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AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 8 Combustion, Fuels and Flame Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 8th Lesson Combustion, Fuels and Flame

8th Class Physical Science 8th Lesson Combustion, Fuels and Flame Textbook Questions and Answers

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Question 1.
Give four examples of combustible materials.
Answer:

1. Petrol
2. Diesel
3. Kerosene
4. Alcohol

Question 2.
Give four examples of non-combustible materials.
Answer:

1. Sand
2. Clay
3. Iron
4. Steel

Question 3.
Why should not we store spirit or petrol near our living place?
Answer:
Spirit or petrol has low ignition temperature. So they turn into gas at room tempera¬ture. So they are highly inflammable that means they easily catch fire at room temperature. So in order to avoid fire accidents we should not store spirit or petrol near our living place.

Question 4.
Give an example of a good fuel. How do you choose that fuel? Explain.
Answer:
The example for good fuel is CNG.
The characteristics of good fuel.

1. It should be cheap.
2. It should be readily available.
3. It should be readily combustible.
4. It should be transported easily.
5. It should have high calorific value.
6. It should not produce gases or residue that pollute the environment.

CNG possess all these characteristics so it is an example for good fuel or ideal fuel.

Question 5.
The oil tires should not be sprayed with water. Why?
Answer:
We should not spray water on oil fires because water is heavier than the oil, it sinks below the oil and oil keeps burning on the top. So water is not suitable for oil fire accidents.

Question 6.
What precautions are to be taken while pouring water on fire?
Answer:

1. Put off the electric mains.
2. Do not pour water on fires caused by electricity water containing dissolves salts is a good conductor of electricity.
3. Do not pour water on fires due to petrol and oil because water is more denser the u oil and petrol.

Question 7.
Why a wick is not used in gas burners ?
Answer:
Wax in the candle melts when it is lighted by a match and a little wax forms vapour. This vapour combines with oxygen in the air to form flame. The heat of the flame melts more of the wax from the top of the candle. The melted liquid wax move upward through the thread. It also changes to vapour when it reaches the top the wick and burns w’ h the flame.
Wick is not required in gas burners because LPG has low ignition temperature so it is easily convert into vapour state.

Question 8.
Water is not used to control fires involving electrical equipment. Why?
Answer:
Water is not used to control fires involving electric equipments because water is good
conductor of electricity (water having dissolved salts) so it may conduct electricity and harm those trying to douse the fire.

Question 9.
Give supporting arguments for both the statements (1) fire is useful (2) fire is harmful.
Answer:
Fire is useful:

1. Fire is useful in cooking food.
2. Fire is used in preparing different types of jewellery with gold and silver.
3. Fire is utilized in making different types of articles with metals and plastics.
4. The heat energy produced from fire of coal used to produce electricity.

Fire is harmful:

1. During fire accidents fire can burn human organs and tissues causing severe damage to mankind, sometimes the people may die due to severe burns.
2. During fire accidents the fire not only kill people but lot of damage to articles, equipments in the house.
3. Fire can burn the forests in summer which may be harmful to animals present in the forest.

Question 10.
What would happen if oxygen stops to support combustion? – Make a guess. And if it is the situation for what other works fuels are useful?
Answer:
If oxygen stops to support combustion there is no other gas which will support combustion. Then fossil fuels are not useful in producing heat, energy and electricity.
So we should have to prefer alternative sources of energy like solar energy, wind energy, tidal energy, biomass energy, geothermal energy, etc. for our energy needs.

Question 11.
Let us assume that you are on the moon. If you try to focus sunlight on a paper using magnifying glass, does the paper catch fire? or not? Why?
Answer:
No, moon reflect entire sunlight falls on the surface because it acts as perfect reflector. Whereas earth is also acts as reflector but green house gases present in atmosphere absorbing the sunlight and resending on earth. So paper can be burnt on earth by using magnifying glass but it is not possible on moon.

Question 12.
Can you heat water in a paper vessel? How is it possible?
Answer:
In order to find the answer we have to do an experiment.

Take two small paper cups. Pour water in one of the cups. Put the two cups on different tripod stands and heat both of them using a candle shown in the figure. One cup burns quickly and other does not.
The reason is when heat is supplied to cups, the heat received by second cup is transferred to water
in it. The water in this cup prevents the paper to reach its ignition temperature and hence it does not burn. So water can be heated in a paper vessel upto ignition temperature of paper.

Question 13.
“Is combustion possible without the supply of oxygen”? Discuss with your teacher.
Answer:
No, combustion is not possible without oxygen because it is a reaction of material with oxygen that is an oxidation process. For example, carbon compounds react with oxygen and form carbon-dioxide and water. So no combustion reaction is possible without oxygen.

Question 14.
Explain giving reasons: In which of the following situations water will get heated in a shorter time?
a) Srikar kept water beaker near the wick in the yellow part of a candle flame.
b) Sonu kept water beaker in the outermost part of the flame.
Answer:
In the second situation water will get heated in a short time in the outermost part in the flame complete combustion takes place so which is hottest part whereas yellow part is in the middle zone of candle where partial combustion takes place and it is moderately hot.

Question 15.
List the ways adopted by fire fighters to combat fires.
Answer:
Ways adopted by fire fighters:

1. The fire fighters immediately put off the electric mains and start spraying water on the fire. The water spray cool the combustible material below the ignition tempera¬ture. This prevents fire from spreading. Then the heat turns the water into vapours which surround the burning material and prevent supply of oxygen to the burning material. So the fire extinguishes.
2. For electrical fire accidents or fire accidents involving oil and petrol water is not useful. So fire fighters use carbondioxide. It is heavier than oxygen and does not affect the electric equipment.

Question 16.
Collect information available on different fuels. Find out the cost per kg and compare the cost with calorific value. Prepare report on that.
Answer:

From the table we will observe CNG has least price and also comparatively equal calorific value with other fuels and also it is less pollutant and easily transportable. So from the report we say CNG is preferable as fuel.

Question 17.
Draw the diagram of candle flame and label all the zones. (OR)
Draw the diagram of structure of flame and label the parts. In which zone incomplete combustion takes place? (OR)
Draw a diagram of candle flame and label all the zones. What happens in the dark zone of a flame?
Answer:

In the dark zone wax gets vapourised and it is least hot part, (or)
In black zone in complete combustion takes place.

Question 18.
Where do you find spontaneous combustion and rapid combustion in your daily life?
Answer:
Spontaneous combustion is observed in burning of match stick. When the match stick is struck against the rubbing surface the red phosphorous converts into white phosphorous which immediately react with potassium chlorate in the match stick head to produce enough heat to ignite antimony sulphide and start the combustion.
Rapid combustion is observed in gas stoves. When we turn the nob of the gas stove in the kitchen and bringing a burning match stick near to it. The gas burns rapidly and produce heat and light.

Question 19.
How do you organize your daily works with fuels to conserve bio-diversity?
Answer:

1. I would use bicycle to travel short distances which consumes fuel.
2. I would go to school or office (long distance) in a public vehicle like bus which will consume fuel.
3. I will drive at a constant and moderate speed as far as possible which will consume fuel.
4. I switch off the engine at traffic lights or at a place where I have to wait which will consume fuel.
5. I ensure correct tyre pressure which will consume fuel.
6. I ensure regular maintenance of the vehicle which decreases the harmful gases.
7. I will clean gas burners regularly which decreases pollution.
8. I will cook with sufficient water which will consume fuel.
9. I would not prepare fries which take more time.
10. I will use CNG in place of petrol or diesel which is less pollutant.
    The above steps not only reduce the consumption of fuel and also decrease the air pollution. These steps of preserving fuels helps the mankind from pollution there by helps the bio-diversity.

Question 20.
How do you feel about “Fuels have become a part of human life”
Answer:
I feel that fuels are essential part of human life in their day to day life. Starting from the morning before they going to sleep they would found application of fuels. In the morning for breakfast we need fuel for cooking. For seeing TV or working with computer we need fuel because they run by electricity from thermal power (coal). If we want to go to school or office we use vehicle which required fuel. Every electrical articles like fans, mixies works by taking electricity from coal. So we conclude that fuels are essential part of human life.

Question 21.
It is difficult to bum a heap of green leaves but not a heap of dry leaves. Explain why?
Answer:
Green leaves contain water has high ignition temperature. So it will not burn whereas dry leaves does not contain water. So their ignition temperature is low. So they burn during summer.

Question 22.
In a few years the fuels on earth will be exhausted. Think, what would happen to human civilization? (OR)
In few years the fuel on earth will be exhausted. Predict the consequences.
Answer:
If people unable to use alternative sources of energy then lack of fuels drastically affect the human civilization. The consequences of lack of fuel.

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 of people on earth is miserable. The people once again go back to stone age where there is no availability of any facilities.

Question 23.
Use of more fuels in our daily life causes air pollution and it is harmful to human being and the other life on earth. Suggest some remedies to avoid this.
Answer:
Remedies to avoid air pollution:

1. Look for alternative sources of energy like wind energy, solar energy, tidal energy which does not produce pollution.
2. Try to minimise the use of fuels that is for travelling short distances use bicycles and try to go by bus (public transport) for offices which will minimise the use of fuels and there by air pollution.
3. Ensure regular maintenance of vehicle and engine which will release the less quantity of harmful gases there by decrease of air pollution.
4. Use CNG (compressed natural gas) as fuel as it is less pollutant and release small quantity of harmful gases.

Question 24.
Project work: Collect information about the experiments of Joseph Priestly. Write a two page report describing Priestly’s experiments proving that oxygen is needed for burning.
Answer:
In August 1774, Priestly isolated an air to be completely new, but he did not have an opportunity to pursue the matter because he was about to tour Europe. While in Paris Priestly managed to replicate the experiments for others, including French chemist Antonie Levoisier. After returning to Britain in January 1775, he continued his experiments and discovered vitriolic acid air (Sulphurdioxide, SO₂).
In March he wrote to several people regarding the new air that he had discovered in August. One of these letters was read aloud to the royal society, and a paper outlining the discovery, titled “An Account of further Discoveries in air”, was published in society’s journal “Philosophical Transactions”. Priestly called the new substance “dephlogisticated air” which he made in the famous experiment by focussing sun’s rays on a sample of mercuric oxide. He first tested it on mice, who surprised him by surviving quite a while entrapped with the air, and then on himself, writing that it was “five or six better than common air for the purpose of respiration, inflammation and I believe, every other use of common atmospherical air. He had discovered oxygen gas (O₂).”
Priestly called his discovery “dephlogisticated air” on the theory that it supported combustion so well because it had no phlogiston in it and hence could absorb maximum amount during burning.

Question 25.
Collect the information about annual fuel consumption in different parts of the world. How many years more the fossil fuels last? Make a poster with this information and issue an appeal to save fuel.
Answer:
Table showing different countries and their petrol consumption.

The information showing the remaining years in which fossil fuels exhausted.

We are using excess of petroleum products, coal and natural gas from the above table shows they will not exists long. So fuel consumption should be minimised otherwise no fuel is available in the future. So save fuel for better living.

8th Class Physical Science 8th Lesson Combustion, Fuels and Flame InText Questions and Answers

8th Class Physical Science Textbook Page No. 110

Question 1.
Why does candle give flame when it is burnt but why does coal burn without emitting a flame?
Answer:
A candle is made of wax in which a thick thread is inserted. When it is lighted melts by a match stick. A little of the wax forms gas. This gas combines with oxygen in the air to form flame.
But coal is a natural fuel contains more carbon. When it is burnt it sends out carbon monoxide and carbon dioxide gases and becomes ember and does not emit a flame. Coal is the changed material of wood. Hence it does not emit a flame as it possesses a huge calorific value (heat).

Question 2.
Do all fuels produce same amount of heat when they are burnt?
Answer:
No, different fuels produce different amount of heat when they are burnt.

Question 3.
What do we need to burn a material?
Answer:
We need oxygen to burn a material.

Question 4.
Have you ever tried burning a piece of paper or wood or coal, a small rock or a pebble?
Answer:
Yes, I tried.

Question 5.
Do all of them burn?
Answer:
Except a small rock and a pebble, the rest of them are burnt.

8th Class Physical Science Textbook Page No. 112

Question 6.
How does scented stick started burning?
Answer:
The stick starts burning with flame because oxygen supports combustion.

Question 7.
Why does not it catch again fire when it is kept aside in air after putting its flame off?
Answer:
The air is not sufficient to burn the scented stick.

8th Class Physical Science Textbook Page No. 113

Question 8.
a) A slow fire bursts into a flame when air is blown on it, but a candle burning with flame goes off when air is blown on it. Why?
Answer:
A slow fire burst into a flame when air is blown on it because it increase the supply of oxygen to fire. So combustion takes place to produce a flame.
Whereas when the wind or your breathe blows on the mixture of combustible particles and flame of a candle, it pushes the mixture of combustible particles away from the steam of fresh particles. So flame will be go out in the absence of combustible particles.

b) If a large quantity of dry grass is set on fire in forests then it is very difficult to put off the fire. Why?
Answer:
The dry grass is more combustible and supports burning. Hence due to the flow of oxygen (air) it is kindled.

Question 9.
When an object catches fire, the fire is put off by covering with sand or a blanket. Why ?
Answer:
Combustion takes place only in the presence of oxygen. When we cover a burning object with sand or blanket that would cut off the supply of oxygen to burning object. So the fire is puts off.

8th Class Physical Science Textbook Page No. 114

Question 10.
What makes match sticks to catch fire?
Answer:
A mixture of antimony trisulphide, potassium chlorate and white phosphorous with some glue and starch was applied on the head of a match stick made of suitable wood. When it struck against a rough surface white phosphorous got ignited due to heat of friction. This starts the combustion of match stick.

8th Class Physical Science Textbook Page No. 115

Question 11.
List different fuels that are used for!
Domestic purpose LPG, CNG
Automobiles/ Aircraft/ Trains/ Rockets Petrol, gasoline
Industry Coal, Charcoal, wood, natural gas
Classify the above fuels into solid, liquid, gases and write them in table.

Look at the fuels in the above table.

Classify the above fuels into solid, liquid, gases and write them in table.

a) Can you decide the best fuel among them?
Answer:
CNG, LPG.

b) What is the criteria to decide a best fuel?
Answer:
CNG & LPG burn completely. The fuel which burns completely is the best fuel.

8th Class Physical Science Textbook Page No. 116

Question 12.
What is calorific value? Write its units.
Answer:
Calorific value of a fuel is the amount of heat energy produced on complete combustion of 1 kg of that fuel.
It is measured in kJ/kg.

Question 13.
How can we put off the fire if it breaks out?
Answer:
We can put off the fire by using the fire extinguishers in which CO₂ gas is present.

Question 14.
How water helps in eliminating the factors, which support the combustion?
Answer:
The water spray cools the combustible material so that its temperature decreases. This prevents the fire from spreading.

Think and Discuss

8th Class Physical Science Textbook Page No. 111

Question 1.
Why some materials burn and why some do not? Give reasons.
Answer:
Burning is a process of reaction of a material with oxygen. The materials which have weak molecular bonds easily react with oxygen so they burn easily. The material which have strong molecular bonds does not react with oxygen easily because the molecular bonds should be broken before they react with oxygen.

Question 2.
Why some materials which do not burn at normal temperature burn at higher temperatures?
Answer:
Burning is a process of reaction of a material with oxygen. The material which have strong molecular bonds does not undergo burning because the molecular bonds should be broken in order to react the material with oxygen. So they have high ignition temperature. So the materials which do not burn at normal temperature burn at higher temperature.

8th Class Physical Science Textbook Page No. 112

Question 3.
If you lift the glass tumbler (which is placed over a burning candle) to 1 cm height what happens? Why?
Answer:
The Candle tends to burn because of availability air containing oxygen because cool air is more denser than hot air.

8th Class Physical Science Textbook Page No. 113

Question 4.
How do you say that the gas released in the above experiment is oxygen?
Answer:
If we put a burning match stick into the container having oxygen it burns with bright flame the reason is oxygen supports combustion.

Question 5.
Can we replace potassium permanganate with any other substance to release oxygen?
Answer:
We can replace with HgO (Mercuric oxide), KClO₃ (Potassium chlorate), H₂O₂ (Hydrogen peroxide), NaNO₃ (Sodium nitrate), KNO₃ (Potassium nitrate) for release of oxygen.

Question 6.
Is there any other procedure to prove that oxygen is needed for burning?
Answer:
We can put off a fire by covering with sand or blanket because we are preventing supply of oxygen. So we can say oxygen is needed for burning.

8th Class Physical Science Textbook Page No. 115

Question 7.
Why is phosphorous preserved in water? (Hint: Think about the role of ignition temperature in combustion)
Answer:
Phosphorous is highly reactive with air containing oxygen. It has low ignition temperature. So it catches fire at room temperature. So it is preserved in water.

Question 8.
Why kerosene stoves and Bunsen burners have small holes in them? (Hint: Think about the role of air in combustion)
Answer:
Kerosene stoves and bunsen burners have small holes for entry of air for combustion of fuel.

Question 9.
It is hard to ignite match stick in rainy days. Why?
Answer:
It is hard to ignite match stick in rainy days because water has extinguishing property.

8th Class Physical Science Textbook Page No. 118

Question 10.
A wax candle burns with a yellow flame. The domestic gas burns with a blue flame. Why?
Answer:
The wax candle burns with a yellow in the middle zone because it undergoes partial combustion whereas domestic gas burns with a blue flame because it undergoes complete combustion.

8th Class Physical Science 8th Lesson Combustion, Fuels and Flame Activities

Activity – 1

Question 1.
Do all materials bum?
You will need a pair of tongs, some metal or clay dishes and a candle or a spirit lamp. Using tongs, pick up a small piece of paper and bring it near to the lighted candle and keep it on flame as shown in figure.

Record your observations in table.


Carry out this experiment with a piece of charcoal, magnesium ribbon, straw, cotton cloth, nylon cloth, dry wood, pebble, wax, plastic piece, etc. and record your observations.
You can try to burn liquids like water, petrol, diesel, alcohol and note down your observations in table.
Take 2 ml of water in small plate. Bring the lighted stick near to water in plate.
a) What do you observe in your attempt of burning water?
Answer:
Water does not burn.

b) Is there any difference in flame of lighted stick?
Answer:
If we brought near to water plate the flame decreases.

c) What happened to the lighted stick when it is brought closer to water in the plate?
Answer:
The water in the plate puts off.the lighted stick.
Carryout this activity using coconut oil, mustard oil, kerosene, etc. Record your observation in the above table.

d) What can we conclude from this activity?
Answer:
We conclude that some materials burn and others do not.

e) Which of the material in the above activity are combustible?
Answer:
Except pebbles and water remaining materials are combustible.

Activity – 2

Question 2.
Testing the necessity of air for burning.
Answer:

Take a small burning candle and put it on a table. Invert a glass tumbler over it.
The candle continues to burn for some time. Then flickers and finally flame goes off.
Remove the tumbler and again light the candle. Put the tumbler back over the candle. When the candle flame begins to flicker, remove the tumbler. What happens to the candle?
We find that putting the glass tumbler over the candle cuts off the supply of air and candle flame goes off. When the flame just begins to flicker if we removes tumbler the flame retains back due to supply of oxygen.
This experiment proves that air is needed to burn a material.

Lab Activity

Write an activity to prove that oxygen helps in burning. (OR)
How can you perform the acitivity to prove that Oxygen is essential for burning? Explain.
Answer:
Aim: To prove that oxygen helps in burning.
Material required: Test tube, test tube holder, spirit lamp, match box, inscence stick (agarbatti), potassium permanganate (KMnO4) crystals.
Procedure:
Light a scented / incense stick and let it burn for 10 seconds, then put out the flame and keep it aside.
Take potassium permanganate (KMnO₄) in a test tube. Hold the test tube with a test tube holder and heat it over the flame of spirit lamp. Oxygen is released on heating of potassium permanganate (KMnO₄).
2 KMnO₄ → K2MnO₄ + MnO₂ + O₂ ↑
Insert the agarbatti with the burning stub into the test tube as shown in figure.

Observations: The stick burns with a flame. This proves that oxygen supports combustion by helping agarbatti to burn with bright flame.

Activity – 3

Question 3.
Burning a paper with sun rays.
On a sunny day, go out and focus the sun rays on a piece of paper using a magnifying lens.

a) Touch the spot after some time. How do you feel?
Answer:
It is hot.
You must have heard about people in ancient times rubbing the pieces of stones together to produce sparks.

b) Have you tried it?
Answer:
Yes.

c) Rub two stones together hardly and touch them. What do you feel?
Answer:
They become hot.
Now recall some of your experiences:

d) Does a matchstick burns by itself?
Answer:
No.

e) Why do you rub the match stick on the side of the matchbox to bum it?
Answer:
When we rub match stick on the side of the match box due to friction it produces it which will burn the match stick.

f) Can you bum a piece of wood by bringing it close to a lighted matchstick?
Answer:
No.

g) Why do we use paper pieces or kerosene oil to start fire in wood or coal?
Answer:
Paper or Kerosene oil has low ignition temperature. So they are used to burn wood or coal which have higher ignition temperature.

Activity – 4

Question 4.
Understanding ignition temperature.
Take two small paper cups. Pour water in one of the cups. Put the two cups on different tripod stands and heat both of them using a candle.

a) Which cup bums first?
Answer:
The cup which does not have water.

b) Does the water in the cup become hot? Why?
Answer:
The water in the second cup is hot because the heat received by second cup is transferred to water in it. The water in this cup prevents the paper to reach its ignition temperature and hence it does not burn.

c) When does the second cup start burning?
Answer:
When it reaches its ignition temperature.

Activity – 5

Question 5.
Observing the behaviour of different solid fuels.
Collect some fuels like candle, coal, charcoal, magnesium ribbon, wood, cakes of cow-dung, camphor, wick of the oil lamp, wick of kerosene stove, domestic gas, etc. Burn each of them one by one with the help of spirit lamp and note the time they take to catch fire. Also observe how do they burn?
a) Do all of them bum in the same manner? If not, what difference do you notice?
Answer:
No, some of them produce flame and some does not produce flame.

b) Do all of them form a flame while they are burning?
Answer:
No, all of them does not form flame.
Record your observation in the following table

You may observe that a candle burns with flame whereas charcoal does not. Some materials burn with flame, some do not. Kerosene oil and molten wax rise through the wick become gas and form flames. But charcoal cannot be vaporized. So it does not produce flame.

Activity – 6

Question 6.
Observing the structure of the flame.
Light a wax candle and watch the flame.

Carefully note the different coloured zones in the flame.
a) How many colours are there in the flame?
Answer:
There are three colours in the flame.

b) Starting from the base of the flame, how many flame zones do you observe?
What is the colour of the outer most zone of the flame?
Answer:
There are three flame zones are observed.
The colour of outermost zone is blue.

c) Observe the innermost zone which is dark. What do you observe there?
Answer:
In this zone wax gets vapourised. This is dark zone.
Observe near the base of the flame. Vaporized wax gets completely oxidized and burns with a blue flame. It is blue zone.

Activity – 7

Question 7.
Observing what happens in different zones of candle flame.
Light a candle. Hold a glass tube (with 7 cm length) a pair of tongs and introduce its one end in the dark zone of a non flickering candle flame. Keep lighted match stick near the other end of the glass tube as shown in the figure.

a) What do you observe? Do you see a flame? If so what is it, that produces a flame?
Answer:
Yes, the some of vapours produced by wax pass through the glass tube and are burnt by match stick to produce flame.

b) Notice that the wax near the heated wick melts quickly. What do you observe?
Answer:
When the candle’s flame is steady introduce a clean glass slide into the luminous zone of the flame and hold it with a pair of tongs for 10 seconds.
A blackish circular ring is formed on the glass slide.

c) What is it?
Answer:
The deposition of unburnt carbon particles present in the luminous zone of the flame due to incomplete combustion.

d) Hold a thin long copper wire just inside the flame for about half a minute. What do you observe? What is your inference?
Answer:
The copper wire just outside the flame gets red hot. It indicates that the non luminous zone of the flame has high temperature. It is the hottest part of the flame. It is blue in colour and complete combustion takes place due to good supply of oxygen.

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 6 Biodiversity and its Conservation

AP State Syllabus 8th Class Biology Important Questions 6th Lesson Biodiversity and its Conservation

8th Class Biology 6th Lesson Biodiversity and its Conservation 1 Mark Important Questions and Answers

Question 1.
What are Biosphere Reserves?
Answer:
Forests are Biosphere Reserves.

Question 2.
What is biodiversity?
Answer:
The variety and variability seen in plants and animals is called Biodiversity.

Question 3.
What are Endemic species?
Answer:
The plant or animal species of a particular area (zone), region or country is called endemic species.

Question 4.
What do you understand by Extinct?
Answer:
Species of plants and animals that have vanished from earth forever are called Extinct.

Question 5.
What do you understand the word Endangered?
Answer:
Plants and animal species that are on the verge of becoming extinct are called Endangered.

Question 6.
What is a Red Data Book?
Answer:
The book published by IUWC that contains the details of Endangered and Extinct species is called Red Data Book.

Question 7.
What do you see in National Parks?
Answer:
Conservation of wild life along with environment is seen in National Parks.

Question 8.
What is a sanctuary?
Answer:
A sanctuary is a place where conservation of wild life mostly birds takes place.

Question 9.
Give an example of a sanctuary.
Answer:
Krishna Sanctuary, Krishna & Guntur.

Question 10.
What is migration?
Answer:
Movement of birds for nestling from one region to another region is called migration.

Question 11.
Name the society for conservation of nature in London.
Answer:
International Union for Conservation of Nature and the Zoological Society of London.

Question 12.
Name the most threatened bird found in Palanadu Bird Sanctuary.
Answer:
Great Indian Bustard found in Pallanadu Bird Sanctuary.

Question 13.
Before 60 – 70 years what was the situation of the forests ofRampachodavaram?
Answer:
It was an abode for wild animals like tigers, leopards, deers etc.

Question 14.
What is the present situation of the forests ofRampachodavaram?
Answer:
Forest area was cleared and so several organisms started disappearing.

Question 15.
Why should we conserve a small insect like a bee or a butterfly?
Answer:
Most of the flowers get pollinated through bees and butterflies. So they should be conserved.

Question 16.
Why is the number of butterflies decreasing?
Answer:
The insects are decreasing due to spraying of pesticides and insecticides on crop plants.

Question 17.
How can ‘project tiger’ help to save wild life?
Answer:
This project helped to increase the number of tigers and to save tiger from the brink of extinction.

Question 18.
How is the project tiger achieved?
Answer:
The success of the project was achieved by enforcement of strict anti poaching measures and scientific conservation practices.

Question 19.
While saving tiger, why should it’s food web also be protected?
Answer:
The tiger depends for food on the deer and many other herbivores. If the tiger disappears, the deer and other herbivores will increase and that would affect the flora of the area.

8th Class Biology 6th Lesson Biodiversity and its Conservation 2 Marks Important Questions and Answers

Question 1.
What are the conservation methods do you suggest to protect the most threatened species?
Answer:

1. Taking measures to protect their natural habitats.
2. Creating awareness at community levels.
3. Strict implementation of National Wild life Protection Act, would help these species.
4. Prohibition of human activities in their habitats.

Question 2.
What are endemic species? Give some examples.
Answer:
Plants or animal species found restricted to a particular area of a country are called Endemic Species.
Ex: Broad tailed Grass bird, Peacock, Malabar Parakeet, Black Buck etc.

8th Class Biology 6th Lesson Biodiversity and its Conservation 4 Marks Important Questions and Answers

Question 1.
Collect the pictures of the following endangered species of plants and animals and paste them in your scrap book and write their names below the pictures.
Answer:

Question 2.
How do we depend on forests?
Answer:

1. Forests play a key role in maintenance of ecological balance.
2. Forests absorbs a large amount of Carbondioxide and Particulate Matter (CPM) and keep the air clean. They serve as lungs of our earth.
3. Forests are the natural sources of a variety of timber yielding plants and forests products like cane, resins, lac, fruits, nuts and honey.
4. Forests provide us with cool breeze which helps in the rainfall.
5. They are the natural habitats for wild animals they serve as biosphere reserves.

Question 3.
What steps do you take to stop deforestation?
Answer:

1. We should stop cutting of forests for farming and industrial purpose.
2. Planting trees like Tamarind, Amla, Tangedu, Subabul, Bamboo in rural areas.
3. Measures should be taken to conserve soil moisture by constructing checkdams and bundhs.
4. Measures should be taken to improve forest productivity by planting fruit and nut bearing plants.
5. Measures should be taken reforestation in order to maintain sustainability of forests.

8th Class Biology 6th Lesson Biodiversity and its Conservation Important Questions and Answers

Question 1.
List any four medicinal plants and their uses.
Answer:
The following are the some of the medicinal plants of our area and their use.

1. Neem – Antiseptic
2. Garlic – Used for lowering cholestrol and blood pressure.
3. Ginger – Used to ease nausea and motion sickness.
4. Feverfew – Used to treat fevers.

Question 2.
Match the following and answer the following question.
1) Endangered species              a) Hyderabad Pigeon
2) Endemic species                    b) Dinosaur
3) Invasive species                     c) Kiwi
4) Extinct species                       d) Spotted chital deer
e) Crow
Answer:
1 – d
2 – c
3 – a
4 – b
Question.
What is a Red Data Book?
Answer:
The book published by IUWC that contains the details of Endangered and Extinct species is called Red Data Book.

Question 3.
What is migration? Give some examples for migratory birds.
Answer:

1. Moving of birds in flocks from one region to another for getting shelter and food is called as “migration”.
2. Examples for migrating birds are great spotted wood pecker, coaltit, pelicon, black – tailed godwits, plover, etc.

Question 4.
Read the following paragraph.
Sometimes at night we see birds flying in groups. These birds which do not have permanent nestlings and join into small flocks and move from one region to other for food and shelter called as ‘Migration’ and such birds are called Migratory birds. During the rainy season most of the birds from far away places migrate to Kolleru and Pulicat lakes of our state. They build their nests on the trees in the nearby villages. Due to the cut down of trees, less number of birds are coming to here.
Answer the following questions.
a) What are Migratory birds ? Why do they migrate one place to another?
b) What are the reasons for less number of birds migrating to India?
Answer:
a) The birds which are moving in flocks from one region to other for food and shelter are called “migrating birds”.
b) Due to cutting down of trees in the villages near the lakes, birds are facing scarcity of their nesting habitats.

Question 5.
What measures are to be taken to save paper?
Answer:

1. We should always use recycled paper.
2. Use paper only if we need.
3. We should use electronic transfer methods for our daily transactions.
   Ex: Paying of electricity bills, filling of online application but not paper application.

Question 6.
Study the following para and answer the questions.
Did you get the same number and types of birds every day ? Was there any sudden variation in a particular season ? Did you notice any new type of bird population in any season ? Discuss with your friends about the effect of the presence of such a population. Why do these birds move from one place to another ? Sometimes at night we see birds flying in groups. Where do they fly? Think. Sometimes some birds live in the same habitat throughout the year. Other birds which don’t have permanent nestlings and join into small flocks and move from one region to the other for food and shelter (nesting habits) called as ‘Migration’ and such birds are called as ‘migratory birds ’. During rainy season most of the birds from far away places migrate to Kolleru and Pulicat lakes of our State. They build their nests on the trees in the nearby villages also. In the olden days people believed that these migrated birds are divine ones. But nowadays most of the trees are getting cut down. There is hardly any place for birds to build their nests.
a) What does the above information says?
b) What you say the birds come to our places from distant places?
c) What should we do for the birds to migrate to our place?
d) Name some migratory birds.
Answer:
a) Affects of deforestation on bird migration in Kolleru.
(Or)
Loss of bird habitats due to cutting down of trees in Kolleru.
b) Bird migration.
c) 1) Avoid cutting of trees in lake areas strictly.
2) We should strictly monitor the increased human activities in all lake areas.
d) Great spotted wood pecker, pelicans, coaltit, Siberian cranes.

Question 7.
What are the effects of deforestation?
Answer:

1. Change in rainfall pattern.
2. Increase in green house gases.
3. Loss of wild life habitats.
4. Increase in soil erosion.
5. Massive floods.
6. Global warming.
7. Droughts.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 2 Friction Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 2nd Lesson Friction

8th Class Physical Science 2nd Lesson Friction Textbook Questions and Answers

Improve Your Learning

Question 1.
Do you agree with the statement, “friction is both good and an evil”? Explain with examples.
Answer:
Yes, I agree with the statement friction is both good and an evil.
Explanation with examples.
a) Friction is good:

1. We cannot walk or run without friction.
2. We will not have any cars or bicycles because all of them move because of friction.
3. We cannot stop a moving car by applying brakes.
4. Carpenters will not be able to smoothen surfaces.
5. We will not able to hold any appliances such as hammer, soap, etc.
6. It will not possible to write with pen or pencil if there is no friction.
7. We could not fix nail on the wall.
8. No building could be constructed if there is no friction.

b) Friction is an evil: Friction is undesirable in machinery because it is responsible for overheating and wearing out of moving parts.

Question 2.
Explain why sportsmen use shoes with spikes.
Answer:
The spikes will increases the frictional force so that the sportsmen will get better grip on the floor.

Question 3.
Would it be easier or more difficult for you to walk on soapy water on the marble floor ? Why ?
Answer:
It is more difficult to walk on a marble floor having soapy water because soapy water acts as lubricant and decreases the friction.

Question 4.
What ways do you suggest to reduce friction?
Answer:
Ways of reducing friction:
a) Polishing: Decreasing irregularities of surface (or) smoothening the surface.
B) Lubricants: Using lubricants which will decrease the friction.
c) Ball bearings: Using ball bearings in machinery.
d) Steam lining: Automobiles and aeroplanes are steam lined to reduce the friction due to air.

Question 5.
What conditions are needed for static friction to come into play?
Answer:
The object should be at rest with respect to the surface upto certain limiting acceleration.

Question 6.
Give examples of practical application of static friction.
Answer:
The objects unable to move on their own is due to static friction between surfaces of object.
The practical application of static friction:

1. Construction of buildings.
2. Fixing nail in the wall.
3. A book placed in the shelf unable to change its position because it is unable to overcome frictional force.
4. We can write with pen or pencil due to static friction between finger and pen or pencil.
5. We will not able to hold appliances such as hammer.

Question 7.
Give examples showing the existence of sliding friction.
Answer:

1. A moving ball stops after sometime.
2. If we push an object it will stop after sometime.

Question 8.
Explain how can you measure frictional force?
Answer:
Tie a string around a brick. Pull the brick by a spring balance. When the brick just begins to move note down the reading on the spring balance that measure the force of friction between the surface of brick and the floor.

Question 9.
Explain how does lubrication reduce friction?
Answer:
When oil, grease or any other lubricants are applied between the moving parts of a machine, a thin layer formed between the moving surfaces so they do not directly rub against each other which will avoid the interlocking of irregularities. So lubrication reduce the friction.

Question 10.
What kinds of friction do you know?
Answer:
There are three types of friction.

1. Static friction
2. Sliding friction
3. Rolling friction

Question 11.
Explain why sliding friction is less than static friction.
Answer:
When an object starts sliding, the contact points on its surface do not get enough time to lock into the contact points on the floor. So the sliding friction is slightly less than the static friction.

Question 12.
Give examples of how is friction responsible for energy wastages? Give suggestions to reduce energy wastages by friction.
(OR)
How is friction responsible for energy loses give examples? Give suggestions to reduce energy loses by friction.
Answer:
As the friction increases the machinery parts develops heat there by efficiency of the machine decreases which leads lot of wastage of energy. The wastage of energy is due to overheating and wearing out of moving parts.
Suggestions:

1. To reduce friction between rotating shafts of machine tools we should have to use ball bearings.
2. Replacing wearing out of moving parts with new ones.

Question 13.
Seetha is observing a moving bus with the luggage on its top. As the bus is moving slowly there is change in the state of luggage on its top. But when the bus speeds up and starts moving fast, she noticed that the luggage on the top of the bus fell to the back of the bus. This raised many doubts in her mind regarding to the effect frictional force acting on the luggage as well as on the tyres of the bus. Can you guess the questions raised in her mind ? Write them.
Answer:

1. Why the bag is moving backward direction?
2. In which direction friction is acting on the bus as well as on the bag?
3. Whether frictional force effecting relative motion between bag and bus?
4. What happens to frictional force if we replace bag with other object?

Question 14.
Collect information either from internet or from books in library, about various new techniques being adopted by human beings to reduce energy losses due to friction. Prepare a note on that.
Answer:

1. We are using grease, oil, wax and other lubricants in the vehicles and machinery to reduce the friction.
2. Ball bearings are also used to reduce the friction.
3. Engine oil, gear oil, brake oil, clutch oil, etc. are used in vehicles.
4. Shock up oil is also used.
5. Levers are reducing the friction.
6. In trolleys and other vehicles which should carry heavy loads, the wheels are fixed.

Question 15.
Draw a free body diagram (FBD) to show various forces acting on a body which is sliding on an inclined plane.
Answer:

Question 16.
“Reducing friction to the lowest possible level in machine tools solves the problem of energy crisis and conserve biodiversity”. How do you support the statement? Explain.
Answer:
Yes, it will solve the problem of energy crisis and conserve biodiversity the reason is the majority of energy wasted in the form of heat energy due to friction. In order to develop more electrical energy we are depending on coal, petroleum, gas, nuclear energy and hydro electricity. The production of energy from these sources except hydroelectric power causing severe air pollution which are affecting animals and plants. So energy should be conserved by means of reducing friction.

8th Class Physical Science 2nd Lesson Friction InText Questions and Answers

Think and Discuss

8th Class Physical Science Textbook Page No. 22

Question 1.
Does friction oppose motion or relative motion of surfaces in contact? Discuss.
Answer:
Yes. Frictional force opposition or relative motion of surfaces in contact that’s why an object placed on a table unable to move on its own because it is unable to overcome friction similarly a moving ball comes to rest after sometime due to friction.

Question 2.
What observations and experiments can you cite to show the existence of friction?
Answer:

1. Push a ball on a sandy surface and on a concrete surface and the observation is on a concrete surface it travels more distance, the reason is the concrete surface apply less frictional force on the ball.
2. Apply vehicle brakes during summer and rainy seasons and the observation is during summer season the brakes works more efficiently than rainy season the reason is friction between tyre and brakes is less because rainy water acts as lubricant.

Question 3.
When do we speak of sliding friction?
Answer:
When applied force is more than the limit of static friction, the body starts to move then we speak about sliding friction.

8th Class Physical Science Textbook Page No. 25

Question 4.
Does friction act on a table resting on the floor?
Answer:
Yes, frictional force is acting on the table which is known as static friction.

Question 5.
If normal force is doubled ? What happens to friction? Discuss.
Answer:
Friction is directly proportional to normal force therefore friction will be doubled if the normal force is doubled.

Question 6.
Your friend says “friction depends on the area of contact?” How do you correct your friend through some experiments ?
Answer:
If is plain that the friction doesn’t depend on area of contact, I will explain this fact to my friend by fastening a brick kept horizontal to the surface to a spring balance and pulling it at the hook. The same experiment I do by keeping the brick vertical to the surface. In both the experiments we find no difference and I will make him to come to the conclusion that the friction depends on the normal force and not on weight of the object on the surface of contact.

Question 7.
“Friction is independent of weight, but depends on normal force between surfaces of contact where friction exists.” Do you agree with this statement? Discuss.
Answer:
Yes, I agree with this statement. The above experiment helps us to come to this conclusion. In both cases we used the same brick hence the weight doesn’t change. But when its positions were changed the frictions at each case is changed.

8th Class Physical Science Textbook Page No. 26

Question 8.
What important role does friction play in the life of human beings and animals?
Answer:

1. Without friction human beings and animals unable to walk or run on any surface.
2. Without friction they unable to hold any appliances.
3. It will not be possible to write with pen or pencil if there is no friction.
4. We cannot stop car or cycle by applying brakes.
5. No building is constructed if there is no friction.
6. Carpenters will not be able to smoothen surfaces.

Question 9.
Why is friction important for transport?
Answer:
Threading in tyres provide friction for cars or buses so that they can move safely therefore friction is important for transport.

8th Class Physical Science Textbook Page No. 28

Question 10.
Can we reduce friction to zero? Explain.
Answer:
No, we cannot. Friction can never be entirely eliminated because no surface is perfectly smooth and some irregularities are always there.

Question 11.
What purposes are served by bearings in machines? Explain with daily life situations.
Answer:
The ball bearings are used to reduce friction between rotating shafts of machine tools and it increases the efficiency of machines.

8th Class Physical Science 2nd Lesson Friction Activities

Activity – 1
Question 1.
Identifying forces acting on a body and effect of frictional force.
Gently push a book on a horizontal floor. You may observe that the book acquires certain speed in the direction of push. However, the speed of the book gradually decreases and after sometime it stops.

a) Why does the book stop after covering some distance?
Answer:
Some opposing force is acting to its motion.

b) Is the book moving with uniform speed?
Answer:
No, its speed decreases gradually.

c) Why does the speed of the book change gradually?
Answer:
Some net force is acting opposite direction to its motion.

d) How many forces act on the book when it is pushed on the floor?
Answer:
Two forces act on the vertical direction. They are

1. Weight of the book or gravitational force acting vertically down.
2. Normal force or reaction force applied by the floor vertically up.
3. Forces acting horizontal direction.

e) What are the forces acting on the book in the horizontal direction?
Answer:

1. Muscular force applied by us.
2. Opposing force acting opposite to motion of book.

f) What is the net force acting in the horizontal direction?
Answer:
The net force is the difference between muscular force and opposing force to the motion of book.

Lab Activity

Write an activity to understand friction and static friction.
(OR)
Conduct an experiment to understand the nature of friction and the concept of static friction.
Answer:
Aim: To understand the nature of friction and the concept of static friction.
Materials required: Toy trolley, small wooden block, inextensible string, weight hanger, weights, pulley and table.
Procedure: Take a small toy trolley and keep a small wooden block on it as in the figure. Tie an inextensible string to the trolley and pass it over a pulley. And other end of the string is fixed to weight hanger. Take a small weight and keep it on weight hanger and observe the changes in motions of block and trolley.

Observation:
The trolley with block moves towards left with an acceleration. The block is not with respect to the surface of trolley, but it is in motion with respect to surface e table. The force of friction of the trolley acts on the direction of motion.
We increase trolley’s acceleration gradually by increasing the weight on the hanger at certain limiting weight the block comes in motion in the reverse direction.
That means now there exists relative motion between the surface of the trolley and block.
Result:
The force which opposes the relative motion of the two surfaces of bodies which are in contact is called frictional force.
The block is at rest relative to surface of the trolley upto a certain limiting acceleration. The friction exists at that stage is called static friction.

Activity – 2

Question 2.
Observing the variation of friction.
Push a heavy box which is kept on a floor. The box does not move. Now increase the applied force until the box moves.

a) Why does the box does not move at first?
Answer:
The applied force is less than frictional force (static friction).

b) When does the box tends to move?
Answer:
When the applied force is more than static friction.

Activity – 3

Question 3.
Effect of roughness on frictional force.
Set up an inclined plane on the horizontal floor. Use a wooden board as inclined plane. Put a mark at any point
‘A’. Now let a pencil cell or ball is move down from this point. Note down the distance travelled by the ball from the bottom of the inclined plane to point where it comes to a stop.

Now, spread a cloth over the floor. Try again with ball and note down the distance.

a) What are your observations from these experiments?
Answer:
The distance covered by ball in the two cases are different.

b) In which case is the distance covered maximum?
Answer:
When there is no cloth on the floor.

c) In which case is the distance covered minimum?
Answer:
When cloth is spread over the floor.

d) Why is the distance covered by the pencil cell different on different surfaces?
Answer:
Because, the friction offered by different surfaces are different.

e) If the cloth is replaced with white marble surface or glass surface, what will be your prediction about the distance covered by the pencil cell?
Answer:
The pencil cell covers more distance.

Activity – 4

Question 4.
Effect of area of contact on frictional force.
Tie a string around a wooden block and pull the wooden block by using a spring balance.

Pull it to make a move in the brick. Note down the readings of spring balance when the brick just begins to move.
a) How many forces are acting on the wooden block in the horizontal direction?
Answer:
Two forces are acting in the horizontal direction.

1. Force of friction,
2. Force applied by us.

Now turn the wooden block upright and measure the friction by doing the same experiment using the reading of the spring balance.

b) How does the frictional force vary with the change in the area of contact?
Answer:

The frictional force appears the same in both cases irrespective of area of contact. So it is independent of area of contact.

Activity – 5

Question 5.
Effect of normal force on friction.
Keep a wooden block on the horizontal floor and pull it with the spring balance attached to it and measure the frictional force.
Now put another wooden block over the brick tied to the spring balance or press it vertically with your hand and measure the frictional force.
a) Is there any difference between frictional forces in two cases? If yes, why?
Answer:
Yes, the reason is when we add a wooden block to the existing wooden block or apply force by pressing vertically, the normal force increases and hence we find increase in frictional force.

b) What is the relationship between friction and normal force?
Answer:
Friction is proportional to the normal force, i.e., friction °c normal force.

Activity – 6

Question 6.
Friction produces heat.
a) Rub your palms against each other for a few minutes. How do you feel?
Answer:

They became hot.

b) Strike a match stick against the rough surface of match box. What happens?
Answer:
The match stick catches fire.

c) What is your observation in this activity?
Answer:
Temperature of surfaces increases due to friction.

d) What is your conclusion on this activity?
Answer:
Friction can also produce heat.

e) You have probably heard that space craft returning to the earth have to be protected by a heat shield covering it. Find out why. What is the material used as heat shield?
Answer:

Space craft returning earth have to be protected by a heat shield covering it in order to protect it from atmospheric friction.
The material generally used is insulator of heat.

Activity – 7

Question 7.
How to increase Motion?
Take a spoon and hold its head (broader portion) in the left hand and hold the mid portion of the spoon by the right hand and pull it towards the other end of the spoon.
a) What do you notice?
Answer:
We unable to pull the spoon.
Now dip your right hand fingers in water, do it again as said above.

b) In which case is it easy to pull? Why?
Answer:
In second case it is easy to pull because water decreases the friction.

c) Have you ever thought why the sole of your shoes is grooved as shown in figure?
Answer:

It will provide shoes better grip on the floor so that we can move safely.

d) Cars, trucks and bulldozers tyres are threaded. Why?
Answer:

To provide them better grip on the floor.

e) Why do you need to change the tyres when it’s threading is worn out?
Answer:
If we does not change the tyre then the frictional force decreases and the vehicle may skid.
Play carrom board without powder and then play with fine powder sprinkled on board.

f) In which case is the movement of the striker and the coins easy? Why?
Answer:
When fine powder sprinkled on board, it will decrease the friction between coin and board surface.

g) Why do we pour a few drops of oil on the hinges of a door?
Answer:
It will decrease the friction and provide better movement of door.

h) Why do we use grease between the moving parts of motor vehicles?
Answer:
To reduce friction in order to increase efficiency.

Activity – 8

Question 8.
Effect of rollers on friction.
Pull a suitcase without rollers and pull a suitcase which has rollers.

a) In which case is the pulling easy? Why?
Answer:
It is easy to pull when suitcase has rollers.
Try to push a book lying on the table. Now place the book on two to three pencils or pens without caps. Push the book again.

b) What do you notice ? In which case is it easy to pull the book? Why?
Answer:

In the second case it is easy to pull the book. The reason is it is always easier to roll a body than to slide it over a surface.

Activity – 9

Question 9.
Understanding the principle of ball bearings.
Take two lids and rotate them by putting one on the top of the other.

a) What do you observe?
Answer:
It is difficult to rotate them.
Now place three to four marbles on one lid and place the other lid on the top of the marble. Now try to rotate the top lid.

b) What do you observe?
Answer:
Now we can easily rotate the lid because rolling friction is less than sliding friction.

c) What is your conclusion on the principle of ball bearings?
Answer:
We can easily rotate top lid by placing marbles between the lids. This is the principle of ball bearings.

Activity – 10

Question 10.
Observing fluid friction.
Take a glass of water and stir it with a spoon. You know that water whirls around an axis. Stop stirring and see what happens.

The whirling speed of water gradually decreases and after some – time, the water stops whirling and comes to a stable state

a) Which force is responsible for stopping the rotation of the water.
Answer:
The frictional forces between the liquid layers or between the liquid surfaces that is in contact with glass surface.

Activity – 11

Question 11.
Identifying factors influencing the fluid friction.
Take a tub of water. Try to move your hand in water in the direction of stretched fingers i.e., up and down. Now try to move your hand in the direction perpendicular to the plane of the hand i.e., to and fro.

a) In which orientation of your hand, do you experience more drag? Why?
Answer:
We experience more drag in the direction of stretched fingers. The frictional force on an object in a fluid depends on its speed with respect to fluid and on the shape of the object and nature of the fluid.
When objects move through fluids, they have to overcome friction acting on them. So objects are given special shapes to minimise fluid friction.

b) Where do you think scientists get hint for these special shapes?
Answer:
From nature i.e., from birds and fishes, which have to move about in fluids all the time.

c) Do you find any similarity in the shape of an aeroplane and a bird? Why?
Answer:
Yes. The shape of aeroplane designed as bird in order to reduce fluid friction.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 3 Matter Around Us

AP State Syllabus 8th Class Physical Science Important Questions 3rd Lesson Matter Around Us

8th Class Physical Science 3rd Lesson Matter Around Us 1 Mark Important Questions and Answers

Question 1.
What is CNG?
Answer:
CNG means Compressed Natural Gas.

Question 2.
Does the smoke of incense stick diffuse in a room without air?
Answer:
Smoke of incense stick is a gas. Gas diffuses in air only. So the smoke cannot diffuse in the absense of air.

Question 3.
Write decreasing order of the distance between the atoms of solid, liquid and gas.
Answer:
Gas > Liquid > Solid.

Question 4.
What is the temperature where water expands?
Answer:
When temperature is reduced from 4°C to 0°C, water expands instead of compression.

Question 5.
What is dry ice?
Answer:
Solid carbon dioxide is called dry ice.

Question 6.
What is Kelvin scale equivalent to 0°C?
Answer:
273 K.

Question 7.
What are the factors influencing the change in state of a matter?
Answer:

1. Temperature
2. Pressure.

Question 8.
What is humidity?
Answer:
The amount of water vapour present in air is known as humidity.

Question 9.
What is meant by sublimation?
Answer:
When a substance is heated its state changes from solid to vapour directly without changing into liquid. This is called sublimation.

Question 10.
How do acquatic animals and plants survive under water?
Answer:
The gases like oxygen and carbon dioxide will diffuse in water. The acquatic animals under water will survive by inhaling these gases.

Question 11.
What are the different states of matter?
Answer:
Matter exists in three states. They are solids, liquids and gases.

Question 12.
Why are the liquids called fluids?
Answer: Liquids can flow easily from one container to another. Hence they are called fluids.

Question 13.
Why is the solid carbon dioxide called dry ice?
Answer:

1. Solid carbon dioxide converts directly into gaseous state when the pressure is decreased to 1 atmosphere.
2. Due to this reason solid carbon dioxide is also known as dry ice.

Question 14.
Why is the rate of diffusion in gases high?
Answer:
The rate of diffusion in gases is very high than liquids and gases, because

1. Higher speed of gas particles.
2. Greater space between the particles of gas.

Question 15.
Which will decide the change of state of substance?
Answer:
Pressure and temperature decides the state of the substance.

Question 16.
What is the principle involved in ice skating?
Answer:
Pressure is applied on ice with skating boots. As the pressure increases melting point ice decreases. So ice melts at a lower temperature than 0°C. Therefore skating is possible on ice.

Question 17.
What is compression?
Answer:
The volume of gas can be decreased by applying pressure. This process is called compression.

Question 18.
What are fluids?
Answer:
The substances which can flow from one place to other place are called fluids. Generally liquids and gases are fluids.

8th Class Physical Science 3rd Lesson Matter Around Us 2 Marks Important Questions and Answers

Question 1.
What is matter? Give some examples from your day-to-day life.
Answer:
Anything in this world that occupies space and has mass is considered as matter. Examples:
The water we drink, our food, clothes, chairs, tables, air we breath, etc. are the examples of matter.

Question 2.
Compare the following properties of solids, liquids and gases,
a) Shape b) Volume c) Compressibility d) diffusion
Answer:

Question 3.
Give the order of rate of diffusion in solids, liquids and gases.
Answer:
The order of rate of diffusion in solids, liquids and gases is
Gases > Liquids > Solids (or) Solids < Liquids < Gases

Question 4.
Give some experiences with evaporation in your daily life.
Answer:

1. We feel cooler after sweating.
2. Drying of wet clothes when exposed to the sun.
3. Paddy, cereals, etc. will be exposed to the sun to remove moist.
4. Water stored in earthen pots is cooler than the water stored in a metal pot.
5. Fog, which is formed early in the morning during winter season will disappear after sunrise.

Question 5.
Why do we feel cool when nail polish is applied to nails?
Answer:
Nail polish contains acetone which absorb heat energy from our body and evaporates. So the body temperature decreases. So we feel cool when nail polish applied to nails.

Question 6.
Why do we store water in earthen pots?
Answer:
The earthen pots have small pores in it. From that pores water tends to evaporates by gaining heat energy from the pot. So water in pots is cool. So water is stored in earthen pots.

Question 7.
Why do clothes dry faster on a sunny and windy day compared to rainy season ?
Answer:
If the amount of water vapour is high in air the rate of evaporation will decrease. So clothes dry slowly during rainy season but fast on a sunny and windy day.

Question 8.
Why do we require pressure cookers at higher altitudes?
Answer:
At higher altitudes the atmospheric pressure decreases. So the boiling point of water decreases. So, the heat energy supplied is not sufficient to cook food. Therefore we require a pressure cooker to increase the pressure. Thus the boiling point of water inside the cooker increases to 120°C and heat energy is sufficient to cook food.

Question 9.
Two pieces of cotton rolls one is soaked in ‘A’ chemical, and other one is soaked in ‘B’ chemical are inserted in a glass tube as shown in the figure.

a) If ‘A’ is HCl, what would be ‘B’?
b) In which state the rate of diffusion is high?
Answer:
a) If ‘A’ is HCl, then ‘B’ should be Ammonium solution. Because it formed Ammonium chloride.
b) Rate of diffusion is high to ‘B’ than ‘A’.
Because the product Ammonium chloride formed nearer to ‘A’ chemical.

Question 10.
One part of the substance was boiled in water at 100°C. Other part of the substance was boiled in water vapour at 100°C.
a) Which one would be boiled fast?
b) Guess the reason.
Answer:
a) Substance boiled in water vapour at 100°C is boiled fast.
b) Particles in water vapour at 100°C have more energy than the particles in liquid water at the same temperature. This is because of particles in water vapour have absorbed additional energy in the form of heat of vaporization.

Question 11.
Balaraju hanged his washed clothes under fan which is rotating.
Venu Gopal hanged his washed clothes under shadow.
a) Which one dries early? Why?
b) Write the name of the process that involved in drying.
Answer:
a) The clothes hanged by the Balaraju were dried faster, because, evaporation increases with wind speed.
Due to increase of wind speed, water vapour particles move away with the wind, decreasing the amount of water vapour in the surroundings.
b) The process involved in drying up the clothes is evaporation.

Question 12.
Observe the given graph and answer the following :

1. What is the melting point in the graph?
2. What is the boiling point in the graph?
3. Guess the substance.
4. What is the maximum temperature that hold the substance?

Answer:

1. The melting point is 0°C.
2. The boiling point is 100°C.
3. The substance should be water.
4. We can rise the temperature of the substance upto 100°C.
   The maximum temperature that hold by the water is 100°C.

8th Class Physical Science 3rd Lesson Matter Around Us 4 Marks Important Questions and Answers

Question 1.
How can you prove that the solids have definite shape and a fixed volume ?
Answer:

1. Take two solid objects, say a pen and a book.
2. Put them in different containers.
3. We observe that there is no change in their shape or volume.
4. Drop a book on the floor.
5. If will not flow like a liquid, but remain rigid.
6. These activities prove that solids have definite shape and a fixed volume.

Question 2.
What are the general properties of matter ?
Answer:
The general properties of matter:

1. Matter is made up of tiny particles. Their size is beyond our imagination.
2. Matter exists in three states i.e. solid, liquid and gas.
3. There exists space between the particles of matter.
4. There exists some force of attraction between the particles of matter.
5. Matter can change its state from solid to liquid, liquid to gas and vice versa, by changing temperature and pressure.
6. Matter has the properties of compressibility and diffusion.
7. Particles of matter move continuously in liquids and gases.

Question 3.
Define: a) Latent heat b) Latent heat of fusion c) Latent heat of vaporisation.
Answer:
a) Latent heat: The amount of heat energy that is required to overcome the attraction
energy among the particles is given by the latent heat of the substance.
b) Latent heat of fusion: Latent heat of fusion is defined as the amount of heat energy required to change 1 kg of a solid, completely into liquid at atmospheric pressure at its melting point.
c) Latent heat of vaporisation : Latent heat of vaporisation is defined as the amount of heat energy required to change 1 / of a liquid, completely into vapour at atmospheric pressure at its boiling point.

Question 4.
How is marine life possible in extremely cold areas ?
Answer:

1. The volume of water between 0°C to 4°C shrinks.
2. Same amount of water in solid ice occupies more volume than liquid water.
3. So ice floats on water rather than shrinking.
4. In extremely cold weather, the water at the top becomes colder and colder, until it freezes.
5. While the ice floats on the top, the animals continue to live in the water below, which does not freeze and remains at 4°C.
6. The ice on the top of the pond insulates the water, below it as it stops the water from losing the heat to air.
7. This is very important for survival of marine life which lives in ponds in the colder areas.

Question 5.
How does diffusion helps to survive the animals and plants in daily life ?
Answer:

1. It is clear that solids and liquids diffuses into liquids and gases diffuses into gases.
2. Certain gases from atmosphere particularly oxygen and carbon dioxide diffuse and dissolve in water and support the survival of aquatic animals and plants.
3. Diffusion therefore is a very important process for living things.
4. During respiration oxygen diffuses from lungs into blood. Carbon dioxide diffuses from blood into lungs.

Question 6.
How do you appreciate the process of diffusion ?
Answer:

1. Diffusion is a very important process for living things.
2. Oxygen diffuses into air and available for every human beings and animals.
3. CO₂ diffuses into air and available to plants.
4. Oxygen and CO₂ diffuse and disolve in water and support the survival of aquatic animals and plants.
5. During respiration oxygen diffuses from lungs into blood.
6. Smell of flowers, scents diffuses and reaches to our nose to give happiness to us.
7. We can recognise leaking of L.P. Gas in our house by diffusion process.
8. Diffusion of sugar and salt, give taste to drinks.
9. In this way diffusion is useful in our daily life.
   So, I am appreciating the process of diffusion.

Question 7.
How do you appreciate the process of evaporation ?
Answer:

1. The process of change of a liquid into vapours at any temperature below its boiling point is called “evaporation”.
2. It is very useful in our daily life.
3. Drying of wet clothes in air is the result of evaporation.
4. Drying of sweat from the human body and giving cooling is also result of evaporation.
5. After washing the floors, dishes evaporation takes place and dries up.
6. Water cools when it store in matkas (earthen pots). Evaporation process involved in it.
7. Water evaporate from the sea and forms clouds to rain.
8. In this way evaporation process is helpful to us.
9. So, I am appreciating it.

Question 8.
Find out the process involved in given situations.

Answer:
a) evaporation
b) melting
c) evaporation
d) diffusion
e) diffusion
f) boiling
g) diffusion
h) evaporation

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 7 Coal and Petroleum

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

8th Class Physical Science 7th Lesson Coal and Petroleum 1 Mark Important Questions and Answers

Question 1.
What are exhaustible resources? Give examples.
Answer:
The resources which are limited in nature and can be exhausted by human activities are called exhaustible resources, e.g. Coal, petroleum and natural gas.

Question 2.
What are inexhaustible resources? Give examples.
Answer:
The resources which are unlimited in nature and not likely to be exhausted by human activities are called inexhaustible resources, e.g. Solar energy, wind energy, tidal energy.

Question 3.
When and where does petroleum first used?
Answer:
More than 4000 years ago, asphalt (petroleum product) was used in the construction of walls and towers of Babylon. There are also records from ancient China about shallow wells being dug to get petroleum.

Question 4.
What did our ancestors do with petroleum?
Answer:
They mainly used petroleum for their wooden boats and waterproof, as a fuel for lamps and in some traditional remedies.

Question 5.
What is the basic difference between coal and charcoal?
Answer:
Coal used in factories is mined from the earth’s crust. The charcoal is obtained from firewood.

Question 6.
What is meant by fractional distillation?
Answer:
The separation technique used to separate various components of petroleum is called fractional distillation.

Question 7.
What is carbonisation?
Answer:
The slow process of conversion of dead vegetation into coal is called carbonisation.

Question 8.
Why coal, petroleum and natural gas are called fossil fuels?
Answer:
They were formed from the dead remains of living organisms (fossils). So these are called fossil fuels.

Question 9.
What is coke and what are its uses?
Answer:
Coke is a tough, porous and black substance. It is an almost pure form of carbon. Uses:

1. Coke is used in the manufacture of steel.
2. In the extraction of many metals.

Question 10.
Why petroleum is called black gold?
Answer:
Due to its great commercial importance petroleum Is called black gold.

Question 11.
What are alternatives to natural gas? Why do not we are using them?
Answer:
The alternatives for natural gas are coal bed methane and gas hydrates. These are not in commercial production phase due to lack in proper technology.

Question 12.
Can coal, petroleum and natural gas be prepared in the laboratory from dead organisms?
Answer:
No, their formation is very slow process and conditions for their formation cannot be created in the laboratory.

8th Class Physical Science 7th Lesson Coal and Petroleum 2 Marks Important Questions and Answers

Question 1.
How do you obtain various materials we are using in our daily life?
Answer:

Question 2.
What is biodiesel? How would you prepare biodiesel? What is its use?
Answer:
Biodiesel is one of the biofuel. Which is not toxic and renewable. It is made from the biological ingredients instead of petroleum or crude oil. Biodiesel usually made from the plant oils or animal fat through a series of chemical reactions.
It is used in diesel engines.

Question 3.
What is coal? Explain the process of formation of coal.
Answer:
Coal is hard and black coloured substance obtained from mines.

The plants in large and dense forests in low lying wet lands got buried under the soil due to natural processes like floods and earthquakes. As more soil deposited over them, the organic matter was compressed. The temperature also rose. As the organic matter sank deeper and deeper, under high temperature and high pressure, the dead plants slowly converted to coal.

Question 4.
What is coal tar and what are its uses?
Answer:
Coal tar: It is a black coloured thick liquid with an unpleasant smell. It is a mixture of about 200 substances.
Uses:
Products obtained from the coal tar are used as starting material for various substances like synthetic dyes, drugs, explosives, perfumes, plastics, paints and roofing material. Naphthaleine balls obtained from coal tar used to repel moths and other insects.

Question 5.
What is coal gas and what are its uses?
Answer:
Coal gas is a gas obtained during the processing of coal to get coke.
Uses:

1. It is used in lighting.
2. It is used as fuel in many industries.

Question 6.
What are petrochemicals? What are the uses of petrochemicals?
Answer: The useful substances which are obtained from petroleum and natural gas are called petrochemicals.
Uses:
They are used in the manufacture of detergents, synthetic fibres (polyester, nylon, acrylic) polythene, etc.

Question 7.
Draw a table showing uses of petrochemicals in various sectors.
Answer:

Question 8.
Why are coal and petroleum so versatile?
Answer:
Coal consists of mainly carbon while petroleum consists of mixture of compounds called hydrocarbons. These compounds make good starting materials for other compounds based on carbon. Carbon is very versatile and is basis for most of the materials.

Question 9.
Why does the price of petrol go up all the time?
Answer:
The price of anything depends on how much of it is available and how essential it is. Both coal and petroleum are exhaustible resources but we need them, both as fuel and as starting material for synthesising new compounds. Since supply is limited and becoming more expensive as the demand for petrol increase.

Question 10.
What is natural gas ? What are the advantages of CNG as fuel?
Answer: Natural gas is a very important fossil fuel.
CNG: Natural gas is stored under high pressure as compressed natural gas. Advantages of CNG as fuel:

1. CNG is less polluting and it is a cleaner fuel.
2. The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes because CNG travels large distances.

Question 11.
Ramu told Rahim that solar energy is inexhaustible resource then what are the questions raised in the mind of Rahim about solar energy?
Answer:

1. If it is inexhaustible resource of energy why don’t we are using it?
2. Whether utilization of solar energy is difficult?
3. Whether sophasticated techniques not available for proper use of solar energy at present?
4. It is costly to use solar energy for producing electric power?

Question 12.
Explain why petroleum is also called as liquid gold.
Answer:

1. They are many useful substances are obtained from petroleum which are called petrochemicals.
2. These are used in the manufacture of detergents, synthetic fibres such as polyester, nylon, acrylic, polythene, etc.
3. Due to great commercial importance petroleum is also called liquid gold.

Question 13.
What will happen if fossil fuels like coal and petroleum are completely exhausted?
Answer:

1. Coal and petroleum are the natural resources which are important resources of energy for us.
2. Coal is used as a fuel as such in homes and in industry, or it is used to generate electricity at thermal power plants.
3. Petroleum products such as petrol and diesel are used as fuels in transport to run scooters, motorcycles, cars, buses, trucks, trains and aeroplanes.
4. Kerosene and LPG obtained from petroleum are used as domestic fuels for cooking food.
5. Since the industrial revolution, we have been using increasing amount of energy. So we need more energy resource.
   So without coal and petroleum products life on the earth is impossible.

Question 14.
Suggest some alternative ways to save the fuel resources. (Or)
What actions are 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 are more utilized.

Question 15.
Burning fuels releases carbon dioxide , a green house gas, which causes climate changes and leads to global warming. Collect information about this through newspapers, magazines, etc. and prepare report.
Answer:
i) Drastic increase in the emission of CO₂ within last 30 years caused by burning of fossil fuels has been identified as the major reason for the change of temperature in atmosphere.
ii) Carbon dioxide in the atmosphere traps the reflect sunlight and re-emitt towards earth which is causing increase of earth temperature what we call as global warming.

Question 16.
Describe characteristics and uses of coke.
Answer:

1. It is tough, porous and black substance.
2. It is almost pure form of carbon.
3. Coke is obtained by heating soft coal in the absence or little supply of air.
4. It is used in the manufacture of steel and extraction of many metals.

8th Class Physical Science 7th Lesson Coal and Petroleum 4 Marks Important Questions and Answers

Question 1.
Is petroleum exhaustible? Explain.
Answer:

1. If we see the history of petroleum production, from 1859 to 1969, the total production of oil was 227 billion barrels.
2. 50% of this total was produced during the first 100 years, while the next 50% was extracted in just ten years.
3. Today our consumption rate of oil is far excess that of the rate of its formation.
4. Earth take more than one thousand years to form the oil that we consume in one day.
5. By about 2015, we would have consumed half of the total reserves of the oil.
6. It would become more and more difficult to extract oil in future.
   So petroleum is exhaustible.

Question 2.
Draw a diagram showing existence of various fuels like natural gas, petroleum in earth crust.
Answer:

Question 3.
Collect information about places where we get coal, petroleum and natural gas in India and mark the places on outline map of India.
Answer:
Coal: Jharia, Chandrapura, Bokaro, Giridih (Jarkhand), Ranigunj and Asansol (West Bengal), Singrauli (M.P.), Korba (Chhattisgarh), Singareni (A.P.) : Talcher and Rampur Himgir (Odisa) and Chand coal field (Maharashtra).
Petroleum : Digboi, Hugrijan, Moran, Naharkatiya, Sibsagar, Rudrasagar and Badarpur (Asom), Bombay High (Maharashtra), Ankleshwar, Kosamba, Kalol, Mehsana, Navagam and Dholka (Gujarat), Krishna and Godavari river basins (A.P.)
Natural gas: Cambay and Ankleshwar fields (Gujarat) and Bombay High (Maharashtra), Coastal Andhra Pradesh.

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

Question 1.
Write any two uses of petrochemicals in our daily life.
Answer:
Uses: They are used in the manufacture of detergents, synthetic fibres (polyester, nylon, acrylic) polythene, etc.

Question 2.
It is necessary to save the energy resources like petroleum and natural gas. Write a slogan about this to create awareness among people.
Answer:

1. ‘Save petrol and save future’.
2. ‘Save fuel and save earth’.

Question 3.
Petroleum is a complex mixture. Write the technique to separate its components.
Answer:
The technique to separate petroleum components is ‘fractional distillation’.

Question 4.
Write any two uses of Activated Carbon in our daily life.
Answer:
Uses of Activated Carbon:

1. Activated Carbon is used to purify liquids.
2. It is used to treat many types of oral poisonings.

Question 5.
Assume that you are a driver, what measures do you take to save petrol?
Answer:
Engine must be stopped in the traffic signals or in heavy traffic.

Question 6.
The following table shows the total power shortage percentage in India from 1994-1997. Observe the data and give the answers to the following questions.
i. In which year the shortage percentage of power is least?
ii. Between which two years the shortage percentage difference is more?
iii. In which year the shortage percentage of power is maximum?
iv. Make a comment on shortage percentage of power between 1994-95.
Answer:
i. 1995
ii. Between 1996 and 1997
iii. 1997
iv. Shortage percentage is decreased by 0.3 in between 1994 – 95.

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 5 Metals and Non-Metals Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 5th Lesson Metals and Non-Metals

8th Class Physical Science 5th Lesson Metals and Non-Metals Textbook Questions and Answers

Improve Your Learning

Question 1.
Explain the physical properties of metals with suitable examples.
(OR)
Explain briefly the physical properties of metals.
Answer:
Physical properties of metals:

1. Lustrous:
   When we rub the surface of metals with sand paper they will shine. This property is called lustrous, e.g.: Iron, zinc etc.
2. Sonority:
   When we hit the metal surface they give a ringing sound is called sonority, e.g.: Iron, copper etc.
3. Malleability:
   Metals can be flattened into thin sheets. The property of flattening metals into thin sheets is called malleability, e.g.: Silver, Iron, copper.
4. Ductility:
   Metals can be drawn into wires.
   The property of drawing a metal to make fine wire is called ductility, e.g.: Silver, gold.
5. Electric conductivity:
   Electricity can be easily pass through metals. So they are called good conductors of electricity.
   e.g.: Silver, copper, iron.
6. Conductivity of heat:
   Metal absorbs heat quite easily. They are good conductors of heat, e.g.: Copper, iron.

Question 2.
You are given two samples. How do you distinguish which is metal and which is non-metal?
Answer:

1. By physical properties, generally we can judge whether the given sample is metal or non-metal that is metals are hard. They are lustrous, sonorous, malleable, ductile and good conductors of heat and electricity.
2. Generally metal sample react with water and non-metal sample does not react with water.
3. Generally metal sample react with acid and produce hydrogen gas whereas non-metal samples does not react with acid.

Question 3.
Which metals are used in making jewellery? Why?
Answer:
Generally we use metals like gold, silver and copper for making jewellery due to their high ductility and lustrous surface.

Question 4.
Which substance liberate hydrogen when react with metals?
Answer:
Generally acids react with metals and liberate hydrogen gas. Water also react with some metals and liberate hydrogen gas.

Question 5.
In a chemical reaction iron is unable to displace zinc from zinc sulphate. Why?
Answer:
Zinc is more reactive than iron. A less reactive metal cannot displace a more reactive metal from its salt solution. So iron unable to displace zinc from zinc sulphate.

Question 6.
Why cooking pans do not have metal handles?
Answer:
Metals are good conductors of heat. So they gain heat easily. So in order to avoid the burning of our palms, the handles of cooking pans made of heat resist material such as plastic.

Question 7.
Sulphur dioxide is
A) basic oxide
B) acidic oxide
C) neutral oxide
D) amphoteric oxide
Answer:
B) acidic oxide

Question 8.
Match the following.
Group – A                                             Group – B
1. Making into thin sheets        ( )        A) Ductility
2. Shining materials                  ( )        B) Conductivity
3. Making into wires                 ( )        C) Sonority
4. Transmission of heat            ( )        D) Lustrous
5. Making ringing sound          ( )         E) Malleability
Answer:
1. E
2. D
3. A
4. B
5. C

Question 9.
Which gas makes a ‘pop’ sound if exposed to lighted matchstick?
Answer:
Hydrogen gas makes a pop sound when it is exposed to a lighted matchstick.

Question 10.
Why are bells made up of metals instead of wood
Answer:
Metals have sonority property that means they make ringing sound when we hit them with a hammer. Where wood does not give ringing sound when it is hit with a hammer. So bells are made up of metals instead of wood.

Question 11.
Imagine the human life without metals, write briefly about the consequences.
Answer:

1. There would not be any utensil for cooking.
2. There would not be trains, buses, aeroplanes for travelling.
3. There would be no almirahs, no school bells, no agricultural material, no electrical appliances, no automobiles, no satellites, no machinery and no decorative material. So everything in life directly or indirectly depends upon metals. So we cannot imagine a life without metals.

Question 12.
After completion of metals and non-metals chapter, Raheem understood that metals are hard and non-metals are soft. During the discussion with his brother he came to know that diamond is a hardest material and it is a non-metal. Similarly mercury is a soft material and it is a metal. These findings from the discussion raised some questions in Raheem’s mind. Can you guess those questions? Write them.
Answer:
The doubts arised in Raheem’s mind are

1. If diamond is hard how it behaves like a non-metal?
2. If mercury is soft material how it acts as metal?
3. What are the properties which actually decide whether the given material is either metal or non-metal?

Question 13.
Discuss the acidic and basic nature of the metals and non-metals with suitable experiments.
Answer:
Take a small strip of magnesium and burn it. It forms white ashes of magnesium oxide collect the ashes of magnesium and add some distilled water to it. Test the solution with red and blue litmus papers. Note the colour changes. The solution turns red litmus into blue. It indicates given solution is basic. So metallic oxides are basic in nature.
Take a small amount of powdered sulphur in a deflagrating spoon and heat it. As soon as sulphur starts burning, introduce the spoon into a gas jar or tumbler. Cover the tumbler with lid to ensure that the gas produced does not escape. The gas formed is sulphur dioxide. Remove the spoon after some time but try to keep the jar covered. Add a small quantity of water into the tumbler and quickly replace the lid. Shake the tumbler well. Check the solution with red and blue litmus paper. The solution turns blue litmus into red. It indicates the solution is acidic. So non-metallic oxides are acidic in nature.

Question 14.
How do you appreciate wide range utility of aluminium right from utensils to space craft?
Answer:
Aluminium is essential part of our life. Aluminium foil is used on inner packing of food materials and toffees. Aluminium and copper mixture is used in currency coins, medals and statues. Aluminium is used in electrical appliances, automobiles, satellites, space crafts, aeroplanes, cooking utensils, machinery, decorative materials. This indicates wherever we go we observe articles made up of aluminium. So we require aluminium for better living.

Question 15.
How is malleability of metals used in our daily life
Answer:
Metals can be flattened into sheets is called malleability. Due to this metals can be made into different shapes like railway coaches, railway tracks, cooking utensils, etc. So malleability of metals is extremely useful in daily life.

Question 16.
Dumping of waste material made up of metals and non-metals leads to environment pollution. Do you support the statement? Give your justification with suitable examples.
Answer:
Soil samples analyzed from location adjacent and with in deposite show high level of heavy metals in particular lead, mercury, cadmium, copper and chromium. In which lead and mercury are extremely harmful to environment as well as mankind. After medical evaluation the adolescents living and children living near dump site had high incidence of diseases that are associated with high exposure levels to these metal pollutants. So waste material made of metals and non-metals leads to environmental pollution. Some more examples are burning of sulphur forms sulphur dioxide and sulphur trioxide, which is a cause for acid rain and soil corrosion. In complete burning of carbon leads to release of poisonous carbon monoxide.

8th Class Physical Science 5th Lesson Metals and Non-Metals InText Questions and Answers

Think and Discuss

8th Class Physical Science Textbook Page No. 68

Question 1.
How will you close the circuit using sulphur, carbon or iodine? They may be in powder form. Try to tightly pack the powder in a straw and use it. Think of other ways!
Answer:
Circuit will not be completed by using non-metals like sulphur, carbon or iodine because they are bad conductors of electricity. So by packing the powder will not complete the circuit. There is no other by using which we can complete the circuit by using a non-metal.

Try This

8th Class Physical Science Textbook Page No. 74

Question 1.
Recall the names of the some of the laboratory acids and bases that you know. Write down their names in table and identify metal/non-metal present in them, which form oxides when react with oxygen. Take the help of your teacher.
Answer:

Question 2.
Have you seen a periodic table?
Answer:
Yes.

Question 3.
Try to find the metals and non-metals that you come across in the chapter on the periodic table.
Answer:
Metals               Non-metals
1) Zinc               1) Sulphur
2) Copper          2) Chlorine
3) Iron               3) Nitrogen
4) Potassium     4) Carbon
5) Sodium         5) Phosphorus
6) Gold
7) Silver
8) Magnesium
9) Calcium
10) Aluminium

8th Class Physical Science 5th Lesson Metals and Non-Metals Activities

Activity – 1

Question 1.
Observing appearance and colour of some materials:
Observe the appearance of your samples. Look at their colour. Decide whether they appear shining or dull and record your observations in table. If the surface seems dirty, clean it with sand paper.

a) Which of the samples did not shine even after you cleaned them with sand paper?
Answer:
Sulphur, carbon.

b) Generally metals are lustrous. Do all lustrous materials are metals?
Answer:
No. Some may be non-metals, e.g.: Iodine

c) We all know that mirror is lustrous. Can a mirror be called metal?
Answer:
No. Several properties required to decide if a given material is metal or not.

Activity – 2

Question 2.
Listening the sound produced by some material:

a) Drop a piece of coal on the floor and listen the sound.
Do you think coal is sonorous?
Answer:
No.

b) Take the pieces of zinc, copper, aluminium, magnesium and tightly packed packets of sulphur, carbon and iodine. Drop them one by one, on a hard surface. Listen carefully to the sound produced and record your observation in table.
Answer:

c) What similarity do you notice among materials which produce sound?
Answer:
All of them are metals.

d) Which property of metals first attracted the attention of human beings?
Answer:
Metals had the advantage of not just being harder but they could be heated in a fire and moulded or cast into different shapes. This property of metals first attracted the attention of human beings.

e) Do you bring a similar change in the shape of a clay material by beating it?
Answer: Yes, we bring similar change in the shape of a clay material by beating it.

Activity – 3

Question 3.
Identifying malleability of material:
Take a hammer and beat the material samples which are used in Activity-2 and observe the changes in material samples. Record your observations in the table.
Answer:

Some of the samples like zinc, copper are flattened whereas some materials such as carbon, iodine broken into pieces.
The materials which can be flattened into thin sheets are called malleable materials.
Ductility:
We use wires in different situations in our daily life. Look at the samples given in the table.

a) Have you ever seen the wires made up of materials mentioned in the above table?
Answer:
Yes. I have seen the wires made of iron, copper, aluminium.

b) What is the property of drawing material to make wire is called?
Answer:
Ductility.

Activity – 4

Question 4.
Identifying electric conductivity of a material:
Arrange an electric circuit with a battery and bulb. Close the circuit using an iron nail, as shown in figure. Observe whether the bulb glows or not. Record your observations in table. Repeat the same experiment using the other samples and record your observations in the same table.

a) Do all the samples allow the bulb to glow?
Answer:
No. Materials like iron, zinc, copper allows bulb to glow.

b) What is name given to these material which allows electricity to pass them and make to bulb to glow are called?
Answer:
They are called conductors.

c) Give examples for good conductors of electricity?
Answer:
Copper, iron, aluminium

d) Talk to an electrician. Look at the handles of his tools. Are the handles made of the same materials? If not why?
Answer:
No. The handles of his tools are made of electrical insulating material in order to avoid electrical shock.

Activity – 5

Question 5.
Observing heat conduction by metals:

Take an iron rod. Stick pins on it with the help of wax. Now fix the rod to a stand as shown in figure. Heat one end of the rod with a spirit lamp and see how the pins fall off?

a) Why did the pins fall off from iron rod?
Answer:
Iron rod gains heat from spirit lamp.

b) Pin of which end fell off first?
Answer:
The pin which is near to spirit lamp falls first.

c) What could be the reason for this?
Answer:
The pin falls off because of heat supplied to the iron rod and makes the wax to melt at one end. The wax closer to the flame melted first and the pin falls off. Then the other pins falls. This activity shows that heat moves from one end of the rod to the other. This property of a material is known as conductivity of heat.

d) Go back to the list of samples. On the basis of all the activities carried out, fill the following table.
Answer:

Lab Activity

Conduct an experiment to know the reaction of oxygen with metals and non-metals.
Answer:
Aim: To know reaction of oxygen with metals and non-metals.
Materials required: One metal sample (Magnesium) and one non-metal sample (Sulphur), spirit lamp or Bunsen burner and litmus paper, etc.
Procedure:
Take a small strip of magnesium and burn it. It burns brilliantly and produce white ashes of magnesium oxide due to reaction between magnesium and oxygen. Collect the ashes of magnesium and add some distilled water to it. Test the solution with red and blue litmus papers. Note the changes in table.

Take a small amount of powdered sulphur in a deflagrating spoon and heat it. Sulphur starts burning and forms sulphur dioxide. Introduce the spoon into a jar and cover the jar with a lid to ensure that the gas produced does not escape. Add small quantity of water into the jar quickly replace the lid. Shake the jar well. Check the solution with blue and red litmus papers. Record the changes in table.

From the table we can observe metallic oxide solutions are basic in nature whereas non metallic oxide solutions are acidic in nature.

Activity – 6

Question 6.
Experiment about reaction of metals with water.
Answer:
Take a 500 ml beaker or a big trough and fill half of it with water. Cut a small piece of sodium (which is kept in kerosene) and put the sodium piece in water using forceps. This piece of sodium floats on the surface of water with a hissing sound.

This shows that sodium is reacting extremely fast with water.
Repeat the same experiment using aluminium, and iron. We will not see any change even after five minutes. This is because these metals react extremely slow with water. This shows metals react with water at different rates.

Activity – 7

Question 7.
Reaction with Acids.
Fill the reactions of the following metals and non-metals with dilute hydrochloric acid and dilute sulphuric acid.
Iron, Zinc, Copper, Sulphur, Aluminium, Graphite, Magnesium and Iodine.

Observation:
We find that some metals react with dilute HCl or H₂SO₄ liberating hydrogen but non-metals usually do not react with acids.

Activity – 8

Question 8.
Reactivity of metals:
Take six beakers and label them a, b, c, d, e and f. Take 50 ml of water in each beaker and dissolve a spatulaful of copper sulphate in beakers ‘a’ and ‘b’. Dissolve a spatulaful of zinc sulphate, in beakers ‘c’ and ‘d’. Iron sulphate in beakers ‘e’ and ‘f’.

• Zinc granules in beaker ‘a and e’
• Iron nail in beaker ‘b and d’
• Copper turnings in beaker ‘c and f’

Leave the beakers undisturbed. Record the changes in the colour of the solution in the table.

a) What could be the reasons behind these changes?
Answer:
In beaker ‘a’, zinc displaces copper from copper sulphate giving rise to colourless zinc sulphate. Iron displaces copper from copper sulphate in beaker ’b’ leaving light green colour of iron sulphate and zinc displaces iron from Iron sulphate by change the colour from light green to colour less:
Copper sulphate + Zinc → Zinc sulphate + Copper
Copper sulphate + Iron → Iron sulphate + Copper
Iron sulphate + Zinc → Zinc sulphate + Iron

b) Do you find any changes in beakers c, d and f?
Answer:
There is no change in beakers c, d and f. The reason is

1. Copper is unable to displace zinc from zinc sulphate in beaker ‘c’.
2. Copper is unable to displace iron from iron sulphate in beaker ‘f’.
3. Iron is unable to displace zinc from zinc sulphate in beaker ‘d’.

c) Why does iron is unable to displace zinc from zinc sulphate?
Answer:
Iron is less reactive than zinc. A more reactive metal can replace a less reactive metal from its salt solution. But a less reactive metal unable to displace a more reactive metal from its salt solution.
The order of reactivity of given metals are Zinc > Iron > Copper

AP State Syllabus AP Board 8th Class Physical Science Solutions Chapter 3 Matter Around Us Textbook Questions and Answers.

AP State Syllabus 8th Class Physical Science Solutions 3rd Lesson Matter Around Us

8th Class Physical Science 3rd Lesson Matter Around Us Textbook Questions and Answers

Improve Your Learning

Question 1.
Describe an activity which provides the evidence for
a) the motion of particles
b) attraction between particles
c) inter-particle space
Answer:
a) An activity which provides the evidence for the motion of particles:
Materials required: Two 250 ml round bottom flasks, red or blue ink, dropper, Potassium permanganate (KMnO₄) solution.
Procedure:

1. Take two 250 ml round bottomed flasks and fill them with water.
2. Use a dropper and put a few drops of blue or red ink slowly along the sides of first flask.
   
3. Use a dropper and put one or two drops of KMnO₄ solution along the sides of second flask.
4. We observe that in the first flask the ink drops slowly diffusing and mix with water, so as to change the colour of water to red/blue.
5. In the second flask we observe that the KMnO₄ solution diffuses fast in the water and the colour of water changes.
6. This activity provides an evidence for the motion of particles.

b) An activity which provides the evidence for the attraction between particles:

1. Open a water tap and allow the water to reach the ground.
2. Now try to break the stream of water with your finger.
3. We can break the stream momentarily, but not permanently.
4. The reason behind the stream of water remaining together is the force of attraction between the water particles.
5. Now try to break a piece of iron nail with your hands.
6. We cannot break it, because the force of attraction between the particles of nail is very high.
7. Do the same with a piece of chalk. We can break it easily, due to the weak attraction forces among the particles of piece of chalk.
8. From the above, we can say that the particles of matter have attractive forces among them to keep the particles together.
9. These forces of attraction are not equally strong in all the forms of matter.

c) An activity which provides the evidence for the inter-particle space:
Materials required: Beaker, water, salt, spoon and a glass rod.
Procedure:

1. Take a graduated beaker and fill it with some water and mark the level of water.
2. Add some salt and stir it thoroughly with a glass rod.
3. Observe the change in water level. There will be no change in it.
   
4. Add some more salt and stir it again.
5. Observe the change in water level. There will be no change.
6. Continue this process till you see some salt remains undissolved in water.
7. From this activity, we can say that solid and liquid particles have some space between them.
8. The solid particles enter into the space between the liquid particles on dissolving solid in liquid.
9. This process continues till all the space in liquid particles is occupied by solid particles.
10. After completion of this occupation, the solid particles, as there is no space to occupy remain undissolved.

Question 2.
Name the characteristics of matter that are demonstrated by diffusion.
Answer:
The characteristics of matter that are demonstrated by diffusion:

1. Matter is made up of tiny particles.
2. Particles of matter have space between them.
3. Particles of solids and liquids diffuse into liquids.
4. Particles of gases diffuse into gases.
5. Rate of diffusion of gases is higher than that of liquids or solids.
6. Particles of solids occupy the space between the particles of liquids on addition of a solid to a liquid.
7. Particles of matter move continuously in liquids and gases.

Question 3.
“When sugar is dissolved in water, there is no increase in volume.” Is it true or false? Comment on the statement keeping in mind the amount of sugar, amount of water, etc.
Answer:
This statement is true.
Reason: When sugar is dissolved in water, the particles of sugar occupy the space between the particles of water. Hence there is no change in the volume of water.
Conditions for observing the change in volume of water:
If we go on adding sugar without increasing the quantity of water, there will be no space between water particles, to be occupied by sugar particles. Hence the sugar remains undissolved.

Question 4.
Is there any change in mass when a substance changes its state? Explain with example.
Answer:

1. Take a beaker and fill it with ice cubes.
2. Find the mass (m₁) of the beaker along with ice cubes using a spring balance.
3. Keep the beaker at rest for some time, till the ice changes into water.
4. Then find the mass (m₂) of the beaker along with water.
5. We observe that m₁ = m₂.
6. We conclude that the mass never changes when a substance changes its state.

Question 5.
Do all substances change from solid to liquid and liquid to gas on heating ? Explain. Ans. All substances cannot change from solid to liquid and liquid to gas on heating.
e.g.:

1. When wood is heated, it cannot change its state from solid to liquid, but the form of substance changes.
2. Mercury/blood.

Question 6.
Define the following terms:
a) Melting point
b) Boiling point
c) Evaporation
Answer:
a) Melting point: The temperature at which a solid melts to become a liquid is called “melting point”.
b) Boiling point: The temperature at which a liquid starts boiling at the atmospheric pressure is known as its “boiling point”.
c) Evaporation : The phenomena of change of a liquid into vapours at any temperature below its boiling point is called “evaporation”.

Question 7.
Correct the following statements.
a) Water boils at 100°C under atmospheric pressure.
Answer:
This is a correct statement.

b) A liquid evaporates above its boiling point.
Answer:
This statement is incorrect.
Reason: Evaporation takes place at any temperature below its boiling point.

c) Solids have the largest inter-particle space.
Answer:
This statement is incorrect.
Correct Statement: The inter-particle space of solids is minimum.
Explanation: The force of attraction between the particles is also very high due to less inter-particle space. Hence solids have definite shape and a fixed volume.

d) Gases have the strongest inter-particle forces.
Answer:
This statement is incorrect.
Correct Statement: Gases have weakest inter-particle forces.
Explanation: The inter-particle space for a gas is maximum. Hence the inter-particle forces are also weak. Due to this gases have no definite shape or fixed volume. They have to be stored in a closed container always.

Question 8.
Why do we prefer to sip hot tea with a saucer rather than a cup ?
Answer:

1. The surface area of saucer is more than the surface area of a cup.
2. We know that the rate of evaporation increases with an increase of surface area.
3. The hot tea particles can easily escape from the saucer than a cup.
4. Hence hot tea becomes cold easily in a saucer than a cup.
5. So we prefer to sip hot tea with a saucer rather than a cup.

Question 9.
When water solidifies to ice then heat is
a) Liberated
b) Absorbed
c) No change
d) Depending upon the condition heat may absorbed or liberated.
Answer:
a) Liberated

Question 10.
Convert the following temperatures to the Celsius scale.
a) 283 K   b) 570 K
Answer:
a) We know that 273 K = 0°C
283 K = 283 – 273 = 10°C
∴ 283 K = 10°C

b) We know that 273 K = 0°C
570 K = 570 – 273 = 297
∴ 570 K = 297°C

Question 11.
Convert the following temperatures to the Kelvin scale,
a) 27°C   b) 367°C
Answer:
a) 27°C = 27 + 273 = 300 K
b) 367°C = 367 + 273 = 640 K

Question 12.
Fill in the blanks.
a) Matter changes from one state to another either raising the …………… or lowering the ……………..
b) A change in which a solid on heating directly changes into vapour state is called …………….
Answer:
a) temperature, temperature
b) sublimation

Question 13.
Match the following.
a) Conversion of liquid into gas      ( )        (i) gas
b) Non – compressible                    ( )        (ii) solid
c) Maximum expansion                   ( )        (iii) particle
d) Constituents of matter                ( )        (iv) evaporation
Answer:
a) iv
b) ii
c) i
d) iii

Question 14.
How can we smell perfume sitting several meters away from the source?
Answer:

1. We know that the particles of gas are highly mobile in the air.
2. The particles of perfume vapours also move in air for several meters.
3. Hence we can smell perfume, sitting several meters away from the source.

Question 15.
Steam produces more severe burns than boiling water. Think why?
Answer:

1. Steam particles have more energy than the particles of boiling water.
2. This is because particles in water vapour have absorbed additional energy in the form of latent heat of vaporization.
3. So, steam produces more severe burns than boiling water.

Question 16.
Make a model to explain the structure of particles in solids, liquids and gases.
Answer:
Students have to prepare their own models.

Question 17.
How do you appreciate sweating mechanism of human body to control the temperature of the body?
Answer:

1. When we do some physical exercise or hard work, sweating is observed on the body.
2. The sweat evaporates from the surface of our body by absorbing the heat from your body.
3. Thus the particles of liquid absorb energy from our body and escapes to the surroundings.
4. Due to this we feel cool.

Different shaped containers, Beaker, Measuring jar, Conical flask, Round bottomed flask, Test tubes, CNG related Pictures, 50 ml syringe, Incense stick, Scent bottle, Potassium permanganate, Copper sulphate, Long glass tube with scale, Liquid Ammonia, Hydrochloric acid, Cotton, Two rubber corks, Two tongs, Dropper, Water, Salt, Thermometer, Spirit lamp, China dish.

8th Class Physical Science 3rd Lesson Matter Around Us InText Questions and Answers

8th Class Physical Science Textbook Page No. 31

Question 1.
Is there any substance which can be found in three states like water?
Answer:
Yes. The substance which can be found in three states like water is wax.

Question 2.
What are the properties that lead us to consider petrol or milk as liquids?
Answer:
Petrol and milk are considered as liquids because they have no fixed shape. But they get the shape of the container in which they have been poured.

Question 3.
Do solids have definite shape and fixed volume?
Answer:
Yes, solids have definite shape and fixed volume.

8th Class Physical Science Textbook Page No. 32

Question 4.
What is the shape of the water in different containers?
Answer:
Water gets the shape of containers in which it has been poured.

Question 5.
Is it same in all cases or different?
Answer:
Yes, it is same in all cases.

Question 6.
What shape does water take if it spills on the floor?
Answer:
Water spreads on floor if it spills on the floor.

Question 7.
Are the levels of water and milk same?
Answer:
Yes, the levels of water and milk are same.

Question 8.
Can you guess the volume of oil?
Answer:
Volume of the oil is equal to 50 ml.

Question 9.
What does a fluid mean?
Answer:
Fluid is a substance which can flow easily.

8th Class Physical Science Textbook Page No. 33

Question 10.
Does CNG have a fixed volume?
Answer:
No, CNG does not have a fixed volume.

Question 11.
Does CNG have a definite shape?
Answer:
No, CNG doesn’t have a fixed shape. Its shape is depending on the containers.

8th Class Physical Science Textbook Page No. 34

Question 12.
Does the smell from burning incense stick and deodorant spray reach someone on the other end at the same time?
Answer:
The smell from deodorant spray reaches someone on the other end faster than the smell from incense stick.

8th Class Physical Science Textbook Page No. 36

Question 13.
Why do gases diffuse faster than solids and liquids?
Answer:
The molecules in the gas are far from each other i.e., the inter molecular space is very high than in solids and liquids. Hence they have less attractive power. So, gases diffuse faster than solids and liquids.

Question 14.
When does water change into ice and then into vapour?
Answer:
Water when cooled in a refrigerator, it becomes ice. (Decreasing the temperature).

8th Class Physical Science Textbook Page No. 39

Question 15.
What type of changes occur inside the matter during a change of state?
Answer:
Inside the matter, we observe the increase/decrease in volume during the change of state.

Question 16.
How does this change of state take place?
Answer:
Change of state takes place by change in temperature.

Question 17.
What does happen to the particles of matter during a change of state?
Answer:
During a change of state, the kinetic energy of particles may increase/decrease, resulting in the increase/decrease of inter molecular attraction.

8th Class Physical Science Textbook Page No. 41

Question 18.
What will does happe when we apply pressure and compress a gas enclosed in a cylinder?
Answer:
When pressure is applied and compressed the volume of a gas in a cylinder decreases. (According to Boyle’s law).

Question 19.
Will the particles come closer?
Answer:
Yes, the inter molecular space between the particles decreases and they come close.

Question 20.
Do you think that increasing or decreasing the pressure can change the state of matter?
Answer:
Change in pressure can change the state of matter.

Question 21.
Can we liquify gases by applying pressure or reducing temperature?
Answer:
Gases can be liquefied by cooling below its critical temperature. Hence, change in temperature and pressure causes the gases to liquefy.

Question 22.
Do we always need to supply heat or change the pressure for changing the state of matter?
Answer:
It is required. But in some cases like natural evaporation of water, it is not necessary.

Question 23.
Can the change of state from liquid to vapour take place without the liquid reaching its boiling point?
Answer:
Yes, it is possible in case of drying the wet clothes. In the process, water direly changes into vapour form without reaching its boiling point.

Question 24.
Can you give few more examples for evaporation?
Answer:
Evaporation of iodine, drying up of wet body, etc.

Question 25.
What could be the reasons for this type of changes in states?
Answer:
In liquid s, the particles at the surface possess higher energy than particles in the bulk of watt.. The particles on the surface are able to break away from the force of attraction of other particles and change into vapour state.

Think & Discuss

8th Class Physical Science Textbook Page No. 34

Question 1.
Rubber band Activity:
a) Let us stretch a rubber band. Is there a change in its shape?
b) Is rubber band solid or liquid? Why?
Answer:
a) When rubber band is stretched it changes its shape.
b) It is a solid. If stretching is stopped, the rubber band regains its shape. If the stretching is too much, the rubber band permanently loses its shape.
Reason : Rubber band is a solid, but the nature of particles by which the rubber band is made is responsible for the above phenomena.

Question 2.
Powdered salt Activity:
a) Which shape does the powdered salt take?
b) Can you say that salt is a liquid on the basis of change in its shape? Justify your answer. Take a sponge. Observe its shape.
Answer:
a) Powdered salt takes the shape of the container, b) It is a solid.
Justification:

1. Change in shape or state means a complete change in the arrangement of particles.
2. Powdered salt is a composition of tiny particles, which do not change their shape.

Question 3.
Sponge Activity:
Can you compress it? Is it a soild? Why? Think. Is anything coming out from the sponge when it is compressed.
Answer:

1. Sponge can be compressed.
2. It is a solid.

Justification :

1. The inter-particle space is slightly more than a rigid body.
2. So that it can be compressed.

Question 4.
Why can’t you able compress a wooden block ? (or) Why aren’t you able to compress a wooden block ?
Answer:

1. The inter-particle space is very less in a wooden block.
2. So we cannot compress it at ordinary conditions.

8th Class Physical Science Textbook Page No. 42

Question 5.
Why do we wear cotton clothes in summer?
Answer:

1. More sweat is produced from our body during summer due to excess of external temperature.
2. We feel cool when the sweat is evaporated.
3. On wearing cotton clothes, the clothes absorb sweat from our body. So, we feel cool.
4. Other clothes like silk, polyester, etc. cannot absorb sweat.
5. Hence we wear cotton clothes in summer.

Question 6.
Why do we see water droplets on outer surface of a glass containing ice-cold water?
Answer:

1. Ice-cold water in the glass cools its surface.
2. Air around the glass contains water vapour which is warmer than the surface of the glass.
3. Due to the cold glass, air close to its surface will also become cooler.
4. This changes the water vapour in the air around the surface of the glass into water.
5. This water forms small drops on the outer surface of the glass.

Question 7.
Why do pigs toil in the mud during hot summer?
Answer:

1. Generally, the temperature of body is controlled through the sweating evaporation.
2. In the case of pigs, these have less sweat pores on their skin surfaces. So sweating evaporation process does not take place.
3. Because of this type of arrangement in pigs, they toil in the mud ponds more time during hot summer.

8th Class Physical Science 3rd Lesson Matter Around Us Activities

Activity – 1

Identifying the shape and volume of liquids
Question 1.
(a) Prove that the liquids have no fixed shape.
Answer:

1. Collect transparent containers of different shapes.
2. Take some water using the measuring jar.
3. Pour the water in one of the containers.
4. Observe the shape of water.
5. Pour the same water in different containers and observe the shape of water.
6. We observe that the water (liquid) takes the shape of container.
7. We can say that liquids have no fixed shape.
   

(b) Prove that the liquids have fixed volume.
Answer:

1. Take 50 ml of water with a measuring jar.
2. Pour this water in a transparent beaker.
3. Mark the level of water on the beaker and throw the water out.
4. Now measure 50 ml of milk, and pour it in the same beaker.
5. Mark the level of milk on it, and remove milk from the beaker.
6. Now take 50 ml of oil and pour it in the same beaker.
7. Mark the level of oil on it, and remove the oil from the beaker.
8. We observe that the mark on the beaker is same for water, milk and oil.
9. This proves that the liquids have a fixed volume.

Activity – 2

Question 2.
Do the gases have a definite shape and a fixed volume?
Answer:
CNG (Compressed Natural Gas) is stored in a tank. In vehicles CNG is stored in cylinders. We observe that CNG and all other gases neither have a fixed shape nor fixed volume.

Activity – 3

Observing the compressibility of different materials
Question 3.
Prove that the gases are highly compressible than liquids and solids.
Answer:

1. Take a 50 ml syringe.
2. Draw the piston to suck in air.
   
3. Place your finger on the nozzle and press.
4. Observe depth of piston moved into syringe and note the height of air column.
5. We feel hard to press the piston after certain height.
6. Here the air in the syringe is compressed.
7. Now fill water in the syringe and do the same experiment.
8. Note the height of water column when you feel hard to press the piston.
9. Here the height of water column is more than the height of air column.
10. Now take a piece of wood or iron and press it with your thumb.
11. We cannot find any observable change in its volume.
12. From the above observations, we can say that gases are highly compressible than liquids and solids.

Activity – 4

Observing the diffusion of gases
Question 4.
Describe an activity to observe the diffusion of gases.
Answer:

1. Ask your friend to hold an unlit incense stick and stand in one corner of the room.
2. Then you go and stand in the other corner.
3. We cannot observe any smell (This depends on the type of incense stick).
4. Now ask your friend to light the incense stick.
5. After a few seconds, we can observe the smell of incense stick.
6. The scent in the vapour form and smoke mixes with air and moves across the room and reaches our nose.
7. This activity proves that the gases can diffuse.

Activity – 5

Observing the diffusion of liquids
Question 5.
Write an activity which shows the diffusion of liquids.
Answer:
Take 250 ml round bottomed flask with 2/3rd water in it. Use a dropper and put a few drops of blue or red ink or Potassium permanganate (KMnO₄) solution slowly along the sides of the flask.

We can observe that liquids also diffuse into each other like gases.

Activity – 6

Observing the diffusion of particles of solids into liquids
Question 6.
Prove that the particles of solids diffuse into liquids.
Answer:

1. Take a beaker full of water.
2. Add a few crystals of potassium permanganate to it.
3. We observe that the diffusion of potassium permanganate crystal into water and the colour of water changes.
4. Repeat the experiment with crystals of copper sulphate.
5. Here also we observe the diffusion of CuSO₄ crystals into water and the colour of water changes.
6. From the above observations, we found that the particles of solids diffuse into liquids.

Lab Activity Diffusion of two gases
Question 7.
Describe an experiment to measure the speed of diffusion of two gases.
Answer:
Aim: To observe the speed of diffusion of two gases.
Materials required : Long glass tube with scale, liquid ammonia, Hydrochloric acid (HC/), pieces of cotton, two rubber corks and two tongs.

Procedure:

1. Take a one meter long narrow glass tube.
2. Take two pieces of cotton wool.
3. Soak one piece of cotton wool in HCl solution.
4. Soak another piece of cotton wool in NH₃ solution.
5. Insert them separately at the two ends of the tube with the help of tongs.
6. Close the ends of the glass tube with rubber cork and observe.
7. The HCl gives off hydrogen chloride gas and ammonia solution gives off ammonia gas.

Observation:

1. Both gases react together to form a white ring in the tube due to formation of ammonium chloride.
2. Measure the distance of white ring from two ends of the glass tube.

Explanation:
We can observe that the ammonia gas travelled faster. So that the distance of white ring is more from ammonia end than hydrochloric acid end.

Activity – 7

Question 8.
How small are the particles of matter?
Answer:

1. Take a beaker with water. Mark the level of water.
2. Add 1 or 2 crystals of potassium permanganate and dissolve in water.
3. Colour of water changes to light violet.
4. Now take out approximately 10 ml of this solution and add it to 90 ml of clear water in another beaker.
5. Now the colour of water will be lighter than in the previous one.
6. Again take out 10 ml of this solution and add it to another 90 ml of clear water.
7. Carry out this process 4, 5 times and observe the changes in colour of the solution.
8. We observe the water in last beaker also changed to light violet.
9. From this activity we conclude that both solids and liquids are made up of tiny particles.

Activity – 8

There exists space between particles
Question 9.
Write an activity which shows the space between particles.
Answer:

Procedure: Take a graduated beaker and fill it with some water and mark the water level. Add some salt and stir it thoroughly with a glass rod. Observe if there is any change in water level. Add some more salt and stir it again.
Observations: From the activity we can conclude that both solid and liquid particles have some space between them. Hence the solid particles enter into the space between the liquid particles on dissolving solid in liquid. So there is no change in the water level.

Activity – 9

Observing the force of attraction between the particles of matter
Question 10.
Write an activity which provides an evidence for the force of attraction between the particles of the matter.
Answer:
Procedure:
Open a water tap and allow the water to reach the ground. Now try to break the stream of water with our finger. But we cannot break the stream permanently.
We cannot also break a piece of iron nail with our hands. But we can break a piece of chalk with our hands.
Observations: From the above observations we can say that particles of the matter have forces acting between them that keeps the particles together.
It is also clear that this force is not equally strong and different in different forms of matter.

Activity – 10

Effect of temperature on change of state
Question 11.
Write an activity to know the effect of temperature on change of state of matter.
Answer:

1. Take about 100 g of ice in a beaker.
2. Suspend a laboratory thermometer so that its bulb is in contact with the ice.
3. Set up the beaker as shown in the figure.
4. Note the temperature.
5. Now heat the beaker slowly.
   
6. Record the change in temperature after every 30 seconds.
7. Let the ice melt completely.
8. Now place a glass rod in the beaker and continue heating till water starts boiling.
9. After some time all the water will get vapourised.
10. From this we understand that substances around us change state from solid to liquid and from liquid v to gas on application of heat.
11. There are some substances which can change directly from solid state to gaseous state and vice versa without changing into the liquid state.

Activity – 11

Effect of surface area, humidity and wind speed on evaporation
Question 12.
(a) Explain the effect of surface area on the rate of evaporation.
Answer:
Rate of evaporation increases with an increase of surface area.
Explanation:

1. During evaporation process, the particles escape from the surface of liquid.
2. The increase in the surface area provides more scope for particles to escape from the surface.
3. Hence it leads to increase the rate of evaporation.

Ex: Water in a China dish evaporates faster than the water in test tube.

(b) Explain the effect of humidity on the rate of evaporation.
Answer:
Rate of evaporation decreases with the increase in humidity.
Explanation:

1. The amount of water present in air is called humidity.
2. The air around us cannot hold more than a definite amount of water vapour at a given temperature.
3. If the amount of water vapour is high in air, then the rate of evaporation decreases. Ex : Clothes dry slowly on a rainy day than on a normal day.

(c) Explain the effect of wind speed on rate of evaporation.
Answer:
Rate of evaporation increases with the increase in wind speed.
Explanation:

1. Because of increase in wind speed, particles of water vapour move away with the wind.
2. Due to this, amount of water vapour in the surroundings decreases.
3. It leads to increase in the rate of evaporation.
   Ex: Clothes dry faster on a windy day or under fan than a normal day.

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 11 Why Do We Fall Ill

AP State Syllabus 8th Class Biology Important Questions 10th Lesson Why Do We Fall Ill

8th Class Biology 10th Lesson Why Do We Fall Ill 1 Mark Important Questions and Answers

Question 1.
What is health?
Answer:
Health is a state of physical, mental and social well – being.

Question 2.
On what factors the health of an individual depends?
Answer:
The health of an individual is dependent on his or her physical surroundings and his / her economic status.

Question 3.
What is a disease ?
Answer:
Disease is actually self – explanatory. In other words, literally means being uncomfortable.

Question 4.
What is necessary for individual health ?
Answer:
Social equality and harmony are necessary for individual health.

Question 5.
What will happen if there is a disease ?
Answer:
When there is a disease, either the functioning or the appearance of one or more systems of the body will change for the worse.

Question 6.
What are acute diseases ?
Answer:
Some diseases last for only very short periods of time and these are called acute diseases.

Question 7.
What are chronic diseases ?
Answer:
Chronic diseases have very drastic, long – term effects on people’s health as compared to acute diseases.

Question 8.
What is the cause of a disease ?
Answer:
Lack of good nourishment may be the cause of a disease.

Question 9.
What are infectious diseases ?
Answer:
Diseases where microbes are the immediate causes are called infectious diseases.

Question 10.
Which bacteria is responsible for peptic ulcers ?
Answer:
Helicobacter pylori is responsible for peptic ulcers.

Question 11.
Name the organisms that cause diseases.
Answer:
Organisms that cause diseases are virus, bacteria, fungi, protozoans and worms.

Question 12.
Name the diseases caused by bacteria.
Answer:
Typhoid, cholera, tuberculosis and anthrax are caused by bacteria.

Question 13.
What diseases are caused by protozoans ?
Answer:
Protozoans cause malaria and kalaazar.

Question 14.
What are communicable diseases ?
Answer:
Diseases that spread from an infected person to other person by many microbial agents are called communicable diseases.

Question 15.
What is the function of our immune system ?
Answer:
In our body, the immune system fight and kill the disease causing organisms that enter into our body and defend us from diseases.

Question 16.
What are vectors ?
Answer:
Many diseases transmitted by other animals. These animals carry the infecting agents from a sick person to a healthy person. Such animals are called vectors. Ex: Mosquitoes.

Question 17.
Name the diseases caused by mosquitoes.
Answer:
Encephalitis or brain fever, filaria or elephantiasismalaria, dengue etc., are caused by mosquitoes.

Question 18.
Name the disease that causes physical contact.
Answer:
AIDS disease is caused by physical contact.

Question 19.
How do we kill microbes?
Answer:
By using antibacterial and anti – viral medicines we can kill microbes and also there are drugs that kill protozoa such as malarial parasite.

Question 20.
Why making anti – viral medicines is harder than making antibacterial medicines ?
Answer:
Because viruses have few biochemical mechanisms of their own.

Question 21.
What are infectious diseases?
Answer:
Diseases where microbes are the immediate causes are called infectious diseases.

Question 22.
What are symptoms?
Answer:
Some characteristic signs or indications that appear during sickness can help us to identify the sickness are called symptoms!

Question 23.
What is manifestation?
The appearance of the symptoms of a disease is called manifestation of the disease.

Question 24.
What is immunization?
Answer:
The creation of immunity usually against a particular disease, especially treatment by vaccination of an organism for the purpose of making it immune to a particular disease.

Question 25.
What are the different means by which infectious diseases are spread?
Answer:
Infectious diseases are spread through contaminated air, water, food and vectors like mosquitoes, flies, cockroaches, snails and even lies.

Question 26.
What are the vaccines available for preventing infectious diseases?
Answer:
There are vaccines against tetanus, diphtheria, whooping cough, measles, polio and many others.

Question 27.
Who discover vaccine for small pox for the first time?
Answer:
An English physician named Edward Jenner discovered vaccine forsmall pox for the first time.

Question 28.
Why are we normally advised to take bland and nourishing food when we are sick?
Answer:
When we fall sick our normal body functions will be affected and the digestion becomes slow, so it is advised to take bland and nourishing food.

Question 29.
What is needed to be healthy?
Answer:
Proper and sufficient nourishment and clean surroundings and food helps lis to be healthy.

Question 30.
Name the diseases that do not spread.
Answer:
Non – infectious diseases like cancer, high blood pressure do not spread.

8th Class Biology 10th Lesson Why Do We Fall Ill 2 Marks Important Questions and Answers

Question 1.
What are the diseases caused by bacteria in Man?
Answer:

1. Cholera
2. Typhoid
3. Diptheria
4. Whooping cough
5. Tetanus
6. Tuberculosis
7. Leprosy

Question 2.
Name the diseases caused by viruses in man.
Answer:

1. Small pox
2. Chicken pox
3. Measles
4. Mumps
5. Poliomelitis

Question 3.
What are the diseases caused by Protozoans in Man?
Answer:

1. Malaria
2. Kala Azar
3. Amoebic Desentry

8th Class Biology 10th Lesson Why Do We Fall Ill 4 Marks Important Questions and Answers

Question 1.
Draw the picture of SARS VIRUS in your scrap book and write the size of SARS VIRUS.
Answer:
Picture of SARS VIRUS

The size of SARS VIRUS is 500 nano metres, which is half a micrometre, which is one thousandth of a millimetre.

Question 2.
Draw the picture of staphylococci bacteria. In what way it affect the health of people?
Answer:
Staphylococci Bacteria

Staphylocoecci bacteria cause acne.

Question 3.
Draw a picture showing an adult round worm and answer the given questions:
a) What is the scientific name of round worm?
b) Where does it live in human beings?
Answer:
Round Worm

a) The Scientific name of Round Worm is Ascaris lumbricoides.
b) It stays in the small intestine of human beings.

Question 4.
Draw a picture showing the air borne diseases will spread in the air.
Answer:
Spread of air borne diseases

Question 5.
Draw a flow chart which shows common methods of transmission of diseases. How the animals transmit diseases? Explain.
Answer:

We lie in an environment that is full of many other creatures apart from us. It is inevitable that many diseases will be transmitted by other animals.
These animals carry the infecting agents from a sick person to another potential host. These animals are intermediates and are called vectors.
The commonest vectors are mosquitoes. The female mosquitoes need highly nutri¬tious food in the form of blood in order to be able to lay mature eggs. In this way they can transfer diseases from person to person.

Question 6.
How does death occurs in AIDS patients?
Answer:

1. In HIV infection, the virus goes to the immune system and damage its function.
2. The body can no longer fight off with even minor infections.
3. Even mild cold becomes Pneumonia. Thus ultimately these infections kill the people suffering from HIV – AIDS.

8th Class Biology 10th Lesson Why Do We Fall Ill Important Questions and Answers

Question 1.
Prepare a pamphlet to aware people to maintain a hygienic surrounding.
Answer:
Pamphlet
“Prevention is better than cure”. So, it is better for us to prevent diseases rather than treatment. You should keep our surroundings clean and hygienic wash your hands with soap or handwash lotion thoroughly before consuming food. Wash your hands with soap after defecation. You should consume your food only when it is hot. Do exercises daily to keep you fit and healthy. Try to cultivate good habits which keep you healthy always. Use mosquito nets to avoid mosquito bites.
“SWACH BHARAT – SWASTH BHARAT”.

AP State Syllabus AP Board 8th Class Biology Solutions Chapter 11 Why Do We Fall Ill Textbook Questions and Answers.

AP State Syllabus 8th Class Biology Solutions 11th Lesson Why Do We Fall Ill

8th Class Biology 11th Lesson Why Do We Fall Ill Textbook Questions and Answers

Improve Your Learning

Question 1.
A doctor/nurse/health-worker is exposed to more sick people than others in the community. Find out how she/he avoids getting sick herself/himself.
Answer:

1. By choosing nutritious food and an active lifestyle, managing stress, using tobacco- free, getting preventive immunizations and screenings and choosing protection measures.
2. Maintaining good hygiene:
   By washing hands frequently, cleaning their stethoscopes from patient to patient, using gloves.
3. Recognising the symptoms quicker and knowing what to do can help speedy recovery, easier access to medical care. (E.g.: They can self-prescribe, can ask col¬leagues for help etc.)

Question 2.
Differentiate the infective and non-infective diseases.
Answer:

1. Infectious diseases can be spread from person to person.
   Non-infectious diseases can not be spread from person to person.
2. Infectious diseases are caused by pathogens (microbes) which are disease causing organisms.
   The major group of pathogens (microbes) are viruses, bacteria, fungi, single cell organisms like protozoans, multicellular organisms like worms.
   Non-infectious diseases are not caused by Pathogens (microbes), but can be caused by physiological malfunctions, environmental or chemical factors, heredity, unknown causes. These are mostly internal, non-infectious causes.
3. Examples of infectious diseases are Viral, diseases, bacterial etc.
   Example for non infectious causes are some cancers caused by genetic abnormali¬ties and high blood pressure caused by excessive weight and lack of exercise.

Question 3.
Why acute disease become chronic disease?
Answer:

1. Some diseases last for only very short periods of time and these are called acute diseases.
   E.g.: Common Cold lasts only a few days.
2. Some other diseases or ailments can last for a long time, even as much as a life time and are called chronic diseases.
   E.g,: The infection causing elephantiasis, which is very common in some parts of India.
3. As an example, a cough and cold which all of us have from time to time. Most of us get better and become well within a week or so.
4. But if we get infected a chronic disease like tuberculosis of the lungs, it takes over the years to suffer with cough and lose weight and feel tired all the time.
5. In other words, we are likely to have prolonged general poor health if we have a chronic disease.
6. Chronic diseases therefore have very drastic, longterm effects on people’s health
   as compared to acute disease.
7. One reason might be that, because the person is not well nourished and does not get enough food and it is because of poverty, the acute disease becomes a chronic disease.

Question 4.
Draw the figure of leishmania and trypanosome.
Answer:

Question 5.
Ramu was effected with small pox. What advice do you give Ramu for not spreading disease?
Answer:
Prevention of Small Pox:

1. Isolation of the infected person.
2. Surrounding should be kept clean and hygeinic.
3. Clothes of the infected person must be washed in hot water and dried in the Sun.
4. They should not be used by others.
5. Small Pox can be prevented by taking vaccine against it.
6. But in 1776 Edward Jenner discovered a vaccine for small pox. Now it is wiped out from our country.

Question 6.
How do you appreciate for role of vaccine in preventing disease?
Answer:

1. Vaccination was discovered by a British doctor called Edward Jenner in the year 1776. Since then, this method has been modified and has become most popular for making people resistant to disease.
2. In this process, the disease causing organism are cultured in the laboratory and are collected. They are killed by heat treatment.
3. The dead micro-organisms are made into a suspension and injected into humans. The body reacts to these dead micro-organisms as if they are alive and are produces antibodies.
4. Next time when the same disease producing micro-organisms enter the body, these antibodies will react and kill them.
5. Thus the person is not affected by the disease, even if he is exposed to the disease causing microorganisms. Vaccination also prevents the spread of epidemics.
6. At present, vaccines are available for various diseases-Cholera, typhoid, diphtheria, whooping cough, polio, tuberculosis etc. Some of the vaccines if taken once, the immunity persists for life time, while in some cases the immunity will lasts only for limited amount of time.

Question 7.
Prepare a questionnaire to collect the information from your local health worker about spreading of diseases?
Answer:

1. What are the causes for a disease?
2. Name the organisms that cause diseases.
3. Name the diseases caused by virus, bacteria, fungi and protozoans.
4. How the infectious agents spread?
5. Name the diseases caused by air, water and physical contact.
6. What are the symptoms of Typhoid and Jaundice?
7. How can we prevent exposure to infectious diseases?
8. How do we kill microbes?
9. How to get rid of an infection in some one who has the disease?
10. What are the treatments for any type of diseases?
11. What are the measures taken by Public Health,Programmes to prevent diseases?
12. What is immunization? What are antibiotics?
13. What is the duty of everyone in the community for the effective prevention of infectious diseases?

Question 8.
How many times did you fall ill in the last one year? What were the illnesses?
a) Think of one change you could make in your habits in order to avoid any of/ most of the above illnesses.
b) Think of one change you would wish for in your surroundings in order to avoid any of/most of the above illnesses.
Answer:
In the last one year, fall ill for one time with Malaria.
Symptoms:

1. It is a communicable disease caused by the Protozoan Plasmodium Falciparum. It is spread by the infected female anopheles mosquito.
2. It starts with extreme cold. Patient wants to be covered with heavy blankets. This is followed by fever, as high as 106° F.
3. There will be severe head ache and body pains. There will be sweating.
4. In children the parasite enter and block the capillaries, supplying blood to the brain. The blood vessels may ruptures child becomes unconscious and may even die.

a) Think of one change you could make in your habits in order to avoid any of/ most of the above illnesses.
Answer:
Preventive measures of malaria:

1. To reduce the mosquito population successfully.
2. By protecting ourselves from mosquito bites, the spread of malaria can also be prevented.
3. Best method is to use mosquito nets while sleeping and by using mosquito proof nets for windows and doors. These nets do not allow mosquitoes to enter the house.

b) Think of one change you would wish for in your surroundings in order to avoid any of/most of the above illnesses.
Answer:

1. Preventing water stagnation in water tanks, drainage canals, and discarded vessels lying outside. The stored water tanks should be emptied frequently and filled with fresh water.
2. Spraying of insecticides or light oil such as kerosene on stagnant water, especially in drainage water.
3. Growing of specific varieties of fishes in stagnant water. They feed on mosquito larvae.

Question 9.
Conduct a survey in your neighbourhood to find out what the three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.
Answer:
The most common cause for the spread of diseases in our neighbourhood is by drinking of contaminated water. Polio, Cholera, Typhoid, Jaundice and Amoebiasis and several worms spread through drinking water.
Preventive Measures:

1. Drinking water is purified by filtration and chlorination before it is supplied through municipal taps and provide safe drinking water.
2. Providing basic sanitation by keeping the surroundings clean.
3. Arranging the public health programmes to prevent and control of local diseases by giving immunisation to childhood.

8th Class Biology 11th Lesson Why Do We Fall Ill InText Questions and Answers

Question 1.
Let us read the wall writings on the panchayat office

Drink boiled water only.
Use mosquito nets.
Keep your surroundings neat and clean.
Do not left water to stagnate.
Eat food when it is hot.
Wash hands before eating food.
Wash hands after toilet.
Use toilets only, not defecate in open.
Keep lids on food vessels.
Wash vegatables before cooking

a) Why local Panchayats display such instructions on the wall?
Answer:
To bring awareness in the local people against diseases.

b) What do we come to know from such instructions?
Answer:
Such infections will spoil the health of people.

c) What would happen if we do not follow the instructions.
Answer:
People who would not follow the instruction may fall sick.

d) In which season do we generally find more mosquitoes? How do they affect us?
Answer:
Generally we find more mosquitoes in rainy season. Mosquitoes cause malaria.

e) What is health ? And when do we fall sick?
Answer:
Health is a state of being well enough to function physically, mentally and socially with optimum efficiency.
When disease causing organisms attack us we fall sick.

Question 2.
State any two conditions essential for good health.
Answer:
Clean surroundings and fresh air.

Question 3.
State any two conditions essential for being free of disease.
Answer:
Safety food and water and exercise to the body.

Question 4.
Are the answers to the above questions necessarily the same or different? Why?
Answer:
Different.

Question 5.
Do all diseases spread to people coming in contact with a sick person?
Answer:
No, some diseases are infectious and some diseases are non-infectious.

Question 6.
What are the diseases that are not spreading?
Answer:
Non-infectious diseases E.g.: Some cancers, high blood pressure etc.

Question 7.
How would a person develop those diseases that do not spread by contact with a sick person?
Answer:
Non-infectious diseases are some times caused by genetic abnormalities, excessive weight or lack of exercise.

Question 8.
List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?
Answer:
Because of not feeling well, unable to do daily work and when feeling uneasy thinking that we are sick we want to see the doctor. If the situation is unbearable then we would like to see the doctor.

Question 9.
In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?
Answer:

1. If in the case of Jaundice, the suffering will be more and it will be cured only by taking medicines. Prescribed by a doctor.
2. Because this is the disease for liver, the normal functioning of the liver will be stopped, and feels unpleasant.

8th Class Biology 11th Lesson Why Do We Fall Ill Activities

Activity – 1

Question 1.
a) Find out what provisions are made by your local authority (Panchayat/ Municipal Corporation) for the supply of clean drinking water.
Answer:
The Panchayat/Municipal Corporation should filter the water and chlorinated before sending through pipes.

b) Are all the people in your locality able to access this?
Answer:
Yes, all the people can access this. The people are avail of this.

Activity – 2

Question 2.
a) Find out how your local authority manages the solid waste generated in your neighbourhood.
Answer:
The solid waste generated in the neighbourhood is collected and disposed.

b) Are these measures adequate?
Answer:
Yes. But still more they can take measures.

c) If not what improvement would you suggest?
Answer:
The authority can announce the public to reduce the waste in the household.
Suitable arrangements will be arranged for the garbage disposal, to prevent accumulation of waste in and around residential areas. This attracts the houseflies and other microbes to spread diseases.

d) What could your family do to reduce the amount of solid waste generated during a day/week from your house?
Answer:
The peels of fruits and vegetables and other waste materials which decay and turns good manure can deposit in the compost pit.

Activity – 3

Question 3.
Survey your neighbourhood to find out:
a) How many people did suffer from acute diseases during the last three months?
Answer:
More people suffered from acute diseases.

b) How many people did develop chronic diseases during this same period?
Answer:
Very few people develop chronic diseases.

c) And finally, what is the total number of people suffering from chronic diseases in your neighbourhood?
Answer:
One or two.

d) Are these answers to questions (I) and (2) different?
Answer:
Same.

e) Are these answers to questions (2) and (3) different?
Answer:
Same.

f) What do you think could be the reason for these differences? What do you think would be the effect of these differences on the general health of the population?
Answer:
In general people get acute diseases seasonally but chronic diseases are drastic, long term effect because of their poor health.

Activity – 4

Question 4.
a) Find out how many of in your class had cold/cough/fever recently.
Answer:
One or two or few students.

b) How long did the illness last?
Answer:
The illness lasts for one week.

c) How many of you took antibiotics?
Answer:
Half of the students took antibiotics.

d) How long did they suffer who took antibiotics pills?
Answer:
Seven days.

e) How long did they suffer who did not take antibiotics pills?
Answer:
Seven days.

f) Is there any difference between these two groups?
Answer:
No difference is seen between these two groups.

g) If yes, why ? If not, why not?
Answer:
Because antibiotics do not work against viral infections.

Activity – 5

Question 5.
Conduct a survey in your locality. Talk to ten families who are well-off and ten who are very poor. Both sets of families should have children who are below five years of age. Measure the heights of these children. Draw a graph of the height of each child against its age for both sets of families.
Families who are well – off

Families of very poor

a) Is there any difference between the groups? If yes, Why?
Answer:
Yes, there is a difference between the groups. The children who are sufficient nourishment have good health. Their growth is healthy.

b) If there is no difference, do you think that your findings mean that being well-off or poor does not matter tor health?
Answer:
The functioning of the immune system, like any other system in the body, will not be good if proper and sufficient nourishment and food is not available.
So the availability of proper and sufficient food helps us to be healthy.

Activity – 6

Question 6.
Rabies virus is spread by the bite of infected dogs and other animals. There are anti-rabies vaccines for both humans and animals.
a) Find out the plan of your local authority for the control of rabies in your neighbourhood.
Answer:
Control of Rabies:

1. Parental rabies vaccination of owned dogs.
2. Sterlization of pet dogs.
3. Unwanted dogs should not be abondoned.
4. Animal birth control attempt should be made to sterilize the stray dog population or other methods of birth control should be investigated.
5. Suitable infrastructure for garbage disposal, to prevent the accumulation of waste in and around residential areas.

This attracts stray and ownerless dog packs to these areas.
Vaccination:
Sufficient and affordable cell culture vaccine should be available for post exposure treatment.
Mass oral vaccination of the stray dog population.

b) Why we are normally advised to take bland and nourishing food when we are sick?
Answer:
When we fall sick our normal body functions will be affected the digestion will be slow, so it is advised to take bland and nourishing food when we are sick.

c) What are the different means by which infectious diseases are spread?
Answer:
The infectious diseases are spread through contaminated air, water, food and vectors like mosquitoes, flies, cockroaches, snails and even lice.

d) What precautions can you take in your school to reduce the incidence of infec-tious diseases?
Answer:

1. Encouraging sick students and staff to stay at home and seek medical attention for several illnesses.
2. Facilitating hand hygiene by supplying soap and paper towels and teaching good hand hygiene practicles.
3. Cleaning of class room materials and surfaces.
4. Daily announcements about preventing infectious diseases.
5. Encouraging students and staff to get annual influenza vaccination.

e) What is immunization?
Answer:
The creation of immunity against a particular disease, by vaccination of an organism for the purpose of making it immune to a particular pathogen (disease causing organ¬ism) is called immunisation.

f) What are the immunization programmes available at the nearest health centre in your locality?
Answer:
More children are being protected against vaccine preventable diseases, such as tuberculosis tetanus, pertusis (Whooping cough), diphtheria, polio, measles and now hepatitis – A, B then ever before.
The public health programme of childhood immunisation for preventing infectious diseases.

g) Which of these diseases are the major health problems in your area?
Answer:
Measles and jaundice.

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 6 Sound

AP State Syllabus 8th Class Physical Science Important Questions 6th Lesson Sound

8th Class Physical Science 6th Lesson Sound 1 Mark Important Questions and Answers

Question 1.
What is sound? How does sound produces?
Answer:
Sound is a form of energy. A vibrating body produces sound.

Question 2.
Honeybee produce peculiar sound through their mouth or some other organ used for that purpose?
Answer:
A honeybee can’t make a sound using vocal cords. The buzzing sound that you b*ear from any flying insect is caused by vibration of their wings when flying.

Question 3.
Length of vocal cords in men is nearly 20 mm, in women it is about 5 cir1 less. Whereas in children it is shorter. Can we say that the length of vocal cords plays any role in deciding the quality of sound produced by men, women and children?
Answer:
Yes, we can say that the length of vocal cords decreases then the shrillness °f sound increases.

Question 4.
Pitch of the voices of the following is in ascending order. Lion < adult man < adult woman < child < infant < insect. Can you guess the reason why?
Answer:
The pitch of the voices depend on frequency. As the number of vibrations per second increases the pitch or shrillness increases. So insect produce shrillness due to more frequency of vibration.

Question 5.
Do you find any difference in blowing the whistle and striking the drum?
Answer:
Whistle has more shrillness due to its higher frequency than drum which has less frequency.

Question 6.
Why are some sounds loud?
Answer:
The sounds which have greater amplitude are louder.

Question 7.
Why are some sounds feeble?
Answer:
The sounds which have low amplitude are feeble.

Question 8.
Is there any relation between the intensity of sound and vibrations of the body which produces sound?
Answer:
As amplitude of vibration increases the intensity of sound increases.

Question 9.
How many times is a car horn more powerful than near total silence?
Answer:
It is 10¹¹ times more powerful than a near total silence.

Question 10.
How many times is a jet engine more powerful than a smallest audible sound?
Answer:
It is 10¹² times more powerful than a smallest audible sound.

Question 11.
What is a vibration?
Answer:
The to and fro motion of a body from its mean position is known as vibration.

Question 12.
What is amplitude?
Answer:
The maximum displacement of vibrating body from its mean position is called amplitude.

Question 13.
What are the parts of the speech organ which involved in producing sounds?
Answer:

1. Vocal cords
2. Lips
3. Teeth and tongue
4. Nose and throat

Question 14.
What is a music?
Answer:
Music is a combination of sounds that are produced in an order and pleasant to hear.

Question 15.
What is a noise?
Answer:
The sounds which are not pleasant to hear is called a noise.

Question 16.
What is pitch?
Answer:
The shrillness of a sound is known as pitch.

Question 17.
What is frequency?
Answer:
The number of vibrations per second is called frequency.

Question 18.
What is audible sounds? What is audible range?
Answer:
The sounds that a normal human being can hear is called audible sounds. Frequency of audible sound ranges from 20 cycles / second to 20000 cycles / second.

Question 19.
Do we hear the sounds produced by bats?
Answer:
We cannot hear sounds produced by bats because the sounds produced by bats have frequency more than 20,000 cycles / seconds that is more than audible range.

Question 20.
Does the sound travel if there is no medium?
Answer:
Sound required medium for its propagation. So sound does not travel if there is no medium i.e vacuum.

Question 21.
A bird makes high pitch sound and a lion makes a low pitch roar. Which one produce sound of more frequency?
Answer:
The bird produces sound of more frequency because it has high frequnecy as we already know pitch depends upon frequency.

Question 22.
Why do we produce sounds with different pitches or amplitudes while speaking?
Answer:
The vibration in pitch and amplitude of sound during our speech helps us to communicate with others in form of language.

Question 23.
Lightning and thunder take place in the sky at the same time at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
Answer:
The speed of light is more than speed of sound so light travels faster. So we can see lightning first then we can hear thunder.

Question 24.
How intensity of sound related to its unit?
Answer:
The smallest audible sound (nearer to total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful that of total silence is 20 dB. A sound 1000 times more powerful than sound nearer to silence is 30 dB.

Question 25.
How many times is a jet engine more powerful than the whispering sound?
Answer:
The decibel rating of jet engine = 120 dB
The decibel rating of whisper = 20 dB (for practical purpose)
The number of times a jet engine more powerful than a whisper = 10¹⁰ times
{120 – 20 = 100 that is taken as 10¹⁰}

Question 26.
How do you feel when you hear sounds in busy traffic?
Answer:
It is very unpleasant to hear.

Question 27.
How do you feel while listening to songs from a radio?
Answer:
It is very pleasant to hear.

Question 28.
Which of the above sounds are more pleasant to hear?
Answer:
Songs from radio are more pleasant to hear.

Question 29.
What is the unit to measure the sound intensity?
Answer:
Decibel is the unit for measuring the intensity of sound. It is denoted as dB.

8th Class Physical Science 6th Lesson Sound 2 Marks Important Questions and Answers

Question 1.
What is sound pollution? What are the causes of sound pollution?
Answer:
The unwanted sound in our surroundings is called sound pollution.
Causes of sound pollution:

1. Sounds of traffic
2. Sounds by motor bikes and their horns
3. Sounds in construction sites
4. Sounds at industries
5. Sounds at mines
6. Sounds during explosions and bursting of crackers
7. Sounds from mixer/grinder, washing machines and motors, etc.

Question 2.
Write some common sounds and their decibel ratings.
Answer:
Near total silence – 0 dB
A whisper – 15 dB
Normal conversation – 60 dB
A lawn mower – 90 dB
A car horn – 110 dB
A jet engine – 120 dB
A gun shot or fire cracker – 140 dB

Question 3.
How many times is a car horn more powerful than normal conversation?
Answer:
The decibel rating of car horn = 110 dB
The decibel rating of normal conversation = 60 dB
The number of times a car horn more powerful than normal conversation = 10⁵ times
{110 – 60 = 50 which is taken as 10⁵} (The explanation beyond our syllabus. It is based on logarithms)

Question 4.
How can you explain the sound has energy?
Answer:
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 sand particles on the balloon diaphragm and observe the movement of particles. Do the same activity after removing the phone from the bottle. Sound has energy

Question 5.
What are the differences between the noise and music? Explain.
Answer:

Question 6.
Explain the sources which produce sound pollution in your surroundings.
Answer:
Sources of sounds that are produce to sound pollution:

1. Sounds in traffic
2. Sounds by motor vehicles
3. Sounds in construction sites
4. Sounds in industries
5. Sounds in mines
6. Sources of sound pollution like mixer, grinder, washing machines and motors, etc.

Question 7.
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.
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.

Question 8.
Why the voice of men, women and children are different?
Answer:
The vocal cords of men about 20 mm long. In women these cords are about 5 mm shorter in respect to men. Children have very short vocal cords. That is the reason that voice of men, women and children are different.

Question 9.
On which property of vibrations does the loudness of sound depend?
Answer:
The loudness of sound is determined by its amplitude. When the amplitude of a vibration is large, the sound produced is loud. When the amplitude is small, the sound produced is feeble.

Question 10.
What are the harmful effects of noise pollution?
Answer:

1. Presence of excessive noise in the surroundings may cause many health related problems.
2. Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorder may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temperory or even permanent deafness.

Question 11.
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.
Answer:
In the winter season the air has fogs and behaves as liquid medium. So, the air moves little faster in it. Whereas in the summer the air is dried and no possibility of droplets. Hence the sound moves slower.
The propagation of sound is Solids > liquids > gases

Question 12.
Define audible sounds and inaudible sounds.
Answer:
Audible sounds:
The sounds that a normal human being can listen are called audible sounds. Frequency range is 20 cycles/sec – 20000 cycles/sec.
Inaudible sounds:
The sounds that a normal human being can’t listen are called inaudible sounds. Frequency range is less than 20 cycles/sec. or greater than 20000 cycles/sec.

8th Class Physical Science 6th Lesson Sound 4 Marks Important Questions and Answers

Question 1.
Describe structure of larynx or voice box.
Answer:
Larynx is the important organ in human body to produce sound. It has two muscular ligaments at the end of wind pipe called vocal cords. They are stretched across voice box, it leads to a narrow slit between them, to allow passage of air.

Vocal cords open during breathing to allow air into lungs. Vocal cords close when we speak.
The air from the lungs presses between them to use vibration and produce sound.

Question 2.
Draw anatomy of the larynx and label its parts.
Answer:

Question 3.
Draw the figures of using three musical instruments in your surroundings.
Answer:

Question 4.
a) Can sound travel in vacuum? Explain.
b) In which medium sound travels much faster and slower? Give some examples.
Answer:
a) Sound can’t travel in vacuum as it needs particles for propagation. As vacuum is empty, it is not possible.
b) Sound travels much faster in solids as the particles in solids are very closely packed, e.g.: Sound travels in train tracks (Railway tracks).
Sound travels much slower in gases as the particles in gases (air) are very loosely packed.
e.g.: Thunder or sound produced from amplifier at a long distance is feeble to hear.

Question 5.
Which object is vibrating when the following sounds are produced?
i) The sound of sitar or veena
ii) The sound of tabla
iii) The buzzing of bee or a mosquito
iv) The sound of a school bell
v) The sound of bursting balloon
vi) The radio
Answer:
i) Strings of sitar or veena vibrate to produce sound.
ii) The skin of the tabla vibrate to produce sound.
iii) Wings of mosquito or a bee vibrate to produce sound.
iv) The disc of the bell when beated with hammer vibrate to produce sound.
v) Air vibrates to produce sound.
vi) In the radio speakers vibrate to produce sound.

Question 6.
On which property of vibrations determines the pitch of the sound? Explain with examples.
Answer:

1. The frequency determines the shrillness or pitch of sound.
2. If the frequency of vibration is higher we say that the sound has a higher pitch.
3. If the frequency of vibration is lower, we say that the sound has a lower pitch. For example, the drum vibrates with a low frequency. Therefore, it produces a low pitched sound:
4. On the other hand, a wristle has a higher frequency, and therefore produces a sound of higher pitch.
5. A bird makes a high pitched sound whereas a lion makes a low pitch roar.

Question 7.
How can the noise pollution be controlled in a residential area?
Answer:

1. The noisy operations must be conducted away from any residential area.
2. Noise producing industries should be set up away from such areas.
3. Use of automobile horns are minimized.
4. T.V and music systems should be run at lower volumes.
5. Plants must be planted along the roads and around buildings to minimize the harmful effects of noise pollution.

Question 8.
What is the audiable range of frequencies for human beings? Explain.
Answer:

1. Sound of frequencies less than about 20 vibrations per second (20 Hz) cannot be detected by the human ear.
2. Such sounds are called inaudible.
3. On the other side, sound of frequencies more than about 20,000 vibrations per second (20,000 Hz) are also not audible to the human ears.
4. Thus for human ears, the range of audible frequencies is roughly between 20 to 20,000 Hz.

Question 9.
What is eardrum? How does it play an important role in hearings?
Answer:

1. We hear sound through our ears.
2. The shape of the outer part of ear is like a funnel.
3. When sound enters in it, it travels down a canal at the end of which a thin membrane is stritched tightly.
4. It is called the eardrum.
5. It performs an important function.

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

Question 1.
Majority of communication in human beings is through speech. Name the organs which give human beings the ability to talk.
Answer:

1. Vocal cords
2. Lips
3. Teeth and tongue
4. Nose and throat

Question 2.
Why our steps do not produce sound if we walk on a carpet floor?
Answer:
Carpets are soft and as we know soft materials are bad conductors of sound. Thus the
carpet tends to absorb the sound produced. Also when we walk on the carpet the amplitude and vibrations of the floor is reduced leading to a lesser sound.

Question 3.
Sound does NOT travel in vacuum. Explain why.
Answer:

1. Sound energy travels in the form of wave.
2. To produce waves medium is required.
3. Hence, if there is no medium, sound waves cannot form.

Question 4.
Complete the following table.

Answer:

Question 5.
Mention the sounds which are responsible for sound pollution. Suggest four controlling measures of sound pollution.
Answer:
Causes of sound pollution:

1. Sounds of traffic
2. Sounds by motor bikes and their horns
3. Sounds in construction sites
4. Sounds at industries
5. Sounds at mines
6. Sounds during explosions and bursting of crackers
7. Sounds from mixer / grinder, washing machines and motors etc.

The steps to reduce sound pollution :

1. Attach silencers to the bikes and other machines to reduce sound.
2. Manufacture machines that work with lesser noise.
3. During the use of TVs and taperecorders tune down volume of sound.
4. Plant trees to reduce sound pollution.

Question 6.
What is sound pollution? Write effects of sound pollution. Suggest some measures to control sould pollution.
Answer:
The unwanted sound in our surroundings is called sound pollution.
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.

The steps to reduce sound pollution :

1. Attach silencers to the bikes and other machines to reduce sound.
2. Manufacture machines that work with lesser noise.
3. During the use of TVs and taperecorders tune down volume of sound.
4. Plant trees to reduce sound pollution.

Question 7.
Kushwanth said “Vibrating objects produce sound.” Establish that the given statement is true with relevant example from your surroundings.
Answer:
The statement given by Kushwanth is correct.
That is “vibrating objects produce sound”.
1. Eg: 1) If we ring the bell in the school, sound will produce.
2) If we touch the bell while ringing, vibrations will experience.

2. Eg: 1) We can observe sound coming from the engine of a vehicle.
2) This is due to vibration of the engine.

3. Eg: 1) Musical instruments vibrates and produce sound.
2) If we pull the string of a veena or guitar.
3) It will produce sound.

Question 8.
Based on the below information answer the following questions.

a) Name the instruments which have vibrating part like a thin elastic rubber band.
Answer:
Tabla, Dholak, Drum.

b) What are the vibrating particles in the air column?
Answer:
Air particles.

c) What is the difference between Tabla and Sitar in terms of how they produce sound?
Answer:
In Tabla, stretched membrane vibrates and produce sound. Whereas in Sitar stretching string vibrates and produce sound.

d) How to produce different frequencies using a flute?
Answer:
By closing holes of the flute with fingers (or) By changing length of the air column.

Question 9.
Write about the propagation of sound in different media.
Answer:

1. Sound produced by source travels in a medium in the form of waves.
2. Vibrations produced by source of sound travel by particles of medium.
3. In the case of solids, particles of solid substance vibrates and travel along the substance.
4. In the case liquids, molecules of liquids carry the vibrations for sound propagation.
5. In the case of gas, gaseous molecules act as carries of vibrations and allow the sound propagation.

Question 10.
Explain the structure and functions of the ear using a diagram.
(OR)
Describe briefly about structure and functioning of the eardrum.
Answer:
Our ear consists of three sections, the outer ear, the middle ear and the inner ear, Pinna of external ear collects the sound vibrations. They enter into the ear canal. We have learnt that sound travels in the form of vibrations: These vibrations strike the tympanum (eardrum) and make it to vibrate.

The vibrations from the tympanic membrane reach the middle ear (ear ossicles), contains three small bones malleus (hammer shaped), incus (anvil shaped) and stapes (stirrup shaped). They magnify the sound vibrations.
The stapes transmits the vibrations to the membrane of oval window. The oval window has the surface area 1/20th of the ear-drum. By this the vibrations increase 30 to 60 times. The vibrations from the oval window transmit to the cochlea which is the inner part of the ear. The cochlea is filled with fluid which transmits the vibrations. The motion of the vibrations in the cochlea is detected by tiny hairs connected to nerves at this point. The vibrations are transformed into electrical signals and carried by the nerves to the brain where the sensation of the sound is realized.

AP State Syllabus AP Board 8th Class Biology Important Questions Chapter 5 Attaining the Age of Adolescence

AP State Syllabus 8th Class Biology Important Questions 5th Lesson Attaining the Age of Adolescence

8th Class Biology 5th Lesson Attaining the Age of Adolescence 1 Mark Important Questions and Answers

Question 1.
What is adolescence period ?
Answer:
The age between 13-19 years is called adolescence.

Question 2.
In which period growth takes place?
Answer:
Growth takes place in adolescence period.

Question 3.
When does growth in height stop?
Answer:
Growth stops in boys at the age of 18, in girls at the age of 17.

Question 4.
Who do grow faster?
Answer:
Girls grow faster than the boys.

Question 5.
What is Adam’s apple?
Answer:
A partial growth of larynx.

Question 6.
Why is the Adam’s apple formed?
Answer:
The Adam’s apple is formed due to elongation of the thyroid cartilage, which protrudes out in front of the neck.

Question 7.
Name the secondary sexual characters in boys.
Answer:
Facial hair, moustaches and beard.

Question 8.
What are primary sexual characters?
Answer:
The sex organs by which children are identified as boys and girls at birth represent primary sexual characters.

Question 9.
What is reproduction?
Answer:
Reproduction is the most important process for continuation of human race.

Question 10.
What is the age for the production of gametes?
Answer:
Mostly in between 11-15 years.

Question 11.
What is menarche?
Answer:
The first menstrual cycle begins at adolescence and is termed as menarche.

Question 12.
What is menopause?
Answer:
At 45 – 50 years of age, the menstrual cycle stops. This is termed as menopause.

Question 13.
When does menstruation occur?
Answer:
Menstruation occurs once in about 28 – 30 days.

Question 14.
What is child marriage?
Answer:
Child marriage is a social evil which causes unwanted damage to the lives of children.

Question 15.
What is the legal age for marriage?
Answer:
The legal age for marriage is 18 years for girls and 21 years for boys.

Question 16.
What is the first and foremost duty of every adult?
Answer:
The first and foremost duty of every adult is to prepare oneself to reveal to the adolescent the secretes of nature and the natural course of life as it is Adolescent queries must never go unwanted.

Question 17.
What is the function of endocrine glands?
Answer:
They help in the regulation of the functioning of the human body.

Question 18.
What do endocrine glands release?
Answer:
They release some chemicals (called hormones) directly into the blood.

Question 19.
What is the other name for endocrine glands?
Answer:
Ductless glands as they do not have ducts.

Question 20.
What is the name of the male hormone?
Answer:
The male hormone is ‘Testosterone’.

Question 21.
What is the hormone begin to produce in girls?
Answer:
In girls, the female hormone ‘estrogen’ begins to produce in adolescence.

Question 22.
What is the name of the milk secreting glands?
Answer:
Mammary glands.

Question 23.
Which hormone controls emotions?
Answer:
Adrenalin hormone secreted by Adrenal gland.

Question 24.
Why do the hunger levels are high in adolescents?
Answer:
At this stage there is rapid growth and development.

Question 25.
How do young boys and girls keep the body fit and healthy?
Answer:
All young boys and girls should take a walk, exercise and play outdoor games.

Question 26.
Why are endocrine glands called ductless glands? Name them.
Answer:
Since they do not have specialized ducts, endocrine glands are called ductless glands. Ex : Pituitary gland, Thyroid gland, Adrenal gland etc.

Question 27.
Why do adolescents generally prefer to eat chips, snacks etc?
Answer:
The growth rate in adolescents is in high rate. Because of this reason they feel hungry and they prefer to eat chips, snacks etc.

Question 28.
Why is it not good to eat junk foods?
Answer:
Eating junk foods regularly may cause problems like obesity, mouth and stomach ulcerations, increase in blood sugar levels and blood pressure etc. So adolescents must say no to junk foods.

Question 29.
What are the factors involved in, to reach proper height?
Answer:
It is influenced primarily by heredity and also environmental factors such as proper nurishment and regular exercise.

Question 30.
Nowadays reaching age of adolescence in girls become reduced – support your answer.
Answer:
Nowadays reaching age of adolescence in girls become reduced . Some observations explain that it is because of polluted food materials such as estrogen present milk. This fact may also effect the boys and delay the reach of reproductive phase.

Question 31.
What is a balanced diet?
Answer:
The diet which includes proteins,carbohydrates, fats and vitamins in require proportions is called a balanced diet.

8th Class Biology 5th Lesson Attaining the Age of Adolescence 2 Marks Important Questions and Answers

Question 1.
What is menstrual cycle? When does it begin? What happens during this period?
Answer:
Menstrual cycle:

1. The cycle of changes takes place in the female reproductive system is called menstrual cycle. It occurs once in 28 to 30 days.
2. It is termed as “menarche”.
3. The first menstrual cycle begins at around 10-12 years of age and lasts till the age of 45 – 50 years.

Question 2.
Why is child marriage a social sin? Give reason.
Answer:

1. As per child marriage restriant act 1978, the maximum age for marriage is 21 years for females and 23 years for males.
2. A female whose age is less than 21 years is not physically or mentally developed.
3. Because of anatomical immaturity, she is not in a condition to either to lead a married life or to have children.
4. Marriage at lower age for girls becomes a greater risk both for the girl and the child.
5. Hence child marriage is a social sin, it should be avoided.

Question 3.
What are endocrine glands? What do they release?
Answer:
Endocrine Glands:

1. The glands which help in the regulation of the functioning of the human body are called endocrine glands.
2. They release some chemicals directly into the blood which are called hormones.

Question 4.
What are the functions of Endocrine hormones?
Answer:
Functions of Endocrine Hormones:

1. They control the sugar levels, salt and sodium levels in the blood.
2. They control water levels of the body.
3. They play an important role in development of the reproductive system.
4. The hormones control the physical changes during adolescence, puberty, pregnancy, menopause etc.

Question 5.
How is physical exercise good for young boys and girls?
Answer:

1. Walking and playing in fresh air keeps the body fit and healthy.
2. All young boys and girls should take a walk, exercise and play out door games.
3. The physical activity leads to conditions of better health, sound sleep and there by mental peace.
4. It promotes happiness in day to day life.

Question 6.
What is growth? How does it take place?
Answer:

1. Growth is one of the characters in human beings.
2. They grow in size over a period of time till the size and shape of the adult is achieved.
3. Growth occurs by addition of new materials to the cells in the body.
4. Thus we grow to certain height for certain time only.
5. These changes takes place in adolescence at maximum pace.

Question 7.
Why are children in adolescence in confusion state?
Answer:
Children in adolescence are in confusion because they grow from childhood to adolescence. They have lot of stress due to changes in the body and are unable to decide whether they belong to adulthood or childhood.

Question 8.
In what way the kind of discrimination is harmful for girls and women during the period of menstural cycle?
Answer:

1. Some sections of people in our society believe that during the period of menstruation women are untouchable.
2. During this time girls may be restricted from taking bath, cooking food or going to school.
3. By separation of the girls in that particular period, it would be known to all, and the girl may feel shy, unable to move freely with others.
4. She becomes dull in studies.

Question 9.
What should be done at the time of pimples and acne?
Answer:

1. Do not scratch the pimples.
2. Wash your face regularly with a mild soap.
3. Use luke warm water to wash pimples and acne.
4. Never get worried of pimples and acne because stress and strain may help them to increase.

Question 10.
Write how child marriages cause damage to her health. (OR)
Child marriage is a social evil. What problems would occur due to early marriage?
Answer:

1. Teenage mothers are not prepared mentally for motherhood.
2. Early marriage and motherhood cause health problems in the mother and child.
3. It also curtails employment opportunities for the young woman and may cause mental agony as she is not ready for responsibilities of motherhood.

8th Class Biology 5th Lesson Attaining the Age of Adolescence 4 Marks Important Questions and Answers

Question 1.
How do you understand that you have reached the age of adolescence?
Answer:

1. Moustaches growing on upper lip.
2. Change in voice.
3. External hair grows under armpits.
4. Taking care of face by applying powder and combining hair frequently.
5. Feeling shy when talking with opposite sex.
6. Interested to play with opposite sex.
7. Showing restlessness while parents suggest to do something.

Question 2.
Is it apt to believe in the myth of keeping away women untouchable during the period of menstrual cycle?
Answer:

1. In olden days it was believed that the women during their menstrual period were kept aside and were also forced to stay in huts built in out skirts of the village.
2. In those days the women are the home makers and are not job holders.
3. They have leisure to follow all the restrictions.
4. And also there is scientific reason that during menstrual cycle, a woman need rest completely.
5. They believed that it can be strictly followed by exposing it is a myth.
6. So it was followed as restriction.

Question 3.
To make future in a right way an adolescent need to know more about adolescence. Do you agree?
Answer:

1. Attraction towards opposite sex is a normal response.
2. Full of zealous acts and urge to find reasons of several things around.
3. Emotional state at all the time and get new thoughts for the life activities.
4. Behave in a different as compared to what they did during childhood with peers and elders.
5. More independent in nature and very self conscious.
6. Feel insecure while trying to adjust to the changes in the body and the mind.
7. They need a lot of attention, love and care as well as answer to all their queries regarding their body and self development.

Question 4.
Consuming Gutkha, Cigarettes, Cigar, Beedi, Khaini has become a social evil – Is it true ?
Answer:
Yes. It is true.

1. A number of addicted people at the age of 15 or below is 57.57 lakhs (68%) in Andhra Pradesh.
2. When they reach 30 years of age their internal organ system becomes damaged, and this leads to severe problems.
3. Sometimes, may cause death also.
4. It is dangerous alarm in our country.
5. So adolescents should be aware of healthy habits.

Question 5.
Draw and write short notes on Adam’s apple.
Answer:
Adam’s apple:

1. The Adam’s apple is actually a partial growth of our voice box or larynx.
2. The larynx is made up of nine cartilages, one of which is the largest, called thyroid cartilage.
   
3. Due to the elongation of the thyroid cartilage the Adam’s apple is formed. It protrudes out in front of the
4. This is caused mainly by male hormone testosterone during adolescence.
5. As a result muscles or chords attached to the cartilage get loosened and thickened.
6. When air passes through these chords a hoarse sound is produced.
7. This is the reason for distrubance in voice in the stage of adolescence. At the end of this stage voice get perfect.

Question 6.
Draw and label the diagram of position of some endocrine glands in the human body.
Answer:

Question 7.
Adoloscence is the energetic state. What health and good habits you want to develop?
(OR)
What hygienic steps you would follow as an adolescent to keep yourself clean and healthy?
Answer:
Adolescence is the energetic stage. It is the age when growth and development takes place at faster rate. They need good nutrition support. That is why they have to plant to take balanced diet with fruits, milk, egg and iron rich foods. They must say no to junk foods. Cleanliness is more important in this stage to avoid several bacterial, fungal infections. So it would better to take bath twice in a day. Air body parts and inner wears should be washed with fat rich soaps. No to creams, liquids etc. Girls should take special care of cleanliness during the time of menstrual cycle. Making use of disposable napkins may reduce chance of infections. All young ones should take a walk, exercise and play outdoor games. The physical activity leads to conditions of better health. Better to sleep early and awake early in the morning is a good sleeping habit. Think positive is good keep confidence and free from stress. Better to consult your parent, teacher or a doctor to clear the doubts and mental stress. And say no to drugs, alcohol and other stress relievers. Peers don’t have much knowledge in these problems, so better to take advices from parents and teachers. Practicing of different life skills makes an adolescent free from all hazards and become a good citizen.

8th Class Biology 5th Lesson Attaining the Age of Adolescence Important Questions and Answers

Question 1.
1) What is the name of the following picture?
2) In which stage this is developed?
3) In whom, this organ will develop more? What will happen?
4) Which cartilage elongation this will form?
Answer:
1) Adam’s apple.
2) Adam’s apple develops during adolescence in boys.
3) Because of this, the voice in boys become coarse.
4) It is formed due to the growth of thyroid cartilage.

Question 2.
Observe the following table and answer the following questions.

1) Which hormone released at the time of anger?
2) Which gland release the testosterone hormone?
3) Which hormone controls the other endocrine glands?
4) Which hormones causes the secondary sexual characters in males and females?
Answer:
1) Adrenalin
2) Testes
3) Growth hormone
4) Testosterone, Estrogen

Question 3.
To know more details about given picture what questions do you ask your biology teacher?

Answer:

1. Name the structure shown in the above figure.
2. How does this structure grow?
3. In whom can you observe this structure?
4. What changes do you observe in boys after the development of Adam’s apple?

Question 4.
Correct the statements and if necessary rewrite.
a) To observe nucleus and cell organelles clearly staining is not necessary.
b) Cell wall controls cell functions.
Answer:
a) To observe nucleus and other cell organelles, staining is very essential.
b) Cell wall provides mechanical strength to the cell. It protects the plant cell from external shocks.

Question 5.
Based on the information given in the table, answer the following questions.

a) Where did the sperms produced? Which hormone is responsible for it?
b) Which hormone controls emotions?
c) What are the functions of the hormones produced by ovaries?
d) Why should we call some glands as endocrine glands?
Answer:
a) Sperm is produced by Testes. Testosterone is responsible for the production of sperm.
b) Adrenalin
c) Release of ovum, menstruation, and secondary sexual characters in female.
d) Endocrine glands do not have ducts to release their secretions. They directly release hormones into blood. Hence they are called ‘endocrine glands’.

Question 6.
Mallika was 15 years old. Her parents decided to get her married. Is this correct?
Answer:

1. The decision taken by the parents of Mallika is wrong.
2. In our country the legal age for marriage is 18 years for girls and 21 years for boys.
3. Teenage mothers are not prepared mentally or physically for motherhood.
4. Early marriage and motherhood cause health problems for the mother and the child.
5. It also curtails employment opportunities for the young woman and may cause mental agony as she is not ready for responsibilities of motherhood.

Question 7.
Read the following passage and answer the questions.
In females, the reproductive phase of life begins usually around 10-12 years of age and generally lasts till the age of approximately 45-50 years. On the onset of adolescence, the ova begins to mature. One ovum matures and is released by one of the ovaries once in about 28 to 30 days. During this period the wall of the uterus becomes thick so as to receive a fertilized egg and this results in pregnancy. If fertilization does not occur, the released egg and thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is called ‘Menstruation ’.
i) In humans, what is the age at which menstrual cycle is generally observed ?
ii) What happens during menstruation
Answer:
i) 10 or 12 years to 45 – 50 years.
ii) During this period, the wall of the uterus becomes thick so as to receive a fertilized egg and this results in pregnancy. If fertilization does not occur, the released egg and thickened lining of the uterus along with it’s blood vessels are shed off. This causes bleeding in women which is called “Menstruation”.

Question 8.
Match the following.
Group -1                                                         Group – II
A) Adrenalin                                            1) General growth
B) FSH                                                     2) Secondary sexual characters
C) Estrogen                                             3) Sends egg into fallopian tube
D) Growth Hormone                               4) Directs testosterone to produce sperms
5) Controls emotion
Answer:
A – 5
B – 4
C – 2
D – 1

AP State Syllabus AP Board 8th Class Physical Science Important Questions Chapter 2 Friction

AP State Syllabus 8th Class Physical Science Important Questions 2nd Lesson Friction

8th Class Physical Science 2nd Lesson Friction 1 Mark Important Questions and Answers

Question 1.
What is frictional force?
Answer:
The force which opposes the relative motion of two surfaces of bodies which are in contact is called frictional force.

Question 2.
What is static friction?
Answer:
Static friction is the friction which comes into play when surfaces of objects are at rest relative to each other

Question 3.
What is sliding friction?
Answer:
Sliding friction is the friction which comes into play when the surface of one object moves relative to the surface of another object.

Question 4.
What is rolling friction?
Answer:
When one body rolls over the surface of the other body the friction offered is called rolling friction.

Question 5.
Write the order of friction.
Answer:
Static friction > Sliding friction > Rolling friction.

Question 6.
What are lubricants?
Answer:
The substances which reduce friction are called lubricants.

Question 7.
What are the factors which influence friction?
Answer:
The factors which influence friction are: 1) Nature of surface, 2) Normal force.

Question 8.
What is drag?
Answer:
The frictional force exerted by fluids is called drag.

Question 9.
What are the factors which frictional force of an object in fluid depends on?
Answer:
The frictional force of an object in a fluid depepds on its speed with respect to fluid and on the shape of the object and nature of the fluid.

Question 10.
If friction was absent can you light a match stick?
Answer:
No, to light a match stick it is to be rubbed against the rough surface of a match box.

Question 11.
Hard metal balls are used between rolling parts in a machine. How does it reduces friction?
Answer:
Firstly it reduces the area of contact and reduces the friction. Secondly the hard balls experiences small forces of deformation that also reduce friction.

Question 12.
When a car is speeding on a level track, it enters on a concrete road from a tar road. What happens to its speed when the acceleration is unchanged?
Answer:
The friction between the tyres and the concrete road is less than that on the tar road. Therefore, the car accelerates more on the concrete road.

Question 13.
A car moving on a concrete road entered on a glacier. The driver applied brakes. Describe its motion.
Answer:
Because the friction is almost zero on the glacier, the car would not stop even though the tyres stop moving. That is the car skid forward.

Question 14.
Why do we use grease between moving parts of motor vehicles?
Answer:
To reduce friction and increase the efficiency of motor vehicles.

Question 15.
What is effect of roughness on friction?
Answer:
As the roughness of surface increases frictional force increases.

Question 16.
Why do Gymnasts apply some coarse substance on their hands?
Answer:
Gymnasts apply some coarse substance on their hands to increase friction for better grip.

Question 17.
What is the effect of area of contact on frictional force?
Answer:
Frictional force is independent of area of contact.

Question 18.
Why do we need to change the tyres when its threading is worn out?
Answer:
If we does not change the tyre then the frictional force decreases due to threading worn out tyre there by the vehicle may skid.

Question 19.
Why birds and fishes have special shapes?
Answer:
Birds and fishes have to move about in fluids all the time so they have special shapes which would make them not to lose much energy in overcoming friction.

Question 20.
Why shape of aeroplane is similar to bird?
Answer:
The shape of birds are useful in reducing the fluid friction so aeroplane shape was made similar to bird in order to reduce fluid friction.

Question 21.
How does life history of Leonardo Davinci inspire students?
Answer:
Leonardo Davinci was concerned with laws of science and nature which greatly informed his work as a painter, sculptor, inventor and draft men. His versatile personality inspire students.

8th Class Physical Science 2nd Lesson Friction 2 Marks Important Questions and Answers

Question 1.
What is practical application of static friction?
Answer:

1. The objects unable to move on their own is due to static friction otherwise no object be stationary at a particular place.
2. All the objects we used in our daily life are stationary because they unable to over-come static friction.

Question 2.
Why frictional force increases with roughness?
Answer:

1. Friction caused by the irregularities on the two surfaces which are in contact.
2. Irregularities on the two surfaces lock into one another and we have to apply force to overcome interlocking to move any surface.
3. On roughness surfaces there exists a large number of irregularities so the force of friction is greater if a rough surface is involved.

Question 3.
Give few examples for Sliding friction.
Answer:

1. The trolley moves on the floor.
2. The marbles or any spherical objects slide on the ground or floor when thrown.
3. The tyres make sliding movement on roads which moves the vehicles.

Question 4.
What happens if we do not reduce friction in machines?
Answer:
If we do not reduce friction in machines, then friction causes overheating and wearing out of moving parts of machinery.

Question 5.
What purposes are surved by using bearings in machines? Explain with daily life examples.
Answer:
Ball bearings are used to reduce friction between rotating shafts of machine tools.

1. Ball bearings are used in fAnswer:
2. Ball bearings are also used in machines.

Question 6.
Give examples of practical application of static friction.
Answer:

1. The static friction does not make the bodies move easily. So, the bodies are at rest.
2. The static friction helps the vehicles to come to rest.
3. The static friction helps us to escape from slippery.

Question 7.
Why does friction between two surfaces increase when they are pressed harder?
Answer:
Since the friction is due to the interlocking of irregularities in the two surfaces which slide with respect to each other, it is obvious that the force of friction will increase if the two surfaces are pressed harder.

Question 8.
Describe some examples where heat is produced due to friction.
Answer:

1. When we rub our hands together vigorously for few minutes we feel heat due to friction.
2. When we strike a matchstick, against rough surface, it catches fire due to friction.

Question 9.
Why are the soles of our shoes and tyres of cars, trucks, etc. grooved?
Answer:

1. It is done to provide the shoes better grip on the floor, so that one can move safely.
2. Similarly, the threaded tyres of cars, trucks and buldozers provide better grip with the ground.

Question 10.
Why heavier box apply more frictional force than lighter box?
Answer:

1. We know that the force of friction is increased if the two surfaces are pressed harder.
2. A heavier box presses the ground harder to heavier box apply more frictional force.

Question 11.
Why it is easy to move an object in motion when compared with object at rest?
Answer:

1. When the box start moving, the contact points on its surface, do not get enough time to lock into the contact points of floor.
2. So it is easy to move the box which already started to move.

Question 12.
What is the function of ridges on your palm and bottom of your feet?
Answer:
Ridges of our palm help us to make firm grip whenever we hold by our hands – Ridges of the bottom of our feet help us to walk freely and we do not slip because of these.

Question 13.
On what factors does the fluid friction depend?
Answer:

1. The frictional force on an object in a fluid depends on its speed with respect to the fluid.
2. The frictional force also depends on the shape of the object and the nature of the fluid.

Question 14.
Describe some examples where we have to increase friction.
Answer:

1. We will increase friction by using brake pads in the brake system of bicycles and automobiles.
2. Kabaddi players rub their hands with the soil for an easy grip of their opponents.
3. Gymnasts apply some coarse substances on their hands to increase friction for better grip.

Question 15.
Why is it easy to drag a mat over the floor when no weight is kept over it?
Answer:

1. When weight is kept over the mat, more force will be applied.
2. Due to more force, interlocking of two surfaces will increase, so friction also increases.
3. That is why it is easy to drag a mat over the floor when no weight is kept over it.

Question 16.
Explain why we use ball bearings between the hub and axle of ceiling fan and bicycle?
Answer:

1. Since the rolling friction is smaller than the sliding friction.
2. So sliding is replaced in most machines by rolling with the use of ball bearings.
3. Common examples are the use of ball bearings between the hub and axle of a ceiling fan and the bicycle.

Question 17.
Explain why Gymnasts apply some coarse substance on their hands?
Answer:

1. Gymnasts apply some coarse substance on their hands to increase friction for better grip.
2. This is due to increasing the large number of irregularities (up & downs) in the contact area.

8th Class Physical Science 2nd Lesson Friction 4 Marks Important Questions and Answers

Question 1.
What are the forces acting on a moving body on a floor?
Along vertical direction: Weight of the body (W) or gravitational force acting vertically down.

Normal force (N) or reaction force applied by the floor vertically up.
As there is no change in the motion of the body f along vertical direction the net force along vertical direction is 0.
That is W – N = 0 ⇒ W = N
Along horizontal direction : In horizontal direction the speed of the body changing gradually due to force, applied by the floor on the body. The force applied by the floor on the body is called frictional force.

Question 2.
What kinds of friction do you know and explain with suitable example.
Friction is of four kinds. They are:

1. Static friction: Friction which comes into play when surfaces of the objects are at rest relative to each other.
   Ex: 1) We are applying force on a big rock but unable to move the rock due to its static friction.
   2) Block at rest relative to the surface of trolley upto a certain limiting acceleration.
2. Sliding friction : The friction which comes into play when the surface of one object moves relative to the surface of another object.
   Ex: When the applied force is more than limit of static friction, then the object starts to move which is example for sliding friction.
3. Rolling friction : When one body rolls over the surface of another body, the friction offered is called rolling friction.
   Ex: It is easy to pull a suitcase which has rollers.
4. Fluid friction : Friction exerted by fluids like liquids and gases is called fluid friction. Ex : The shape of birds are such that they overcome the fluid friction.

Question 3.
A book placed on the surface of a table. The book is pushed in one direction. Draw the forces acting on the book and explain.
Answer:
The weight acts downwards and normal force acts upward direction they balance each other.

Whereas frictional force acting opposite to the applied force.

Question 4.
Explain with one example that Frictional force is proportional to the Normal force.
Answer:
Keep a brick on the horizontal floor tied to the spring balance. Pull the spring balance and note the frictional force.
Do the same experiment by adding one more brick above the first one.
Tie a brick to the spring balance and pull it to find the frictional force. The normal force acts on it provides a frictional force.

When we pull a brick over another brick the normal force acting on them increases so that the frictional force increases.
∴ Friction °c Normal force

Question 5.
Scientists designed the shape of aeroplane using the technique of reducing fluid friction by observing birds shape. How would you appreciate?
Answer:

1. Objects move through fluids, they have to overcome friction acting on them.
2. Birds and fishes have to move about in fluids all the time.
3. Their bodies must have evolved to shapes which would make them not to lose much energy in overcoming friction.
4. So aeroplanes designed in a special shape to overcome friction without loosing much energy.
   Hence I appreciate the idea of scientists to overcome fluid friction by designing shape of aeroplane.

Question 6.
Conduct an experiment to findout the effect of roughness on frictional force.
Answer:
Effect of roughness on frictional force:

1. Set up an inclined plane on the horizontal floor. Use a wooden board as inclined plane.
2. Put a mark at any point A on the inclined plane. Now let a pencil cell or ball move down from this point.
3. Note the distance covered by the pencil cell from the bottom of the inclined plane to point where it comes to stop.
4. Now, spread a cloth over the floor make sure that there are no wrinkles in the cloth.
5. Try again with pencil cell. Now note down the distance.
6. Distance covered by pencil cell is less in this case.
7. Thus we conclude that smoothness/ roughness of the surfaces of both the floor and the pencil cell could affect the distance travelled by it.

Question 7.
Collect information about the substances using to reduce the friction in different machines and prepare a report on it.
Answer:

1. Adding lubricants to machinery parts.
2. Using roller type ball bearings.
3. Using air pressure to separate moving parts.
4. Using magnetic repulsion to separate moving parts.
5. Using materials that tend to slide easily over each other.
6. Regulate the temperature of the machine.
7. The use of drive shafts.

Question 8.
Write an experiment to identify forces acting on a body and effect of frictional force.
Answer:
Gently push a book or any object on a horizontal floor. It moves for a certain distance and stops due to the friction.
The friction acts in the opposite direction of the force exerted.
Now take the same object and do the activity on different surfaces smooth and rough.
The object moves a long distance on the smooth surface whereas it moves a little distance on the rough surface.
We come across that the friction is more on the rough surface and less on the smooth surface due to the reduction in the sliding friction.

Question 9.
Friction – an evil master and good servant to man. Describe.
Answer:
Friction is the obstruction force acting in the opposite direction of the exerted force. It brings the following bad or evil impacts on the bodies.

1. Over heating and wearing out of moving parts in all machinery
2. Loss of efforts

In this way it is a bad or evil master to man.
But, without friction the moving of vehicles on the roads, walking, running, sitting, standing, etc. of us are not possible.
We are able to write with pen or pencil on the papers or walls or any surface is only due to the influence of friction. .
In this way it is a good master.

Question 10.
Does the friction is affected by smoothness of surface? Explain.
Answer:

1. Friction is caused by the irregularities on the two surfaces in contact.
2. Even those surface which appear very smooth have a large number of minute irregularities on them.
3.  Irregularities on the two surfaces lock into another.
4. When we attempt to move any one surface over the other, we have to apply a force to overcome interlocking.
5. On rough surfaces, there are a larger number of irregularities.
6. So the force of friction is greater if a rough surface is involved.

Question 11.
What would happen if there were no force of friction? Imagine and describe in your own words.
Answer:

1. If there were no friction, many problems could have been arisen, as one will not able to walk if they were no friction at all.
2. One could not write with pen or pencil.
3. One could not write on blackboard with a chalk.
4. If any object just started moving, it would never stop.
5. Had there been no friction between the tyres of the automobiles and the road, they could not be started or stopped or turned to change the direction of motion.
6. One could not fix the nail in the wall or tie a knot.
7. Without friction no buildings could be constructed.

8th Class Physical Science 2nd Lesson Friction Important Questions and Answers

Question 1.
“Friction produce heat” – suggest an activity to prove this.
Answer:

1. Rub your palms against each other for a few minutes.
2. You can feel heat in your palms.
3. Hence we can say that friction produces heat.

Question 2.
Write any one precaution which was taken by you while doing the experiment to understand the nature of friction.
Answer:
Keep the weights to the hanger slowly and one by one.

Question 3.
Give any two examples of ways of reducing friction.
Answer:
We can reduce friction,

1. by using lubricants in between frictional surfaces,
2. by using ball bearings in the rotating parts.

Question 4.
If there is no frictional force, assume the consequences in your classroom. Write any four of them.
Answer:
If there is no friction force,

1. We cannot hold a pen to write on a book.
2. We cannot walk in the classroom.
3. Teacher cannot write with chalk-piece on the blackboard.
4. Heat does not produce when rub the palms against each other.

Question 2.
What is fluid friction? Explain why objects moving in fluids must have special shapes.
Answer:

1. When bodies move through fluids, fluids exert a frictional force called drag or fluid friction.
2. To minimise fluid friction, objects moving in fluids must have special shapes.
3. For example, Birds and Fishes have to move about in fluids all the time, so they have special shapes which would make them not to lose much energy in over coming friction.
4. Another example is the shape of aeroplane was made similar to bird in order to reduce fluid friction.

Question 3.
Imagine the friction has disappeared from the earth. What will happen? Explain.
Answer:

1. If there were no friction, many problems could have been arisen, as one will not able to walk if they were no friction at all.
2. One could not write with pen or pencil.
3. One could not write on blackboard with a chalk.
4. If any object just started moving, it would never stop.
5. Had there been no friction between the tyres of the automobiles and the road, they could not be started or stopped or turned to change the direction of motion.
6. One could not fix the nail in the wall or tie a knot.
7. Without friction no buildings could be constructed.

Question 4.
Name any two types of frictions. Write one example for each.
(OR)
What kinds of friction do you know? Write the conditions needed for static friction between two objects and what way do you suggest to reduce friction?
Answer:
Friction is of four kinds. They are

1. Static friction: Friction which comes into play when surfaces of the objects are at rest relative to each other.
   Ex : 1) We are applying force on a big rock but unable to move the rock due to its static friction.
   2) Block at rest relative to the surface of trolley upto a certain limiting acceleration.
2. Sliding friction: The friction which comes into play when the surface of one object moves relative to the surface of another object.
   Ex : When the applied force is more than limit of static friction, then the object starts to move which is example for sliding friction.
3. Rolling friction: When one body rolls over the surface of another body, the friction offered is called rolling friction.
   Ex : It is easy to pull a suitcase which has rollers.
4. Fluid friction: Friction exerted by fluids like liquids and gases is called fluid friction. Ex : The shape of birds are such that they over come the fluid friction.

Static friction is a self adjusting force. The following conditions are needed for static friction ;

1. Roughness of the surface of contact and
2. Normal force.
3. We can reduce the friction by applying oil or grease between the moving parts of a machine.
4. If we polish the rough surfaces, they become smooth and friction is reduced.
5. We can apply soap solution to the rough surfaces.
6. We can apply powder of small quantity on the surface.
7. By streamlining the bodies of the vehicles we can reduce air friction.

Question 5.
Friction does not depends upon area of contact. How can you perform an activity to prove it?
Answer:
Tie a string around a brick and pull the brick by using spring balance and measure the applied force or friction.

Now turn the brick upright so that the contact area with the floor becomes small. Do the same experiment and measure the friction using the reading of the spring balance.

The conclusion is frictional force appears the same in both the cases irrespective of area of contact.