NCERT Solutions for Class 8 Science Chapter 10 Sound
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Page 1
NCERT
SOLUTIONS
CLASS - 8TH
aglase .co
SOLUTIONS
CLASS - 8TH
aglase .co
Page 2
Book : Science Ncert Solutions | Chapter-13 Science
Class : 8th
Subject : Science
Chapter : 13
Chapter Name : SOUND
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) Sound can travel through solids, liquids, and gases. Sound requires a medium
to travel through. Solid, liquid and gas provide the medium for sound. Hence, sound can
travel through solids, liquids and gases.
Page : 168 , Block name : Exercise
Q2 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. (c) A man
The voice of an adult man is of lower pitch in comparison to the voices of a baby boy, a
baby girl and a woman. Since frequency of a sound is directly proportional to its pitch,
man’s voice is of minimum frequency in comparison to a boy, a girl, or awoman’s voice.
Page : 168 , Block name : Exercise
Q3 In the following statements, tick ‘T’ against those which are true, and ‘F’ against
those which are false.
(a) Sound cannot travel in vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period.
(T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
Page 1 of 6 Aglasem Schools
Class : 8th
Subject : Science
Chapter : 13
Chapter Name : SOUND
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) Sound can travel through solids, liquids, and gases. Sound requires a medium
to travel through. Solid, liquid and gas provide the medium for sound. Hence, sound can
travel through solids, liquids and gases.
Page : 168 , Block name : Exercise
Q2 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. (c) A man
The voice of an adult man is of lower pitch in comparison to the voices of a baby boy, a
baby girl and a woman. Since frequency of a sound is directly proportional to its pitch,
man’s voice is of minimum frequency in comparison to a boy, a girl, or awoman’s voice.
Page : 168 , Block name : Exercise
Q3 In the following statements, tick ‘T’ against those which are true, and ‘F’ against
those which are false.
(a) Sound cannot travel in vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period.
(T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
Page 1 of 6 Aglasem Schools
Page 3
Book : Science Ncert Solutions | Chapter-13 Science
(g) Noise pollution may cause partial hearing impairment. (T/F)
Answer. (a) True
Sound requires a medium to travel through. Since vacuum is devoid of any medium,
sound cannot travel through it.
(b) False
The number of oscillations per second of a vibrating object is known as its frequency.
Time period is the time required to complete one oscillation.
(c) False
Loudness of a sound is proportional to the square of the amplitude of its vibration.
When the amplitude of vibration of a sound is large, the sound is very loud. The sound is
feeble for small amplitude.
(d) True
Humans cannot hear sounds of all frequencies. Humans can hear a sound whose
frequency falls in the range of 20 Hz−20,000 Hz. The sound having frequency out of this
range is inaudible to humans.
(e) False
The pitch of a sound is proportional to its frequency. As the frequency of vibration
increases, the pitch of the sound also increases and vice-versa. A sound is said to be high
pitched if its frequency of vibration is high, and is low pitched for a small frequency of
vibration.
(f) False
Unwanted or unpleasant sounds are known as noise. Sounds that are melodious and
pleasing to ear are known as music.
(g) True
Unwanted or unpleasant sounds are known as noise. If one is subjected to loud
unpleasant sound continuously for a long time, then it may cause temporary hearing
impairment.
Q4 Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called __________.
(b) Loudness is determined by the __________ of vibration.
(c) The unit of frequency is __________
(d) Unwanted sound is called __________ .
(e) Shrillness of a sound is determined by the __________ of vibration.
Answer. (a) Time taken by an object to complete one oscillation is called __time period__.
(b) Loudness is determined by the __amplitude__ of vibration.
(c) The unit of frequency is __hertz (Hz) __.
Page 2 of 6 Aglasem Schools
(g) Noise pollution may cause partial hearing impairment. (T/F)
Answer. (a) True
Sound requires a medium to travel through. Since vacuum is devoid of any medium,
sound cannot travel through it.
(b) False
The number of oscillations per second of a vibrating object is known as its frequency.
Time period is the time required to complete one oscillation.
(c) False
Loudness of a sound is proportional to the square of the amplitude of its vibration.
When the amplitude of vibration of a sound is large, the sound is very loud. The sound is
feeble for small amplitude.
(d) True
Humans cannot hear sounds of all frequencies. Humans can hear a sound whose
frequency falls in the range of 20 Hz−20,000 Hz. The sound having frequency out of this
range is inaudible to humans.
(e) False
The pitch of a sound is proportional to its frequency. As the frequency of vibration
increases, the pitch of the sound also increases and vice-versa. A sound is said to be high
pitched if its frequency of vibration is high, and is low pitched for a small frequency of
vibration.
(f) False
Unwanted or unpleasant sounds are known as noise. Sounds that are melodious and
pleasing to ear are known as music.
(g) True
Unwanted or unpleasant sounds are known as noise. If one is subjected to loud
unpleasant sound continuously for a long time, then it may cause temporary hearing
impairment.
Q4 Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called __________.
(b) Loudness is determined by the __________ of vibration.
(c) The unit of frequency is __________
(d) Unwanted sound is called __________ .
(e) Shrillness of a sound is determined by the __________ of vibration.
Answer. (a) Time taken by an object to complete one oscillation is called __time period__.
(b) Loudness is determined by the __amplitude__ of vibration.
(c) The unit of frequency is __hertz (Hz) __.
Page 2 of 6 Aglasem Schools
Page 4
Book : Science Ncert Solutions | Chapter-13 Science
(d) Unwanted sound is called __noise__.
(e) Shrillness of a sound is determined by the __frequency__ of vibration.
(Shrillness is also called pitch of the sound. Pitch is directly proportional to the
frequency of vibration. Hence, shrillness is determined by the frequency of vibration.)
Q5 A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer. Frequency of oscillations is de�ned as the number of oscillations of a vibrating
body per second. It is given by
Frequency = (Number of Oscillations)/Time = 40/4 = 10 Hz
The time required to complete one oscillation is known as time period. It is given by the
inverse of the frequency.
Time period = 1/(Frequency of Oscillation) = 1/10 = 0.1 sec.
Q6 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. The time required to complete one oscillation is known as time period.
It is given by the inverse of the frequency.
Time period = 1/(Frequency of Oscillation)
Frequency of oscillations = 500 Hz
Time period = 1/500 = .002 s
Q7 Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
Answer. (a) Dholak is a musical instrument. It consists of a stretched membrane called
its head. When the head is beaten gently, the stretched membrane sets into vibration.
Since sound is produced when an object vibrates, the dholak produces a sound.
(b) Sitar is a musical instrument. It consists of stretched strings. When a string is
plucked, it sets into vibration. Since sound is produced when an object vibrates, the sitar
produces a sound.
(c) Flute is a hollow pipe. When air is blown over its mouth, the air inside the pipe is set
Page 3 of 6 Aglasem Schools
(d) Unwanted sound is called __noise__.
(e) Shrillness of a sound is determined by the __frequency__ of vibration.
(Shrillness is also called pitch of the sound. Pitch is directly proportional to the
frequency of vibration. Hence, shrillness is determined by the frequency of vibration.)
Q5 A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer. Frequency of oscillations is de�ned as the number of oscillations of a vibrating
body per second. It is given by
Frequency = (Number of Oscillations)/Time = 40/4 = 10 Hz
The time required to complete one oscillation is known as time period. It is given by the
inverse of the frequency.
Time period = 1/(Frequency of Oscillation) = 1/10 = 0.1 sec.
Q6 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. The time required to complete one oscillation is known as time period.
It is given by the inverse of the frequency.
Time period = 1/(Frequency of Oscillation)
Frequency of oscillations = 500 Hz
Time period = 1/500 = .002 s
Q7 Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
Answer. (a) Dholak is a musical instrument. It consists of a stretched membrane called
its head. When the head is beaten gently, the stretched membrane sets into vibration.
Since sound is produced when an object vibrates, the dholak produces a sound.
(b) Sitar is a musical instrument. It consists of stretched strings. When a string is
plucked, it sets into vibration. Since sound is produced when an object vibrates, the sitar
produces a sound.
(c) Flute is a hollow pipe. When air is blown over its mouth, the air inside the pipe is set
Page 3 of 6 Aglasem Schools
Page 5
Book : Science Ncert Solutions | Chapter-13 Science
into vibration. As a result, a pleasant sound is produced.
Q8 What is the difference between noise and music? Can music become noise
sometimes?
Answer. The sound that is pleasing to the ear is called music. For example, the sound
produced by violins, pianos, �utes, pungs, etc.
The sound that is unpleasing to the ear is called noise.
Some examples of noise are as follows:
(i) Sound produced by horns of buses and trucks
(ii) Sound of electrical generators
(iii) Sound of a gun shot
(iv) Sound produced by jackhammers
Yes. Music can become noise when played at high volumes.
Q9 List sources of noise pollution in your surroundings.
Answer. Some sources of noise pollution are as follows:
(i) Televisions and transistors running at high volumes
(ii) Loudspeakers and crackers
(iii) Horns of buses, cars and trucks
(iv) Home appliances such as mixer, desert cooler, etc.
Q10 Explain in what way noise pollution is harmful to human.
Answer. Noise pollution can lead to a number of health-related problems. Some of them
are as follows:
(i) Hearing loss
(ii) Insomnia; inability to sleep
(iii) Hypertension
(iv) Severe headache
(v) Stress
Page 4 of 6 Aglasem Schools
into vibration. As a result, a pleasant sound is produced.
Q8 What is the difference between noise and music? Can music become noise
sometimes?
Answer. The sound that is pleasing to the ear is called music. For example, the sound
produced by violins, pianos, �utes, pungs, etc.
The sound that is unpleasing to the ear is called noise.
Some examples of noise are as follows:
(i) Sound produced by horns of buses and trucks
(ii) Sound of electrical generators
(iii) Sound of a gun shot
(iv) Sound produced by jackhammers
Yes. Music can become noise when played at high volumes.
Q9 List sources of noise pollution in your surroundings.
Answer. Some sources of noise pollution are as follows:
(i) Televisions and transistors running at high volumes
(ii) Loudspeakers and crackers
(iii) Horns of buses, cars and trucks
(iv) Home appliances such as mixer, desert cooler, etc.
Q10 Explain in what way noise pollution is harmful to human.
Answer. Noise pollution can lead to a number of health-related problems. Some of them
are as follows:
(i) Hearing loss
(ii) Insomnia; inability to sleep
(iii) Hypertension
(iv) Severe headache
(v) Stress
Page 4 of 6 Aglasem Schools
Page 6
Book : Science Ncert Solutions | Chapter-13 Science
Q11 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. There will be more noise in the house which is along the roadside. This is
because noise produced by transportation vehicles may cause trouble to the residents.
The intensity of noise decreases with the distance between the source and the listener.
Hence, it is better to take the house that is three lanes away from the roadside.
Q12 Sketch larynx and explain its function in your own words.
Answer. Larynx is a part of the throat. It is responsible for production of sound. A sketch
of a human larynx is shown in the following �gure.
Larynx moves when we swallow something. Inside the larynx, there are two vocal cords.
There is a small gap between them. This small gap allows air to pass through.
When we speak, air is forced into this small gap by the lungs. This prompts vocal cords to
vibrate. Since vibrating objects produce sound, sound is produced due to the vibration of
vocal cords.
Q13 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 speed of light is more than the speed of sound. Therefore, even though
thunder and lightning take place simultaneously, we see the lightning earlier.
Page 5 of 6 Aglasem Schools
Q11 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. There will be more noise in the house which is along the roadside. This is
because noise produced by transportation vehicles may cause trouble to the residents.
The intensity of noise decreases with the distance between the source and the listener.
Hence, it is better to take the house that is three lanes away from the roadside.
Q12 Sketch larynx and explain its function in your own words.
Answer. Larynx is a part of the throat. It is responsible for production of sound. A sketch
of a human larynx is shown in the following �gure.
Larynx moves when we swallow something. Inside the larynx, there are two vocal cords.
There is a small gap between them. This small gap allows air to pass through.
When we speak, air is forced into this small gap by the lungs. This prompts vocal cords to
vibrate. Since vibrating objects produce sound, sound is produced due to the vibration of
vocal cords.
Q13 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 speed of light is more than the speed of sound. Therefore, even though
thunder and lightning take place simultaneously, we see the lightning earlier.
Page 5 of 6 Aglasem Schools
Page 7
Book : Science Ncert Solutions | Chapter-13 Science
Page 6 of 6 Aglasem Schools
Page 6 of 6 Aglasem Schools
Document Details
| Board / Org | NCERT |
| Exam | Class 8 |
| Type | Solution |
| Pages | 7 |
| Language | english |
| Updated | 22 Jul 2026 |