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 Page 1


Sound 
Points to Remember 
?  Sound is a form of energy which produces the sensation of hearing. 
?  Sound requires a medium to travel. It cannot travel in vacuum. 
?  Sound travels in all directions. Sound can travel through solids, liquids and gases. 
?  Sound travels faster in solids than in liquids and gases. 
?  The loudness of sound is measured on a special scale called the decibel scale. 
?  Sound is classified into two groups. (i) Musical sound, (ii) Noise. 
?  Musical sound is produced by periodic vibrations. 
?  Noise is produced by non-periodic motions. 
?  What the sound gets repeated after reflection from a distant body, is called an 
echo. 
?  Multiple echoes are called reverberations. 
?  Sonar is method used to measure the depth of a sea and is based on the 
principle of echo. 
?  Music is pleasent to hear and is caused by periodic vibrations. 
?  Noise is irritating and is produced by an irregular pattern of waves. 
?  The three characteristics of sound are loudness, pitch, quality or timbre. 
?  Loudness depends upon many factors, e.g. amplitude, distance, waves of 
vibrating body, humidity, pressure, wind velocity etc. 
?  Pitch depends on the frequency of sound. Higher is the pitch, shriller is the sound. 
?  Loudness is merely a sensation. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) Sound can travel in vacuum. 
Answer. False. 
Correct — Sound requires medium to travel. 
(b) Sound is a form of energy. 
Answer. True. 
(c) Sound can only be produced by vibrating bodies. 
Answer. True. 
Page 2


Sound 
Points to Remember 
?  Sound is a form of energy which produces the sensation of hearing. 
?  Sound requires a medium to travel. It cannot travel in vacuum. 
?  Sound travels in all directions. Sound can travel through solids, liquids and gases. 
?  Sound travels faster in solids than in liquids and gases. 
?  The loudness of sound is measured on a special scale called the decibel scale. 
?  Sound is classified into two groups. (i) Musical sound, (ii) Noise. 
?  Musical sound is produced by periodic vibrations. 
?  Noise is produced by non-periodic motions. 
?  What the sound gets repeated after reflection from a distant body, is called an 
echo. 
?  Multiple echoes are called reverberations. 
?  Sonar is method used to measure the depth of a sea and is based on the 
principle of echo. 
?  Music is pleasent to hear and is caused by periodic vibrations. 
?  Noise is irritating and is produced by an irregular pattern of waves. 
?  The three characteristics of sound are loudness, pitch, quality or timbre. 
?  Loudness depends upon many factors, e.g. amplitude, distance, waves of 
vibrating body, humidity, pressure, wind velocity etc. 
?  Pitch depends on the frequency of sound. Higher is the pitch, shriller is the sound. 
?  Loudness is merely a sensation. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) Sound can travel in vacuum. 
Answer. False. 
Correct — Sound requires medium to travel. 
(b) Sound is a form of energy. 
Answer. True. 
(c) Sound can only be produced by vibrating bodies. 
Answer. True. 
(d) Larger is the amplitude, feeble is the sound. 
Answer.False. 
Correct — Larger the amplitude, greater is the sound. 
(e) The frequency is measured in hertz. 
Answer. True. 
(f) Loudness depends on frequency. 
Answer. False. 
Correct — Loudness depends on the amplitude. 
(g) Waveforms of two different stringed instruments can be the same. 
Answer. False. 
Correct—Waveforms of two different stringed instruments cannot be the same. 
(h) Female voice is shriller than the male voice. 
Answer. True. 
(i) A ticking clock sound is heard late when heard through a metal. 
Answer. False. 
Correct—A ticking clock sounds is heard early when heard through a metal. 
2. Fill in the blanks 
(a) Sound is produced when a body vibrates. 
(b) The number of times a body vibrates in one second is called its frequency. 
(c) The pitch of a sound depends on its frequency. 
(d) Sound can travel in a medium solid, liquid or gas. 
(e) We can hear sounds of frequency in the range of 20 Hz to 20,000 Hz. 
(f) Sound requires a medium for propagation. 
(g) Sound travels faster in solids than in liquids. 
(h) The sound heard after reflection is echo. 
(i) Sound produces sensation in ears. 
 
 
 
 
Page 3


Sound 
Points to Remember 
?  Sound is a form of energy which produces the sensation of hearing. 
?  Sound requires a medium to travel. It cannot travel in vacuum. 
?  Sound travels in all directions. Sound can travel through solids, liquids and gases. 
?  Sound travels faster in solids than in liquids and gases. 
?  The loudness of sound is measured on a special scale called the decibel scale. 
?  Sound is classified into two groups. (i) Musical sound, (ii) Noise. 
?  Musical sound is produced by periodic vibrations. 
?  Noise is produced by non-periodic motions. 
?  What the sound gets repeated after reflection from a distant body, is called an 
echo. 
?  Multiple echoes are called reverberations. 
?  Sonar is method used to measure the depth of a sea and is based on the 
principle of echo. 
?  Music is pleasent to hear and is caused by periodic vibrations. 
?  Noise is irritating and is produced by an irregular pattern of waves. 
?  The three characteristics of sound are loudness, pitch, quality or timbre. 
?  Loudness depends upon many factors, e.g. amplitude, distance, waves of 
vibrating body, humidity, pressure, wind velocity etc. 
?  Pitch depends on the frequency of sound. Higher is the pitch, shriller is the sound. 
?  Loudness is merely a sensation. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) Sound can travel in vacuum. 
Answer. False. 
Correct — Sound requires medium to travel. 
(b) Sound is a form of energy. 
Answer. True. 
(c) Sound can only be produced by vibrating bodies. 
Answer. True. 
(d) Larger is the amplitude, feeble is the sound. 
Answer.False. 
Correct — Larger the amplitude, greater is the sound. 
(e) The frequency is measured in hertz. 
Answer. True. 
(f) Loudness depends on frequency. 
Answer. False. 
Correct — Loudness depends on the amplitude. 
(g) Waveforms of two different stringed instruments can be the same. 
Answer. False. 
Correct—Waveforms of two different stringed instruments cannot be the same. 
(h) Female voice is shriller than the male voice. 
Answer. True. 
(i) A ticking clock sound is heard late when heard through a metal. 
Answer. False. 
Correct—A ticking clock sounds is heard early when heard through a metal. 
2. Fill in the blanks 
(a) Sound is produced when a body vibrates. 
(b) The number of times a body vibrates in one second is called its frequency. 
(c) The pitch of a sound depends on its frequency. 
(d) Sound can travel in a medium solid, liquid or gas. 
(e) We can hear sounds of frequency in the range of 20 Hz to 20,000 Hz. 
(f) Sound requires a medium for propagation. 
(g) Sound travels faster in solids than in liquids. 
(h) The sound heard after reflection is echo. 
(i) Sound produces sensation in ears. 
 
 
 
 
3. Match the following 
 
4. Select the correct alternative  
(a) We can distinguish a shrill sound from a flat sound by its 
1.  amplitude 
2.  loudness 
3.  pitch 
4.  none of the above. 
(b) We can hear sound of frequency 
1.  10 Hz 
2.  500 Hz 
3.  100,000 Hz 
4.  50,000 Hz 
(c) Sound cannot travel in 
1.  gases 
Page 4


Sound 
Points to Remember 
?  Sound is a form of energy which produces the sensation of hearing. 
?  Sound requires a medium to travel. It cannot travel in vacuum. 
?  Sound travels in all directions. Sound can travel through solids, liquids and gases. 
?  Sound travels faster in solids than in liquids and gases. 
?  The loudness of sound is measured on a special scale called the decibel scale. 
?  Sound is classified into two groups. (i) Musical sound, (ii) Noise. 
?  Musical sound is produced by periodic vibrations. 
?  Noise is produced by non-periodic motions. 
?  What the sound gets repeated after reflection from a distant body, is called an 
echo. 
?  Multiple echoes are called reverberations. 
?  Sonar is method used to measure the depth of a sea and is based on the 
principle of echo. 
?  Music is pleasent to hear and is caused by periodic vibrations. 
?  Noise is irritating and is produced by an irregular pattern of waves. 
?  The three characteristics of sound are loudness, pitch, quality or timbre. 
?  Loudness depends upon many factors, e.g. amplitude, distance, waves of 
vibrating body, humidity, pressure, wind velocity etc. 
?  Pitch depends on the frequency of sound. Higher is the pitch, shriller is the sound. 
?  Loudness is merely a sensation. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) Sound can travel in vacuum. 
Answer. False. 
Correct — Sound requires medium to travel. 
(b) Sound is a form of energy. 
Answer. True. 
(c) Sound can only be produced by vibrating bodies. 
Answer. True. 
(d) Larger is the amplitude, feeble is the sound. 
Answer.False. 
Correct — Larger the amplitude, greater is the sound. 
(e) The frequency is measured in hertz. 
Answer. True. 
(f) Loudness depends on frequency. 
Answer. False. 
Correct — Loudness depends on the amplitude. 
(g) Waveforms of two different stringed instruments can be the same. 
Answer. False. 
Correct—Waveforms of two different stringed instruments cannot be the same. 
(h) Female voice is shriller than the male voice. 
Answer. True. 
(i) A ticking clock sound is heard late when heard through a metal. 
Answer. False. 
Correct—A ticking clock sounds is heard early when heard through a metal. 
2. Fill in the blanks 
(a) Sound is produced when a body vibrates. 
(b) The number of times a body vibrates in one second is called its frequency. 
(c) The pitch of a sound depends on its frequency. 
(d) Sound can travel in a medium solid, liquid or gas. 
(e) We can hear sounds of frequency in the range of 20 Hz to 20,000 Hz. 
(f) Sound requires a medium for propagation. 
(g) Sound travels faster in solids than in liquids. 
(h) The sound heard after reflection is echo. 
(i) Sound produces sensation in ears. 
 
 
 
 
3. Match the following 
 
4. Select the correct alternative  
(a) We can distinguish a shrill sound from a flat sound by its 
1.  amplitude 
2.  loudness 
3.  pitch 
4.  none of the above. 
(b) We can hear sound of frequency 
1.  10 Hz 
2.  500 Hz 
3.  100,000 Hz 
4.  50,000 Hz 
(c) Sound cannot travel in 
1.  gases 
2.  liquids 
3.  solids 
4.  vacuum 
(d) The minimum distance required between the source and the reflector so as to hear 
the echo in air is 
1.  10m 
2. 17m 
3.  34 m 
4.  50 m 
(e) Wavelength is measured in 
1.  kg 
2.  second 
3.  litre 
4. metre 
(f) The speed of sound in water is 
1.  332 m 
2. 1500 m 
3.  5000 m s 
4.  1000 m s 
(g) Sound travels the fastest in 
1.  liquids 
2.  solids 
3.  gases 
4.  vacuum 
B. Short/Long Answer Questions 
Question 1. 
What do you mean by a vibratory motion ? 
Answer: 
The oscillatory motion in which the body assumes a new shape during its motion, is 
called the vibratory motion. 
 
Page 5


Sound 
Points to Remember 
?  Sound is a form of energy which produces the sensation of hearing. 
?  Sound requires a medium to travel. It cannot travel in vacuum. 
?  Sound travels in all directions. Sound can travel through solids, liquids and gases. 
?  Sound travels faster in solids than in liquids and gases. 
?  The loudness of sound is measured on a special scale called the decibel scale. 
?  Sound is classified into two groups. (i) Musical sound, (ii) Noise. 
?  Musical sound is produced by periodic vibrations. 
?  Noise is produced by non-periodic motions. 
?  What the sound gets repeated after reflection from a distant body, is called an 
echo. 
?  Multiple echoes are called reverberations. 
?  Sonar is method used to measure the depth of a sea and is based on the 
principle of echo. 
?  Music is pleasent to hear and is caused by periodic vibrations. 
?  Noise is irritating and is produced by an irregular pattern of waves. 
?  The three characteristics of sound are loudness, pitch, quality or timbre. 
?  Loudness depends upon many factors, e.g. amplitude, distance, waves of 
vibrating body, humidity, pressure, wind velocity etc. 
?  Pitch depends on the frequency of sound. Higher is the pitch, shriller is the sound. 
?  Loudness is merely a sensation. 
Test Yourself 
A. Objective Questions  
1. Write true or false for each statement 
(a) Sound can travel in vacuum. 
Answer. False. 
Correct — Sound requires medium to travel. 
(b) Sound is a form of energy. 
Answer. True. 
(c) Sound can only be produced by vibrating bodies. 
Answer. True. 
(d) Larger is the amplitude, feeble is the sound. 
Answer.False. 
Correct — Larger the amplitude, greater is the sound. 
(e) The frequency is measured in hertz. 
Answer. True. 
(f) Loudness depends on frequency. 
Answer. False. 
Correct — Loudness depends on the amplitude. 
(g) Waveforms of two different stringed instruments can be the same. 
Answer. False. 
Correct—Waveforms of two different stringed instruments cannot be the same. 
(h) Female voice is shriller than the male voice. 
Answer. True. 
(i) A ticking clock sound is heard late when heard through a metal. 
Answer. False. 
Correct—A ticking clock sounds is heard early when heard through a metal. 
2. Fill in the blanks 
(a) Sound is produced when a body vibrates. 
(b) The number of times a body vibrates in one second is called its frequency. 
(c) The pitch of a sound depends on its frequency. 
(d) Sound can travel in a medium solid, liquid or gas. 
(e) We can hear sounds of frequency in the range of 20 Hz to 20,000 Hz. 
(f) Sound requires a medium for propagation. 
(g) Sound travels faster in solids than in liquids. 
(h) The sound heard after reflection is echo. 
(i) Sound produces sensation in ears. 
 
 
 
 
3. Match the following 
 
4. Select the correct alternative  
(a) We can distinguish a shrill sound from a flat sound by its 
1.  amplitude 
2.  loudness 
3.  pitch 
4.  none of the above. 
(b) We can hear sound of frequency 
1.  10 Hz 
2.  500 Hz 
3.  100,000 Hz 
4.  50,000 Hz 
(c) Sound cannot travel in 
1.  gases 
2.  liquids 
3.  solids 
4.  vacuum 
(d) The minimum distance required between the source and the reflector so as to hear 
the echo in air is 
1.  10m 
2. 17m 
3.  34 m 
4.  50 m 
(e) Wavelength is measured in 
1.  kg 
2.  second 
3.  litre 
4. metre 
(f) The speed of sound in water is 
1.  332 m 
2. 1500 m 
3.  5000 m s 
4.  1000 m s 
(g) Sound travels the fastest in 
1.  liquids 
2.  solids 
3.  gases 
4.  vacuum 
B. Short/Long Answer Questions 
Question 1. 
What do you mean by a vibratory motion ? 
Answer: 
The oscillatory motion in which the body assumes a new shape during its motion, is 
called the vibratory motion. 
 
Question 2. 
What is sound ? 
Answer: 
Sound is a form of energy which produces the sensation of hearing. 
Question 3. 
How is sound produced ? 
Answer: 
Sound is produced by vibrating bodies. 
Question 4. 
Describe an experiment to show that each source of sound is a vibrating body. 
Answer: 
Sound is produced when a body vibrates. In other words, each source of sound is a 
vibrating body. This can be demonstrated by the following experiment. 
Take a ruler. Press its one end on the table with the left hand as shown in figure. Pull 
down the other end of the ruler with the right hand and then leave it. 
You will notice that the ruler vibrates i.e., the ruler moves to and fro and a humming 
sound is heard. 
After some time, the ruler stops vibrating. No sound is then heard. 
 
This shows that the humming sound is produced only because of the vibrations of the 
ruler. 
Question 5. 
Name two sources of sound. 
Answer: 
Each vibrating body is a source of sound. We, the human beings, produce sound when 
our vocal cords vibrate on blowing air through them by our lungs. Some animals like 
birds, frogs etc., also produce sound due to vibration of their vocal cords. But bees do 
not have the voice-boxes. They produce sound by moving their wings up and down very 
fast.

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FAQs on Selina Textbook Solutions: Sound - Physics Class 7 ICSE

1. What is sound and how is it produced?

Ans. Sound is a form of energy that is produced by vibrating objects. When an object vibrates, it creates pressure waves in the air (or any medium), which our ears detect as sound. For example, when a guitar string is plucked, it vibrates and produces sound waves that travel through the air.

2. How does sound travel through different mediums?

Ans. Sound travels through different mediums such as solids, liquids, and gases, but it travels fastest in solids. This is because the particles in solids are closely packed, allowing vibrations to transfer quickly. In liquids, particles are less tightly packed than in solids, so sound travels slower. In gases, the particles are far apart, making sound travel the slowest.

3. What are the characteristics of sound?

Ans. The main characteristics of sound include pitch, loudness, and quality (or timbre). Pitch refers to how high or low a sound is, which is determined by the frequency of the sound waves. Loudness is related to the amplitude of the waves; higher amplitude means a louder sound. Quality refers to the unique sound that distinguishes one source from another, even if they produce the same pitch and loudness.

4. Why do we hear echoes and how are they formed?

Ans. Echoes occur when sound waves reflect off a surface and return to our ears. This happens when the sound waves hit a hard surface, such as a wall or a mountain. The time taken for the sound to travel to the surface and back determines how we perceive the echo. If the reflected sound reaches our ears after a delay of about 0.1 seconds, we can hear it as a distinct echo.

5. What is the difference between noise and music?

Ans. The difference between noise and music lies in their organization and harmony. Music is a structured arrangement of sounds that are pleasing to the ear, typically with melody and rhythm. Noise, on the other hand, consists of random, chaotic sounds that do not have a specific pattern or harmony. While music can evoke emotions and feelings, noise is often considered unpleasant or disruptive.

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