Class 8

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Question 1.
Complete this flow chart.

Answer:

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

Question 2.
Complete this flow chart.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Answer:

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

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

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

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

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

Improve Your Learning

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

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

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

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

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

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

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

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

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

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

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

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

In cooking:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

8th Class Physical Science Textbook Page No. 105

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

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

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

Activity – 1

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

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

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

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

Activity – 2

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

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

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

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

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

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

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

Activity – 3

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

Answer:

Activity – 4

Question 4.
Identifying uses of coal products:

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

Lab Activity

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

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

Activity – 5

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

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

Misuse of fuel in cooking:

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

Misuse of fuel in industries:

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

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

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

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

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

In cooking:

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

In industry:

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

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

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

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

Improve Your Learning

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

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

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

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

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

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

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

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

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

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

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

Question 9.
Find net forces from the following diagrams:

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

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

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

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

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

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

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

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

Answer:

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

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

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

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

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

Answer:

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

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

Along vertical direction:

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

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

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

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

8th Class Physical Science Textbook Page No. 3

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

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

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

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

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

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

8th Class Physical Science Textbook Page No. 4

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

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

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

8th Class Physical Science Textbook Page No. 6

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

8th Class Physical Science Textbook Page No. 8

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

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

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

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

8th Class Physical Science Textbook Page No. 9

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

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

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

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

8th Class Physical Science Textbook Page No. 13

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

Think and Discuss

8th Class Physical Science Textbook Page No. 5

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

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

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

8th Class Physical Science Textbook Page No. 6

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

8th Class Physical Science Textbook Page No. 8

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

8th Class Physical Science Textbook Page No. 10

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

On A

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

On B

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

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

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

8th Class Physical Science Textbook Page No. 12

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

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

8th Class Physical Science Textbook Page No. 15

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

8th Class Physical Science 1st Lesson Force Activities

Activity – 1

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Activity – 2

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

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

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

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

Activity – 3

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

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

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

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

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

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

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

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

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

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

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

Activity – 4

Question 4.
Visualizing magnetic field:

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

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

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

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

Activity – 5

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

Activity – 6

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

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

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

Activity – 7

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

Activity – 8

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

It is called tension.

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

Lab Activity

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

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

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

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

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

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

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

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

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

Activity – 9

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

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

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

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

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

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

Answer:

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

Activity – 10

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

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

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

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

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

Activity – 11

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

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

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

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

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

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

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

Activity – 12

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

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

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

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

Activity – 13

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

Activity – 14

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

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

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

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

Activity – 15

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Pull:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

2) Frictional force:

3) Normal force:

4) Tension:

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

2) Electrostatic force:

3) Gravitational force:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Answer:

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

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

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

Improve Your Learning

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

1. Earthing
2. Lightning

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

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

Information about earthquake:

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

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

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

Help render by relief organisation:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Activity – 1

Question 1.
Effect of rubbing:

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

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

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

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

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

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

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

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

Lab Activity

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

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

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

Activity – 2

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Activity – 3

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

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

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

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

Activity – 4

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

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

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

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

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

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

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

Activity – 5

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

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

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

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

Measures to be taken in a house when earthquake occurs.

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

Measures to be taken outdoors when earthquake occurs.

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

Activity – 6

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

Devastation due to tsunami:

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

To the environment:

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

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

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

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

Improve Your Learning

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

8th Class Physical Science Textbook Page No. 45

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

8th Class Physical Science Textbook Page No. 46

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

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

8th Class Physical Science Textbook Page No. 53

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

Think and Discuss

8th Class Physical Science Textbook Page No. 46

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

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

8th Class Physical Science Textbook Page No. 47

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

8th Class Physical Science Textbook Page No. 49

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

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

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

8th Class Physical Science Textbook Page No. 50

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

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

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

8th Class Physical Science Textbook Page No. 51

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

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

8th Class Physical Science Textbook Page No. 52

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

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

8th Class Physical Science Textbook Page No. 57

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

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

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

Activity – 1

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

Activity – 2

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

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

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

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

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

Activity – 3

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

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

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

Activity – 4

Question 4.
How strong is nylon?

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

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

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

Activity – 5

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

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

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

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

Activity – 6

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

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

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

Activity – 7

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

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

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

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

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

Activity – 8

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

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

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

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

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

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

Lab Activity

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

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

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

Activity – 9

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

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

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

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

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

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

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

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

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

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

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

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

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

Question 1.
Complete this flow chart.

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

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

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

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

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

Answer:

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

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

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

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

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

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

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

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

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

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

Answer:

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

Answer:

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

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

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

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

Question 9.
Observe this diagram and answer the questions.

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

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

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

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

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

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

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