mark the position of the sun with a peg at that time, you can build a calendar for the full year.

m) During a period of two weeks you had made an observation that the length of the shadow at a particular time is changing day by day. Did it become longer or shorter?
Answer:
Yes, it is changing day by day. During summer it is shorter day by day and during winter it is larger day by day.

n) By observing the direction of shadows, can you guess the arrival of summer or winter?
Answer:
Yes.

Activity – 2

Question 2.
Understanding the north-south movement of the sun.
Fix a spot near your home from where you can observe the sunrise. You may have to go to the terrace of a RCC building or go to an open field for the purpose. Choose a tree or an electric pole or some other stationary object as a reference point.

Over the next 10 to 15 days, note the spot at which the sun rises daily, keeping in mind your reference point. Make a daily sketch of the rising sun as well as your reference point in your notebook during this period.
a) Does the spot of sunrise change? If it does, in which direction does it seem to move?
Answer:
It may moves towards south of the sky if it is Dakshinayanam or it may moves towards north of the sky if it is Uttarayanam.
(So answer based upon Uttarayanam or Dakshinayanam)

b) Was the sun appear travelling towards south or north during the time you made your observations?
Answer:
It is travelling towards north.

c) Do you think that is the reason for the change in the length of the shadow of the stick day by day in activity 1 ?
Answer:
Yes, that is the reason.

d) Assuming that you did not have any calendar and knowledge of months and seasons, can you use movement of the sun to predict the arrival of winter or summer?
Answer:
Yes, if it is moving towards north, the coming season is summer (in the above case it is summer) and if it is moving towards south, the coming season is winter.

Activity – 3

Question 3.
Make your own sundial.
Answer:
First of all, you will need to cut a right angled triangle ABC from a sheet of cardboard. Angle C of the triangle should equal to the latitude of your city or town and angle A should be 90° as shown in figure.

A list of latitudes of districts of Andhra Pradesh is given below in table.

Fix your cardboard triangle vertically in the middle of a rectangular wooden board. Glue strips of paper along both edges of BC and the wooden board to make the triangle stand erect.
Place your board with the triangle on level ground in an open space which gets sunlight throughout the day. Base BC of the triangle should be placed in the north- south direction, with B pointing to the north.
At nine in the morning, draw a line along the shadow of side AC on the wooden board. Write the time along side the line. Draw lines of the shadow of side AC at one hour intervals (use a clock to check the time) through the day till sunset and mark the time for each line. Your sun-dial is ready.

Activity – 4

Question 4.
Observing phases of the moon.
a) Have you ever observed the movement of moon in the sky?
Answer:
Yes.

b) Does the moon appear at same point at a particular time everyday?
Answer:
Yes.

c) s the shape of the moon same on everyday?
Answer:
No, it changes.

Now note the date of the day after new moon day (amavasya), when the moon first appears in the sky.
Also note the time at night when the moon sets (goes down in the western sky). In the same way everyday locate the moon in the sky at the time of sunset or immediately after sunset.
Record the date and time of the moon set and draw a picture of the moon as you see it on that day in your notebook as shown in figure.
Continue making observations for as many nights as possible.
Observe the moon a few days before full moon day (Pournami) to a few days after it. Locate the position of moon in the sky at the time of sunset before Pournami and note the time and position of moon in the sky at that time.
After Pournami, note the time at which the moon rises (comes in the eastern sky) and also note the date. Draw pictures of the shape of the moon each of these days.

d) Can you calculate the number of hours between one moon rise and the next moon rise or the number of hours between one moon setting and the next moon setting, with help of these observations?
Answer:
It is about 24 hours and 50 minutes.

e) How many hours lapse between one sunrise to the next, or one sunset to the next?
Answer:
It is about 24 hours.

f) Is the time period same for sun and moon to appear at selected position after completing a cycle in the sky every day?
Answer:
No, they are different.

g) Does the moon appear at the same point every day during the time of the sunset?
Answer:
No.

h) What is the shape of the moon? Is it same every day?
Answer:
It is changing day by day.

i) You might have observed that the shape of the moon changes night after night. What is the name given to these changes in appearance ?
Answer:
These changes in its appearance are called the phases of the moon.

j) Can you guess why the shape of the moon changes?
Answer:
The time period taken by sun to complete a cycle in the sky and come to the selected position is almost same everyday and it is about 24 hours i.e., 1 day. Whereas moon takes about 50 minutes more than a day to complete the cycle and which results in the phases of moon.

Activity – 5

Question 5.
A Moon-shaped lemon.
Answer:
Choose a day one week after the new moon day when the moon is visible in the sky during the day time.
Take a yellow lemon or a whitewashed clay ball and pivot it on a long needle or on a spoke of bicycle. Hold it up towards the moon as shown in figure.

Ensure that you are standing in the sun¬shine when you do this activity.
Observe the shape formed by the sunlight on the surface of the lemon. Is there some similarity between the shape formed and the shape of the moon?
It forms one of the phase of moon.

Activity – 6

Question 6.
Why does the shape of the moon change ?
(Do this activity around 4p.m.)
Wrap a ball tightly with a white hand-kerchief or with a piece of white cloth.
Assume this is the moon. Hold this ball in front of your eyes in bright sunshine as shown in figure and turn around yourself slowly. Observe how the shape of the illuminated part of the ball changes.

a) Does sunlight fall on half the ball at all times while you turn around?
Answer:
Yes.

b) Is the shape of the illuminated part on the ball viewed by you same in all positions during your rotation?
Answer:
No, they are different.

c) Why does this happen?
Answer:
To understand this look at figure.

c) Why does this happen?
Answer:
To understand this look at figure.

The large circle in the middle of figure is the earth and the smaller circles around it represent the moon in different positions. We can see the phases of the moon on different days in the figure. The sunrays falling on the moon illuminate half its surface in all the positions. However, we cannot see the entire illuminated surface in all the positions. In some cases we see the entire illuminated surface while in others we see only part of it. In one particular position, we cannot see the illuminated surface at all.
The shape of the moon we see is the shape of the illuminated portion visible to us.
In figure, the day of the new moon is called day 0 or day 28 (position 1). In this position, the illuminated surface is not visible from earth, so the moon cannot be seen from earth.
Four days later, when the moon is in position 2, a small part of its illuminated surface is not visible from earth. On day-7, the moon is in position 3, so more of its illuminated part is visible from earth.
After fourteen days (at position 5) the entire illuminated surface of the moon is visible from earth. This is the day of the full moon.
Subsequently, the moon appears smaller with each day as it passes through positions 6 (day-18), 7(day-21) and 8(day- 25). After 28 days, the moon is once again in position 1.
Try to duplicate position 1 with the ball. For this, you will have to hold the ball towards the sun (between your eyesight and the sun).

d) In this position, which half of the ball is illuminated?
Answer: Although half the surface of the moon is illuminated everyday, we cannot see the moon on new moon day since the illuminated surface is on the side opposite to the point of observation on the earth. On a full moon day, the situation is reversed. The illuminated half of the moon faces the point of observation, so we see a full moon.

e) Where is the position of sun and moon on new moon day and full moon day?
Answer:
The sun and moon must be on the same side of the earth on a new moon day and they are on opposite sides of the earth on a full moon day.

f) Can you now state as to in which direction the moon will rise on a full moon day?
Answer:
The moon will rise from west on full moon day.
While we observe moon in clear sky on a full moon day, we think about the spots those are visible on the moon. In olden days people are curious about the spots. This led to creation of a lot of stories.

e) Do you know any such story?
Answer:
One popular story to account for the dark spot on the moon is that Ganesha, once filled with food, fell from his mouse and broke his stomache. Chandra laughed at this, at which Ganesha injured him by breaking off and throughing one of his tusks and cursed him.

Activity – 7

Question 7.
Observing the movement of constellations (stars).
Take a 20cm x 20cm square sheet of paper and make a 1cm diameter hole in its center. Mark a cross ( X ) on one side of the sheet of paper as shown in figure.

Hold the sheet in front of your eyes with the ‘X’ mark at the bottom and look for the pole star through the hole. Once you have located the pole star, check in which direction the Great Bear and Cassiopeia lie.
Write ‘G’ for Great Bear and ‘C’ for Cassiopeia on the paper in the directions in which you see each of the constellations. Mark the timing at which you made your observation in both cases.
Choose a nearby tree or house as a reference point. Draw a picture of your reference point on the paper sheet taken, clearly indicating its location. Repeat your observations at one hour intervals. Ensure that you are standing on the same spot each time you look at the stars.
Write G, C in the direction of the position of the great bear and Cassiopeia during each observation and note the time of the observation next to the letters G and C.
Using the tree or house you have chosen as your reference point, check whether the position of the pole star has changed or not. If it has changed, note the changed position.
Repeat this activity as many times as possible, the minimum being four times. But ensure that the ‘X! mark on your sheet of paper remains at the bottom during all your observations.

a) Do the positions of the stars change with time?
Answer:
Yes, they will change.

b) Does the position of the pole star also change with time?
Answer:
No, it will not change with time.

c) Does the shape of the great bear and Cassiopeia change with time or does the position of the entire constellations in the sky change?
Answer:
The position of entire constellation changes.

d) What kind of path do these constellations trace in the sky?
Answer:
They traced in northern sky.

Activity – 8

Question 8.
Why does the pole star appears fixed at one point?
Take an umbrella and open it. Make about 10-15 stars out of white paper. Paste one star at the position of the central rod of the umbrella and others at different places on the cloth near the end of each spoke.

Now rotate the umbrella by holding its central rod in your hand. Observe the stars on the umbrella.
a) Is there any star which does not appear moving? Where is this star located? Is it located where the rod of the umbrella holds the cloth of the umbrella?
Answer:
Yes, it is located where the rod of the umbrella holds the cloth of the umbrella.

b) On similar lines, if there were a star located where the axis of rotation of the earth meets the sky, could this star is also be stationary?
Answer:
Yes, that is the reason pole star does not move even though all stars appear that they are moving because of rotation of earth.

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 3 Story of Microorganisms 2

AP State Syllabus 8th Class Biology Important Questions 3rd Lesson Story of Microorganisms 2

8th Class Biology 3rd Lesson Story of Microorganisms 2 1 Mark Important Questions and Answers

Question 1.
What are antibodies?
Answer:
Whenever a disease causing microorganisms enter in our body, it produces some de¬fenders to fight against them, these are called antibodies.

Question 2.
Which one is better to take antibiotics or vaccines?
Answer:
Vaccines are better than antibiotics when the disease is prevented by vaccine.
Ex: Tuberculosis, Tetanus, etc.

Question 3.
What questions do you ask on role of mosquitoes and houseflies in spreading the diseases like Malaria and Swine flu?
Answer:

1. How can we be safe, without affected by malaria and typhoid?
2. Which organisms spread diseases like malaria and typhoid?

Question 4.
What is ‘Triple Antigen Vaccine’?
Answer:
D.P.T vaccine which prevents

1. Diptheria
2. Pertusis (Wooping cough)
3. Tetanus

Question 5.
What is Tet – vac?
Answer:
Tet – vac is the vaccine that is used to prevent Tetanus.

Question 6.
What is M.M.R vaccine?
Answer:
M.M.R is the vaccine that prevents the

1. Measles
2. Mumps
3. Rubella

Question 7.
Name the vaccine that prevents T.B.
Answer:
B.C.G (Bacillus Cardio Gram)

Question 8.
What is the mode of transmission of Dengue disease?
Answer:
Aedes Mosquitoes spread Dengue disease.

8th Class Biology 3rd Lesson Story of Microorganisms 2 2 Marks Important Questions and Answers

Question 1.
Mention different questions to know about antibiotics.
Answer:

1. What are antibiotics?
2. In which year penicillin was announced as antibiotic?
3. Can antibiotics destroy the viruses?
4. Write different types of antibiotics.

Question 2.
Prepare different questions to know the importance of vaccines.
Answer:

1. Name the scientist who invented vaccines first.
2. What type of materials used for preparation of vaccines?
3. Name the vaccine which is used to prevent rabies.
4. Name the disease which is eradicated by vaccine.

Question 3.
Ask different questions about the significance of microbes.
Answer:

1. Name different nitrogen fixing microbes.
2. Can all microbes useful to mankind?
3. What will happen if vaccines are not invented?
4. Write about significance of microbes.

Question 4.
Make a sketch of Nostoc.
Answer:

Question 5.
How is preservation of food helps us?
Answer:

1. Preservation prevents spoilage of food.
2. It helps us to store food for a longer time without spoilage.
3. Variety of food items may be available in off seasons also.

8th Class Biology 3rd Lesson Story of Microorganisms 2 4 Marks Important Questions and Answers

Question 1.
Which one is better to take antibiotics or vaccines? Why?
Answer:
Antibiotics are small molecules or compounds that are effective in treating infections caused by organisms such as bacteria, fungi and protozoa. Some antibiotics act by killing the bacteria while others prevent the bacteria from multiplying, leaving your own immune system to ‘mop them up’.
Vaccines are dead or inactivated organisms or compounds that are used to provide immunity to a particular infection or disease.
Vaccines are used to prevent infection, particularly viral infections. Vaccines are produced from portions of viruses or viruses that are rendered harmless.
The killed or modified virus is introduced into the body where it stimulates part of the body’s natural defenses against infection without causing the illness itself.
Because of this, if the body is exposed to the specific virus in the future, it will recognize it and can fight the infection off much more quickly and effectively, meaning that you don’t succumb to the illness.
Hence vaccines are better than antibiotics when the disease is prevented by vaccine. Ex: Tuberculosis, Tetanus, etc.

Question 2.
Refrigerator helps us in saving health and money. Can you explain?
Answer:
Food and drink, being organic in origin, does not last forever. Shortly after food is bought or prepared it will begin to spoil, quickly becoming inedible through the effects of bacteria. By lowering the temperature of the food through refrigeration, you can slow or even temporarily halt the effects of bacteria, making the food stay edible longer.we can also transport fruits vegetables and other food items up to long distances by using refrigerators. Refrigerator is more useful to keep vaccines and medicines for long time. Hence we can save money and as well as health.

Question 3.
Take root nodules of any pulse or leguminous plants crush on a slide, and draw a rough sketches of what you observe under microscope.
Answer:

Question 4.
Can you give some important key points you noticed that scientists followed in their inventions and discoveries?
Answer:
Invention of microscope is most important one to find out microorganisms. Basing on this several inventions were made, which break the unsolved problems since 400 years. This credit goes to Antonie van Leeuwenhoek who invented single lens powerful microscope, which could magnify the object 300 times. His curiosity and skill of making powerful lenses were the secrets of this invention of powerful microscope.
Dr. Alexander Flemming observed some fungi were preventing the growth of bacteria in his experiments. He separated the substances released by the fungus and tested it on some other disease causing bacteria. This substance also killed many other diseases causing bacteria and named it as Pencillin. The discovery of pencillin paved the way to the discovery of many antibiotics like streptomycin, erythromycin etc.
After several attempts Ross suddenly realized that he used the wrong species of mosquitoes in his experiments. His assistant brought larvae, which hatched to several dappled winged mosquitoes. Delighted with this capture Ross identified Anopheles mosquito is the host for malarial parasite.

Question 5.
Which invention is most important one related to microorganisms? Can you explain the reasons why it is so important?
Answer:
Invention of microscope is most important one to find out microorganisms. Basing on this several inventions were made, which break the unsolved problems since 400 years. This credit goes to Antonie van Leeuwenhoek who invented single lens powerful microscope, which could magnify the object 300 times. His curiosity and skill of making powerful lenses were the secrets of this invention of powerful microscope. Later several microbes were identified by using microscopes. This provides a good source to recognize several diseases and treatment by vaccines and antibiotics.

Question 6.
What are antibodies? When do they develop? How they help us?
Answer:
Whenever a disease causing microorganisms enter in our body, it produces some defenders to fight against them, these are called antibodies. The lymphocytes of white blood cells develop antibodies against to the antigen of pathogen. Antibodies fight the disease causing microorganisms and make resistant to particular strains. Antibodies are used by the immune system to identify and neutralize foreign objects such as viruses and bacteria.

Question 7.
If there are no microorganisms on the earth what will happen?
Answer:
Microorganisms are present everywhere, they are to be found in air, water, soil within the bodies of animals and plants. Some microorganisms are very useful and help us in many ways while some of them are harmful. Microorganisms are most essential to maintain inorganic and organic cycles, to give freshness to the nature by degrading waste organic matter and as well as to fight against harmful microorganisms. Hence no life will be sustained in the nature if there are no microorganisms on the earth.

Question 8.
Prepare a table showing some of plant diseases, causative microorganisms and mode of transmission.
Answer:

Name of the plant disease	Causative microorganisms	Mode of transmission
1. Citrus canker	Bacteria, Xanthomonoss citri	Air
2. Red rot of sugarcane	Fungi	Air, seedlings
3. Tikka disease of groundnut	Fungi	Air, seeds
4. Tobacco mosaic	Virus	Insects
5. Smut disease of rice	Fungus	Air

Question 9.
If there are no microorganisms on the earth what will happen?
Answer:

1. If micro organisms are not present on earth the earth will be full of dead organisms and plants.
2. The plants can not fix the atmospheric nitrogen in the soil.
3. We can not get fermented products.
4. The life becomes impossible on the earth.

8th Class Biology 3rd Lesson Story of Microorganisms 2 Important Questions and Answers

Question 1.
Many people to. a colony are suffering from ‘Cholera’. What do you think could be the reason?
Answer:

1. The main reasons for the spread of cholera is consumption of contaminated food and water. House flies rapidly spread this disease among people.
2. I would imagine that people were not following personal hygienic practices before consuming food and water.
3. Perhaps people might not be keeping their surroundings clean and hygienic.
4. Perhaps the people might have poor sanitary conditions.

Question 2.
Suggest any two methods of fish preservation.
Answer:

1. Drying
2. Smoking
3. Canning
4. Chilling

Question 3.
What is symbiosis? Give two examples for it.
Answer:

1. In Greek language, symbiosis means “living together”.
2. Symbiosis is any type of a close and long term biological interaction between two different biological organisms in which both are benefited.
3. Examples for symbiotic relationship is Rhizobium. Rhizobium bacteria is living in the root nodules of legume plants.
4. Rhizobium fixes the atmospheric nitrogen in the form of nitrates which are very essential for the growth of plants. Inturn legume plants provide shelter for Rhizobium. Here, both are benefited.
5. Another example for symbiosis is Lichens. Here, we can see the symbiotic relationship between Algae and Fungi.

Question 4.
In an experiment if we keep the dosa dough in Bacillus free chamber, what changes can you observe in the dosa dough after one day?
Answer:

1. Fermentation of dosa dough will not take place.
2. The volume of the dosa dough will not increase and it will not turn into spongy texture.

Question 5.
Classify the given below microorganisms into useful and harmful microorganisms.
Plasmodium, Lactobacillus, Rhizobium, Pencillium, Yeast, Virus.
Answer:
Useful microorganisms:

1. Lacto bacillus
2. Rhizobium
3. Pencillium
4. Yeast

Harmful microorganisms:

1. Plasmodium
2. Virus.

Question 6.
What will happen if we add butter milk to chilled milk?
Answer:
If we add a few drops of butter milk to chilled milk 1) the milk will not turn into curd. It is because, cold milk won’t provide the conditions to grow lactobacillus. Hence, curd will not be formed.

Question 7.
If you are going to conduct a quiz on micro-organisms, what type of questions do you prepare for the quiz programme?
Answer:

1. Can you name the scientist who discovered the pencillin?
2. Name the bacteria that converts the milk into curd.
3. Can you name the food items that can be preserved through pasteurisation?
4. Can you name the microorganism which is very helpful in the preparation of alcohol?

Question 8.
What is the name of the nitrogen fixation bacteria in the root nodules?
Answer:
Rhizobium

Question 9.
What precautions do you take to avoid diseases?
Answer:

1. We should consume boiled, purified water and healthy food daily.
2. Keep our surroundings neat and clean.
3. We should take vaccines to prevent different diseases.
4. We should practice personal hygiene and good sanitary habits.

Question 10.
Defecation in open areas spreads micro-organisms easily. Write some slogans to conduct a rally to protect us from micro-organisms.
Answer:

1. Keep your country clean by keeping your area clean.
2. Stop being so open….. else everything is broken.
3. Use a toilet. Don’t let anything spoil it,
4. Use a toilet – to achieve Swach Bharath.

Question 11.
Draw a table of microorganisms and its diseases.
Microorganisms : Virus, Bacteria, Protozoa, Arthropods.
Disease: Scabies, Malaria, Polio, Typhoid.
Answer:

Microorganism	Disease
1. Virus	Polio
2. Bacteria	Typhoid
3. Protozoa	Malaria
4. Arthropods	Scabies

Question 12.
Why is the idly or dosa batter prepared one day before?
Answer:
If we prepare idly or dosa batter one day before, fermentation occurs in it, carbondioxide gas fill the batter increasing it’s volume and makes it spongy.

Question 13.
Read the following passage and answer the following questions.
When an infected person sneezes or coughs, the pathogens enter the air. When this air containing pathogens enters into the body of a healthy person, it may cause cold. These type of diseases which spread from infected people to healthy ones are known as “communicable diseases”. These get spread through air, water, food or through physical contact of infected person or through insects like houseflies and mosquitoes. Common cold, conjunctivitis, typhoid, smallpox, chickenpox, swine flu, tuberculosis are some examples of communicable diseases. Some insects and animals carry diseases causing microorganisms. They are called as ‘vectors’. The microorganism ‘plasmodium’causes malaria. The female Anopheles mosquito carries plasmodium and thus is a vector. Mosquitoes are vectors for other diseases as well. By controlling mosquitoes, we can prevent dis¬eases caused by them. Mosquitoes breed in stagnant water. We should be careful not to let water collect anywhere in our surroundings, including left over waste pots, waste flower pots, tyres, bowls etc.
a) What are communicable diseases? Give examples.
b) What are vectors?
c) Name the vector which spreads malaria.
d) How do you prevent spread of malaria?
Answer:
a) The diseases which spread from infected people to healthy ones are known as “communicable diseases”.
Eg: Conjuctivitis, Common cold, Smallpox, Rubella, Typhoid, etc…
b) The insects and animals which carry disease causing microorganisms are called as “vectors”.
c) Female Anopheles mosquito.
d) By controlling mosquito population.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 10 Reflection of Light at Plane Surfaces Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 10th Lesson Reflection of Light at Plane Surfaces

8th Class Physical Science 10th Lesson Reflection of Light at Plane Surfaces Textbook Questions and Answers

Improve Your Learning

Question 1.
State the laws of reflection of light (OR)
Name the laws of reflection of light
Answer:
Laws of reflection:

1. When light gets reflected from a surface, the angle of reflection is equal to the angle of incidence, i.e., ∠i = ∠r.
   
2. The incident ray, the normal at the point of incidence and the reflected ray lie in the same plane, i.e., AO, ON, OB are in same plane.

Question 2.
How do you verify the 1st law of reflection of light with an experiment?
(OR)
Raghu found that for a plane mirror angle of incidence is equal to the angle of reflection. Write the experiment to prove this fact. (OR)
Prove: ∠i = ∠r (LAB ACTIVITY – 1)
Answer:
Aim: Verification of first law of reflection.
Required materials: Mirror strip, drawing board, white paper, pins, clamps, scale and pencil.
Procedure:

1. Take a drawing board and fix a white paper on it with the help of clamps.
2. Draw a straight line AB at the centre of the paper and also a normal (ON) to AB at the point ‘O’.
3. Draw a straight line PQ making certain angle (angle i) with ON.
4. Fix two pins at P and Q on the paper vertically.
   
5. Observe the images of pins – P’ of the pin P and Q’ of the pin Q, in the mirror kept along the line segment AB.
6. Fix two more pins R and S such that they are in the same line as that of P’ and Q’.
7. Join R, S and 0 as shown in figure.
8. Measure the angle between RS and ON (angle of reflection).
9. We will find that ∠i = ∠r. (angle of incidence = angle of reflection)
10. Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.
11. We can find angle of incidence = angle of reflection in all these cases.
    Thus first law of reflection is proved.

Question 3.
How do you verify the 2nd law of reflection of light with an experiment?
(OR)
John found that incident ray, reflected ray and normal drawn to surface lie on the
same plane. What are the apparatus required for this experiment? How are you able to prove this fact experimentally?
Answer:
2nd Law of reflection: The incident ray, the reflected ray and normal all lie in the same plane.

1. As shown in the figure, a light ray incident on a plane mirror and touches at a point ‘O’. Here AO is called incident ray.
2. When a ray of light falls on a mirror, the mirror sends it back in another direction OB. Here OB is called reflected ray.
3. Normal is a line which is perpendicular to the mirror at the point of incidence. So the line ON’ is the normal to the mirror surface at point ‘O’.
   
4. Here the incident ray (AO), the reflected ray (OB) and the normal (ON) all lie in the same plane of the paper.
   Hence 2nd law of reflection is proved.

Question 4.
Explain the image formation by pin hole camera with the help of the diagram.
(ACTIVITY – 1)
Answer:

1. Draw a ray diagram of the formation of an image in a pinhole camera.
2. Observe the flame of a candle with a pinhole camera making a big hole to it.
   
3. We can understand that the light rays coming from the top of the candle flame fall at different points on the screen.
4. Similarly, the rays coming from bottom of the candle points on the screen.
5. Thus, we get blurred image on the screen due to the big hole of the camera.

Question 5.
Find the plane of the reflection experimentally for the incident ray which passes through the heads of the pins pierced in front of the mirror.
(OR)
Sudheer wants to verify the laws of reflection. What apparatus he requires to prove them? State the laws of reflection and write the experimentation process he follows.
Answer:
Aim: Verification of laws of reflection.
Required material: Mirror strip, drawing board, white paper, pins, clamps, scale and pencil.
Procedure:

1. Take a drawing board and fix a white paper on it with the help of clamps.
2. Draw a straight line AB at the centre of the paper and also a normal (ON) to AB at the point ‘O’.
3. Draw a straight line PQ making certain angle (∠i) with ON.
4. Fix two pins at P and Q on the paper vertically.
   
5. Observe the image P’ of the pin P and Q’ of the pin Q, in the mirror kept along line segment AB.
6. Fix two more pins R and S such that they are in the same line as that of P’ and Q’.
7. Join R, S and O.
8. Measure the angle between RS and ON (∠r) .We will find ∠i = ∠r.
9. Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.
10. We find that each case angle of incidence is equal to angle of reflection. That is first law.
11. We can find that the incident ray is the ray which is passing through points P and Q touching the paper.
12. The reflected ray is the ray which is passing through the points R and S touching the same paper and ON is the normal to the mirror at O. All lie in same plane. That is second law which states incident ray, reflected ray and normal drawn to plane lie in the same plane.

Question 6.
Have you ever observed the image of the sky in rain water pools on earth? Explain the reflection of light in this context.
Answer:
Surface of the rain water pool acts as a plane mirror, because of its smooth surface. The light rays from the sky and clouds incident at this surface and reflect. Hence, the images of the sky and clouds appear in the rain water pools.

Question 7.
Discuss the merits and demerits of using mirrors in building elevation.
(OR)
What are the advantages and disadvantages of using mirrors in building elevation?
Answer:
Merits:

1. The mirrors used in elevating building are tough, reinforced and laminated glasses so they provide safety to the building.
2. They make the building attractive.
3. They absorb heat energy, so they cool inside the building.
4. If we use plane mirrors in building elevation it is easy to wash with water and no need of regular painting.

Demerits:

1. Elevation of buildings with mirrors is not suggestable.
2. These mirrors reflect sun rays at day time and reflects lighting from near by electrical bulbs at night time, which causes confusion and disturbance for the vehicles and people who are running on the nearby roads lead to accidents.
3. Birds like sparrows, crows will get confusion while flying on roads.
4. They are also not safe enough to the buildings, which causes easy access to thieves.
5. This glass elevation is not environmental friendly, because natural air does not enter into the building.
6. They are easy to break and cause cuts and wounds.

Question 8.
If a ray incidence normally on a plane mirror, what will be the angle of reflection.
Answer:
If a ray incidence normally on a plane mirror, the angle of reflection will be zero.

Question 9.
Why does the image in plane mirror suffers lateral inversion?
Answer:
The light rays which come from our right side get reflected from the plane mirror reach our eye. Our brain feels that the rays is coming from the inside of the mirror. That is why our right side looks like left side in the image. This is called right-left inversion or lateral inversion.

Question 10.
Draw a ray diagram to understand the formation of image for a pointed object by a plane mirror explain it.
Answer:
Observe the figure. ‘O’ is a point object.

Some rays from ‘O’ reach the mirror and get reflected. When we look into the mirror, the reflected rays seem to be coming from the point T. So, point I is the image of point object ‘O’.

Question 11.
In the adjacent figure, AO and OB are incident and reflected rays respectively angle ∠AOB = 90°. Find the values of angle of incidence and angle of reflection.

Answer:
We know that angle of incidence is equal to angle of reflection.
i = r …….. (1)
From the figure, ∠AOB indicates i + r = 90°
From (1)
⇒ i + i = 90°
2i = 90°
⇒ i = 90/2 = 45°
⇒ i = r = 45°
Angle of incidence i = 45°; Angle of reflection r = 45°.

Question 12.
Hinduja stands in front of a plane mirror at a distance of 5 m. from the mirror and observes her image in the mirror. If she moves 2 m. towards the plane mirror, then what will be the distance between Hinduja and his image?
Answer:
The distance between plane mirror and Hinduja = 5 m
The distance between plane mirror and Hinduja after moving 2 m towards mirror
= 5 – 2 = 3 m …….. (1)
The distance between plane mirror and Hinduja’s image after moving = 3 m …….. (2)
The distance between Hinduja and her image after moving = (1) + (2) = 3m + 3m = 6m.

Question 13.
Explain diagramatically the Image of letter ‘B’ in a plane mirror.
Answer:

Question 14.
Why can’t we see our image in a white sheet of paper though it reflects light?
Answer:
By microscopic observation, we can find up and downs over surface of a paper. Hence paper is not a smooth fine surface. Even though sheet of white paper reflects the light rays, they do not form an image of an object.

Question 15.
Observe the below figure. AB and BC are two plane mirrors arranged at 120°. A ray incidents at and angle 55° on AB. Find the value of ‘x’

Answer:
Let us say, angles a, b, c, d as shown in the figure. From the figure, a = 55° [∵ i = r]
a + b = 90° [. Normal to the plane]
55° + b = 90°
⇒ b = 90° – 55° = 35°
120° + b + c = 180° [∵ Total of angles in a triangle]
120° + 35° + c = 180°

⇒ c = 180° – 155° = 25° c + d = 90° [∵ Normal to the plane]
25° + d = 90°
⇒ d = 90° – 25° = 65°
d = x [∵ i = r]
∴ x = 65°

Question 16.
The size of the image in the mirror seem to be decreased when you move the object towards your eye from the mirror. Draw the diagram showing angles depicting the situation.
Answer:

Question 17.
Collect the information about “Situations using the plane mirrors and prepare the report.
Answer:
Plane mirrors have many uses.

1. Periscopes: They are used in periscopes to see bends and corners. It is used for observing enemy movements from trenches without any danger of being seen. Sailors on submarines use periscopes to see things above the water level.
2. Kaleidoscopes: Kaleidoscope is a toy that uses light and mirrors to reflect objects and create beautiful, fascinating repeating patterns.
3. Security: Mirrors are used while looking for explosives underneath a vehicle. Even these mirrors are used in shops to keep an eye on the customers. Mirrors are also used in blind turns of busy roads to see the vehicles coming from the other side.
4. Telescopes and Microscopes: Plane mirrors are used in many scientific applications like telescopes and microscopes.
5. Dressing mirrors: Plane mirrors are used in dressing tables to see ourselves, while dressing, shaving, etc.
6. Ophthalmic doctors: They use plane mirrors to increase the distance of the eye test chart while examine the eye of a patient.
7. Docorating mirrors: Plane mirrors are used to decorate the building for elivations. Some shops also used plane mirrors to get multiple images of the items in their shops.

MULTIPLE CHOICE QUESTIONS
1. Angle of incidence = Angle of reflection. This rule is explained by …………… principle        ( )
A) Fermat
B) Newton
C) Archemedes
D) Pascal
Answer: A

2. Which of the following letters doesn’t suffer lateral inversion?         ( )
A) C
B) O
C) B
D) N
Answer: B

3. A ray of light incidents on a plane mirror at an angle of 90° to its surface. What will be the angle of relfection?   ( )
A) 0°
B) 90°
C) 450°
D) 180°
Answer: A

4. If we move an object away from the plane mirror the size of images seems to be     ( )
A) increases
B) decreases
C) of the same size
D) image can’t be seen
Answer: B

5. Which of the following is incorrect with respect to the image in a plane mirror?     ( )
A) Image is erect
B) size of the image is same as the size of object
C) laterally inverted
D) image is real.
Answer: D

6. An object is placed 7cm distance from the plane mirror then distance of image is      ( )
A) 3.5 cm
B) 14 cm
C) 7 cm
D) 21 cm
Answer: C

8th Class Physical Science 10th Lesson Reflection of Light at Plane Surfaces InText Questions and Answers

8th Class Physical Science Textbook Page No. 134

Question 1.
How can we get the image of a big building in a small mirror?
Answer:
Light rays travel in all directions from one object. Light rays coming from a building incident on the small area of a plane mirror and reflect. These reflected rays reach our eye. We see the image of the building in the mirror.

Question 2.
Can we get the image formed by a plane mirror on a screen?
Answer:
Cannot.

Question 3.
Why is there lateral inversion, when we look into a mirror?
Answer:
Our brain feels that the rays is coming from the inside of the mirror.

Question 4.
Why is the angle of reflection equal to the angle of incidence when a light ray gets reflected from a surface?
Answer:
Light always choose the path of least time to travel.

8th Class Physical Science Textbook Page No. 138

Question 5.
Is the angle of reflection equal to the angle of incidence in all cases?
Answer:
Yes.

Question 6.
Do the two rays and the normal lie in the same plane? If yes, which is that plane?
Answer:
Yes, plane of paper.

Question 7.
In which plane will the incident ray, reflected ray and the normal lie?
Answer:
Plane touching the heads of pins and parallel to the plane of paper.

Question 8.
How will the incident ray be?
Answer:
Incident ray touching heads of the pins (P and Q) and make some angle with plane of the paper.

Question 9.
How will the reflected ray be?
Answer:
Reflected ray will make some angle with plane of the paper.

Question 10.
How will the normal be?
Answer:
The normal will also make same angle as incident and reflected rays.

Question 11.
How will the plane of reflection be?
Answer:
Plane of reflection make some angle (which is equal to plane of the paper and incident ray) with plane of the paper.

Question 12.
How does a mirror form the image of a pin or any object? Let us discuss.
Answer:
The rays coming from the pin get reflected from the mirror and seem to be coming from the image in the mirror.

8th Class Physical Science Textbook Page No. 139

Question 13.
What is the size of the image compared to the size of the object?
Answer:
Size of the image is equal to size of the object.

Question 14.
What do you say about the size of the image compared to the size of the object? Move the object towards your eye. What do you observe?
Answer:
Size of the image is same as size of the object. If we move the object towards our eye, size of the image of the object seems to be decreased.

Question 15.
Is the size of the image decreasing or increasing?
Answer:
Decreasing.

8th Class Physical Science Textbook Page No. 140

Question 16.
Why does an image suffer lateral (right-left) inversion? See the figure.

Answer:
Our brain feels that the rays are coming from the inside of the mirror and image is opposite to us. In this way image suffer lateral inversion.

Question 17.
What do you understand from the figure?
Answer:
The light rays which come from our right ear get reflected from the plane mirror and reach our eye. Our brain feels that the ray is coming from the inside of the mirror. That is why our right ear looks like left ear in the image.

Think, Discuss and Write

8th Class Physical Science Textbook Page No. 135

Question 1.
Does the explanation on pinhole match with your observation?
Answer:
Yes, it matches with my observation.

Question 2.
What happens if the hole Is much bigger, i.e., equal to the size of the flame?
Answer:
The image is extremely blurred.

Question 3.
If so, can we get the image of flame on the screen of pinhole camera? Why?
Answer:
No. Because the light rays coming from the top of the flame and bottom of the flame fall at different points on the screen. So it is blurred and is not formed on screen.

Question 4.
What happens if we observe the same flame with the same pinhole camera from a long distance?
Answer:
We may observe not only the flame, but the blurred image of entire candle.

Question 5.
What happens if we made two holes to pin hole camera?
Answer:
Two images will be formed.

8th Class Physical Science 10th Lesson Reflection of Light at Plane Surfaces Activities

Activity – 2

Question 1.
Which grain on the ground that a smart crow on tree A pick to reach B in short time (Shortest path)? Explain. (OR)
How do you support your answer to “When light gets reflected from a surface, it selects the path that takes the least time”? (OR)
Explain Fermat’s principle by using an activity.
Answer:

1. The crow can pick the grain from any point on the ground, but the condition is selecting the shortest path.
2. Let the speed of the crow is constants –
3. Observe some of the paths in figure.
4. To compare the lengths of these paths ACB, ADB, AEB and AFB, make the duplicates of them at point G as shown in figure.
5. In the figure CB = CG,
   ∴ The length of path ACB = AC + CB = AC + CG = ACG
6. Similarly length of the path ADB = length of the path ADG Similarlylength of the path AEB = length of the path AEG Similarly length of the path AFB = length of the path AFG
7. By observing the above paths, we will notice that AEG is the shortest path among all the paths, because it is the straight line distance between points A and G.
8. So the smart crow will pick the grain from point E.

Activity – 3

Question 2.
Look at the following figure.
Suppose if you have been given a plane mirror strip, what will you do to obtain figures as shown below figure (b) using mirror strip and the above figure (a)?

Answer:
The place of mirror that should be place on the figure vertically has been shown here under by a line.

In the above diagrams, line indicates the position of mirror to be kept to get the required shapes.