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NCERT Solutions for Class 8 Science Chapter 13 Sound are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 13 Sound.

NCERT Solutions for Class 8 Science Chapter 13 Sound

NCERT TEXTBOOK EXERCISES

Question 1.
Choose the correct answer:
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases
Answer.
(d) solids, liquids and gases.

Question 2.
Voice of which of the following is likely to have minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Answer.
(b) Baby boy.

Question 3.
In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false:

1. Sound cannot travel in a vacuum. (T/F)
2. The number of oscillations per second of a vibrating object is called its time period. (T/F)
3. If the amplitude of vibration is large, the sound is feeble. (T/F)
4. For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
5. The lower the frequency of vibration, the higher is the pitch. (T/F)
6. Unwanted or unpleasant sound is termed music. (T/F)
7. Noise pollution may cause partial hearing impairment. (T/F)

Answer.

1. True
2. False
3. False
4. True
5. False
6. False
7. True

Question 4.
Fill in the blanks with suitable words:

1. Time taken by an object to complete one oscillation is called…….
2. Loudness is determined by the………..of vibration.
3. The unit of frequency is………….
4. Unwanted sound is called……….
5. The shrillness of a sound is determined by the.……….of vibration.

Answer.

1. time period
2. amplitude
3. Hertz (Hz)
4. noise
5. frequency.

Question 5.
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer.

Question 6.
The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Answer.
Number of vibrations per second = 500
Time period = time is taken for one vibration

Question 7.
Identify the part which vibrates to produce sound in the following instruments:

1. Dholak
2. Sitar
3. Flute

Answer.

1. Stretched membrane
2. String of sitar
3. Air column.

Question 8.
What is the difference between noise and music? Can music become noise sometimes?
Answer.
The unpleasant sound is called noise, whereas a pleasant sound is called music. Noise can produce so many health hazards, whereas music brings about a soothing effect. Yes, music can become noise sometimes when the musical instruments produce very high volume sounds.

Question 9.
List sources of noise pollution in your surroundings.
Answer.
Following are the major sources of noise pollution:

1. Sounds of vehicles.
2. Sounds of the bursting of crackers and explosives.
3. Sounds of loudspeakers, TVs, transistors.
4. Sounds of kitchen appliances.
5. Sounds of desert coolers, air conditioners etc.

Question 10.
Explain in what way noise pollution is harmful to humans.
Answer.
Noise pollution may cause many health-related problems.

• Lack of sleep, hypertension (high blood pressure), anxiety, etc. are some of the problems that may be caused due to noise pollution.
• A person who is exposed to a loud sound continuously may get temporary or even permanent deafness.

Question 11.
Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer.
I would suggest my parents buy the house which is three lanes away from the roadside. This would protect us from noise pollution which is maximum on the roadside.

Question 12.
Sketch the larynx and explain its function in your own words.
Answer.
In humans, the sound is produced by the voice box or the larynx. It is situated in the throat. Below it is the windpipe. The two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air when the lungs force air through the slit, the vocal cords vibrate and the vibration results in sound.

Question 13.
Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
Answer.
The light travels at the speed of 3 x 10s ms-1, which is very large in comparison to the speed of sound which travels at the rate of 330 ms-1 in the air. That is why lightning is seen earlier and thunder is heard later.

We hope the NCERT Solutions for Class 8 Science Chapter 13 Sound helps you. If you have any query regarding NCERT Solutions for Class 8 Science 13 Sound, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 12 Friction are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 12 Friction.

NCERT Solutions for Class 8 Science Chapter 12 Friction

NCERT TEXTBOOK EXERCISES

Question 1.
Fill in the blanks:

1. Friction opposes the…………….between the surfaces in contact with each other.
2. Friction depends on the.…………..of surfaces.
3. Friction produces ……………….
4. A sprinkling of powder on the carrom board.…………….friction.
5. Sliding friction is……….than the static friction.

Answer.

1. relative motion
2. smoothness (or irregularities or nature)
3. heat
4. reduces
5. less.

Question 2.
Four children were asked to arrange forces due to rolling, static, and sliding frictions in decreasing order. Their arrangements are given below. Choose the correct arrangement.
(a) rolling, static, sliding
(b) rolling, sliding, static
(c) static, sliding, rolling
(d) sliding, static, rolling
Answer.
(c) static, sliding, rolling.

Question 3.
Alida runs her toy car on the dry marble floor, wet marble floor, newspaper, and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be
(a) wet marble floor, dry marble floor, newspaper, and towel,
(b) newspaper, towel, dry marble floor, wet marble floor,
(c) towel, newspaper, dry marble floor, wet marble floor,
(d) wet marble floor, dry marble floor, towel, newspaper.
Answer.
(a) wet marble floor, dry marble floor, newspaper, and towel.

Question 4.
Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Answer.
The frictional force will act parallel to the inclined surface, opposite to the direction of the sliding of the book.

Question 5.
You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Answer.
It is difficult to walk on a soapy floor because a soapy floor applies very little friction and hence we can slip on such floors.

Question 6.
Explain why sportsmen use shoes with spikes.
Answer.
Sportsmen use shoes with spikes because spikes produce the desired frictional force and thus help in holding the ground firmly.

Question 7.
Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Answer.
We know that the force of friction is increased if the two surfaces are pressed harder. A heavier box will apply more pressure on the floor and hence Seema will experience more frictional force.

Question 8.
Explain why sliding friction is less than static friction.
Answer.
Friction is caused by the interlocking of irregularities in the two surfaces. When the object starts sliding, the contact points on its surface, do not get enough time to lock into the contact points of the other surface. So, the sliding friction is slightly smaller than the static friction.

Question 9.
Give examples to show that friction is both a friend and a foe.
Answer.

Friction is both friend and foe, that is why it is said that friction is a necessary evil.

1. Friction as a friend:

• To hold a glass, we have ridges on our palm, which increase the friction between palm and glass.
• We are able to write anything with a pen or pencil because there is friction between the surfaces of paper and the point of a pen (nib) or pencil.
• A teacher can write on the blackboard with chalk because of the friction between the black-board surface and the chalk.
• If there is no friction, then a moving body would never stop.
• A nail could not be fixed in the wall, or a knot could not Be tied, had there been any friction.
• No building could be constructed without friction.

2. Friction as a foe:

• Friction wears out materials, whether they are screws, ball-bearings, or soles of shoes.
• Friction can also produce heat, which increases the wear and tear of machine parts. It also causes much wastage of energy, because this heat is not utilized.

Question 10.
Explain why objects moving in fluids must have special shapes.
Answer.
Birds and the fishes have to move about in fluids all the time. Thus, their “bodies have evolved to shapes which make them not to lose much energy in overcoming fluid friction. Such shapes are called streamlined. Cars are also designed so that their shapes resemble the streamlined shapes of birds, fishes, etc.

We hope the NCERT Solutions for Class 8 Science Chapter 12 Friction help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 12 Friction, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure.

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure

NCERT TEXTBOOK EXERCISES

Question 1.
Give two examples of each of situations in which you push or pull to change the state of motion of objects.
Answer.
(1) If a rubber ball or marble is placed on a very smooth surface and given a small push, it starts moving with some speed. If we keep an obstacle in the way of motion of the marble/ball, the marble/ball will stop moving at the obstacle. Here a push is given to the marble/ball at rest to change its state of rest to motion.

(2) If a child is placed on a hanging swing in the state of rest and the swing is pulled again and again by a rope, the swing will move to and fro with a speed. If the pull is bigger, the swing will move at a bigger distance. This is an example of a pull that changed the state of an object from the rest of the motion.

Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer.

1. If an inflated balloon is taken and pressed from two sides with a hand, its shape changed, i.e., the figure is disturbed. If the inflated balloon is pressed with more force, the balloon will burst.
2. If a plate of steel is beaten with a hammer, after four-five big blows the plate’s shape will change.

Question 3.
Fill in the blanks in the following statements:

1. To draw water from a well, we have to ……….. at the rope.
2. A charged body………….an uncharged body towards it.
3. To move a loaded trolley, we have to…………...it.
4. The north pole of a magnet…………….the north pole of another magnet.

Answer.

1. pull
2. attracts
3. pull/push
4. repels.

Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms: muscular, contact, non-contact, gravity, friction, shape, attraction.

1. To stretch the bow, the archer applies a force that causes a change in its……..
   
2. The force applied by the archer to stretch the bow is an example of.………..force.
3. The type of force responsible for a change in the state of motion of the arrow is an example of a…………….force.
4. While the arrow moves towards its target, the forces acting on it are due to……….and that due to of air.

Answer.

1. shape
2. muscular
3. contact
4. gravity, friction.

Question 5.
In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer.

Question 6.
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.
The shape of the hot piece of iron changes. It flattens and becomes thinner than earlier. This is the effect of force due to hammering the piece of iron.

Question 7.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer.
Electrostatic force.

Question 8.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer.
The forces that act on the bucket are as follows:

1. The pressure of water contained in it exerted on its wall and on the base of the bucket.
2. Force of gravity exerted by earth.
3. Muscular force by my hand.

The water is contained in a bucket and the pressure is exerted by water on the walls of the bucket, which is sufficient to take it as a force. This force is counterbalanced by the force exerted by the walls of the bucket on water. As the bucket (with water) is held in my hand, so I overcome the force of gravity of the earth.

Thus, it can be concluded that there is no net effect of forces acting on the bucket full of water. That is why these forces do not bring a change in its state of motion.

Question 9.
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.
The two forces that are acting on the rocket immediately after leaving the launching pad are:

1. Force of gravity of earth acting down-ward
2. The frictional force produced by air particles.

Question 10.
When we press the bulb of a dropper with its nozzle kept in water, the air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
(a) pressure of water
(b) the gravity of the earth
(c) the shape of a rubber bulb
(d) atmospheric pressure
Answer.
(a) the pressure of water.

We hope the NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence.

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence

NCERT TEXTBOOK EXERCISES

Question 1.
What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?
Answer.
The term used for secretions of endocrine glands is hormones, which are responsible for various changes taking place in the body.

Question 2.
Define adolescence.
Answer.
The period of life when the body undergoes changes, leading to reproductive maturity is called adolescence.

Question 3.
What is menstruation? Explain.
Answer.
When the uterus receives the egg and it is fertilized, pregnancy occurs. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off: This causes bleeding in women, which is called menstruation.

Question 4.
List changes in the body that take place at puberty.
Answer.
The onset of puberty brings about:

1. Growth of the reproductive organs which begin to function.
2. Hair grows at various places of the body. Breasts develop in girls and facial hair (mustache and beard) appear in boys.
3. The voice of the boys becomes hoarse as the voice box enlarges during adolescence.

Question 5.
Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer.

Question 6.
What are sex hormones? Why are they named so? State their function.
Answer.
Hormones secreted by testes and ovaries are termed as sex-hormones.

• They are named so because they are secreted by the reproductive organs.

Functions of sex-hormones.

• These hormones are responsible for the secondary sexual characters of males and females.

Question 7.
Choose the correct option.
(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
Answer.
(ii) proper diet is needed for the rapid growth taking place in their body. Reproductive age in women starts when their

(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
Answer.
(i) menstruation starts.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
Answer.
(ii) Chapati, dal, vegetables.

Question 8.
Write notes on:

1. Adam’s apple.
2. Secondary sexual characters.
3. Sex determination in the unborn baby.

Answer.

1. At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. This makes a boy’s voice hoarse.
2. In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, mustaches and beards. As these features help to distinguish the male from the female, they are called secondary sexual characters.
3. Sex Determination in the Unborn Baby: All human beings have 1 pair of sex chromosomes, as the names X and Y. A female has two X chromosomes,

while male has one X and one Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote, that will have ‘XT would develop into a male child. Now you know that the sex chromosomes of the father determine the sex of a baby.

Question 9.
Word game: Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through the bloodstream
6. Voicebox
7. Term for changes at adolescence.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals.

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Explain the importance of reproduction in organisms.
Answer.
The production of new individuals from their parents is known as reproduction. Reproduction is very important as it ensures the continuation of a species. If the process of reproduction does not exist, the species would get vanished from the earth.

Question 2.
Describe the process of fertilisation in human beings.
Answer.
The first step in the process of reproduction is the fusion of a sperm and an ovum. Millions of sperms from the male are transferred into the female body. The sperms swim in the oviduct with the help of their tails to reach the egg. When they come in contact with the egg, one of the sperms may fuse with the egg.

Such fusion of the egg and the sperm is called fertilization. During fertilization, the nucleus of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote.

Question 3.
Choose the most appropriate answer:
(a) Internal fertilisation occurs
(i) in female body.
(ii) outside the female body.
(iii) in male body.
(iv) outside male body.
Answer.
(i) in female body.

(b) A tadpole develops into an adult frog by the process of
(i) fertilisation.
(ii) metamorphosis.
(iii) embedding.
(iv) budding.
Answer.
(ii) metamorphosis.

(c) The number of nuclei present in a zygote is
(i) none
(ii) one
(iii) two
(iv) four.
Answer.
(ii) one.

Question 4.
Indicate whether the following statements are True (T) or False (F):

1. Oviparous animals give birth to young ones. ( )
2. Each sperm is a single cell. ( )
3. External fertilisation takes place in frogs. ( )
4. A new human individual develops from a cell called gamete. ( )
5. Egg laid after fertilisation is made up of a single cell. ( )
6. Amoeba reproduces by budding. ( )
7. Fertilization is necessary even in asexual reproduction. ( )
8. Binary fission is a method of asexual reproduction. ( )
9. A zygote is formed as a result of fertilisation. ( )
10. An embryo is made up of a single cell. ( )

Answer.

1. False
2. True
3. True
4. False
5. True
6. False
7. False
8. True
9. True
10. False

Question 5.
Give two differences between a zygote and a foetus.
Answer.

Question 6.
Define asexual reproduction. Describe two methods of asexual reproduction in animals. ‘
Answer.

The type of reproduction in which only a single parent is involved is called asexual reproduction.

Budding: The asexual reproduction in which an individual develops from buds, which is detached from a parent body is known as budding. For example, Hydra reproduces by this method. Many bulges are found in the parent body of hydra. These bulges called buds to develop into new individuals.

Budding fission: It is a type of asexual reproduction in which an animal reproduces by dividing into two individuals. This type of reproduction is observed in the microscopic organism, amoeba. The reproduction in Amoeba begins by a division of its nucleus into two nuclei. This is followed by a division of its body into two with each part receiving a nucleus. Finally, two amoebae are produced from a single Amoeba.

Question 7.
In which female reproductive organ does the embryo get embedded?
Answer.
The embryo gets embedded in the wall of the uterus (of the female) for further development.

Question 8
What is metamorphosis? Give examples.
Answer.
The drastic change that transforms a larva into an adult is called metamorphosis. Frog, SilkWorm, Honeybee, are some animals in which metamorphosis occurs.

Question 9.
Differentiate between internal fertilisation and external fertilisation.
Answer.

Question 10.
Across
1. The process of the fusion of the gametes.
6. The type of fertilisation in the 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 in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals, drop a comment below and we will get back to you at the earliest.