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# Selina solutions for Concise Physics Class 9 ICSE chapter 8 - Propagation of Sound Waves [Latest edition]

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## Chapter 8: Propagation of Sound Waves

Exercise - 8(A)Exercise - 8(B)Exercise - 8(C)Others

### Selina solutions for Concise Physics Class 9 ICSE Chapter 8 Propagation of Sound Waves Exercise - 8(A) [Pages 182 - 183]

Exercise - 8(A) | Q 1 | Page 182

What causes sound?

Exercise - 8(A) | Q 2 | Page 182

What is sound? How is it produced?

Exercise - 8(A) | Q 3 | Page 182

Complete the following sentence :

Sound is produced by a ___________ body.

Exercise - 8(A) | Q 4 | Page 182

Describe a simple experiment which demonstrates that the sound produced by a tuning fork is due to vibrations of its arms.

Exercise - 8(A) | Q 5 | Page 182

Describe in brief, with the aid of a lebelled diagram, an experiment to demonstrate that a material medium is necessary for propagation of sound.

Exercise - 8(A) | Q 6 | Page 182

There is no atmosphere on moon. Can you hear each other on the moon's surface?

Exercise - 8(A) | Q 7 | Page 182

State three characteristics of the medium required for propagation of sound?

Exercise - 8(A) | Q 8 | Page 182

Explain with an example, the propagation of sound in a medium.

Exercise - 8(A) | Q 9 | Page 182

Choose the correct word/words to complete the following sentence :

When sound travels in a medium ____________

• the particles of the medium

• the source

• the disturbance

• the medium

Exercise - 8(A) | Q 10 | Page 182

Name the two kinds of waves in form of which sound travels in a medium.

Exercise - 8(A) | Q 11 | Page 182

What is a longitudinal wave? In which medium: solid, liquid or gas, can it be produced?

Exercise - 8(A) | Q 12 | Page 182

What is a transverse wave? In which medium: solid, liquid or gas, can it be produced?

Exercise - 8(A) | Q 13 | Page 182

Explain meaning of the terms compression and rarefaction in relation to a longitudinal wave.

Exercise - 8(A) | Q 14 | Page 182

Explain the terms crest and trough in relation to a transverse wave.

Exercise - 8(A) | Q 15 | Page 182

Describe an experiment to show that in wave motion, only energy is transferred, but particles of medium do not move.

Exercise - 8(A) | Q 16 | Page 182

Define the term amplitude of a wave. Write its S.I. unit.

Exercise - 8(A) | Q 17 | Page 182

What do you mean by the term frequency of a wave? State its S.I. unit.

Exercise - 8(A) | Q 18 | Page 182

How is the frequency of a wave related to its time period?

Exercise - 8(A) | Q 19 | Page 182

Define the term wave velocity. Write its S.I. unit.

Exercise - 8(A) | Q 20 | Page 182

Draw displacement-time graph of a wave and show on it the amplitude and time period of wave.

Exercise - 8(A) | Q 21 | Page 182

Draw a displacement-distance graph of a wave and mark on it, the amplitude of wave by the letter 'a' and wavelength of wave by the letter λ.

Exercise - 8(A) | Q 22 | Page 182

How are the wave velocity V, frequency f and wavelength λ of a wave related? Derive the relationship.

Exercise - 8(A) | Q 23 | Page 182

State two properties of medium on which the speed of sound in it depends.

Exercise - 8(A) | Q 24 | Page 182

Arrange the speed of sound in gases Vgsolids Vs and liquids VLin an ascending order.

Exercise - 8(A) | Q 25 | Page 182

State the speed of (i) light and (ii) sound in air?

Exercise - 8(A) | Q 26 | Page 182

Compare approximately the speed of sound in air, water and steel.

Exercise - 8(A) | Q 27.1 | Page 182

Can sound travel in vacuum?

Exercise - 8(A) | Q 27.2 | Page 182

How does the speed of sound differ in different media?

Exercise - 8(A) | Q 28 | Page 182

Flash of lightning reaches earlier than the sound of thunder. Explain the reason.

Exercise - 8(A) | Q 29 | Page 182

If you place your ear close to an iron railing which is tapped some distance away, you hear the sound twice. Explain why?

Exercise - 8(A) | Q 30 | Page 182

The sound of an explosion on the surface of a lake is heard by a boat man 100 m away and by a diver 100 m below the point of explosion.

(i) Who would hear the sound first: boatman or diver?

(iii) If sound takes time t to reach the boatman, how much time approximately does it take to reach the diver?

Exercise - 8(A) | Q 31.1 | Page 183

How does the following factor affect, if at all, the speed of sound in air:

Frequency of sound

Exercise - 8(A) | Q 31.2 | Page 183

How does the following factor affect, if at all, the speed of sound in air:

Temperature of air

Exercise - 8(A) | Q 31.3 | Page 183

How does the following factor affect, if at all, the speed of sound in air:

Pressure of air

Exercise - 8(A) | Q 31.4 | Page 183

How does the following factor affect, if at all, the speed of sound in air:

Moisture in air

Exercise - 8(A) | Q 32 | Page 183

How does the speed of sound change with change in (i) amplitude and (ii) wavelength, of sound wave?

Exercise - 8(A) | Q 33 | Page 183

In which medium the speed of sound is more: humid air or dry air? Give a reason to your answer.

Exercise - 8(A) | Q 34 | Page 183

How does the speed of sound in air vary with temperature?

Exercise - 8(A) | Q 35 | Page 183

Describe a simple experiment to determine the speed of sound in air. What approximation is made in the method described by you?

Exercise - 8(A) | Q 36.1 | Page 183

Complete the following sentences :

Sound cannot travel through __________, but it requires a ___________.

Exercise - 8(A) | Q 36.2 | Page 183

Complete the following sentences :

When sound travels in a medium, the particles of medium ___________ but the disturbance ___________.

Exercise - 8(A) | Q 36.3 | Page 183

Complete the following sentence :

A longitudinal wave is composed of  compression and ____________.

Exercise - 8(A) | Q 36.4 | Page 183

Complete the following sentence :

A transverse wave is composed of crest and ____________.

Exercise - 8(A) | Q 36.5 | Page 183

Complete the following sentences :

Wave velocity = ________________ × wavelength.

### Selina solutions for Concise Physics Class 9 ICSE Chapter 8 Propagation of Sound Waves Exercise - 8(A) [Page 183]

Exercise - 8(A) | Q 1 | Page 183

The correct statement is :

• Sound and light both require medium for propagation.

• Sound can travel in vacuum, but light can not

• Sound needs medium, but light does not need medium for its propagation.

• Sound and light both can travel in vacuum.

Exercise - 8(A) | Q 2 | Page 183

The speed of sound in air at 0°C is nearly :

• 1450 m s-1

• 450 m s-1

• 5100 m s-1

• 330 m s-1

Exercise - 8(A) | Q 3 | Page 183

Sound in air propagates in form of

• Longitudinal wave

• Transverse wave

• Both longitudinal and transverse waves

• Neither longitudinal nor transverse wave.

Exercise - 8(A) | Q 4 | Page 183

The speed of light in air is :

• 3 x 108 m s-1

• 330 m s-1

• 5100 m s-1

• 3 x 1010 m s-1

### Selina solutions for Concise Physics Class 9 ICSE Chapter 8 Propagation of Sound Waves Exercise - 8(A) [Page 183]

Exercise - 8(A) | Q 1 | Page 183

The heart of a man beats 75 times a minute. What is its (a) frequency and (b) time period?

Exercise - 8(A) | Q 2 | Page 183

The time period of a simple pendulum is 2 s. Find its frequency.

Exercise - 8(A) | Q 3 | Page 183

The separation between two consecutive crests in a transverse wave is 100 m. If wave velocity is 20 m s-1, find the frequency of wave.

Exercise - 8(A) | Q 4 | Page 183

A longitudinal wave travels at a speed of 0.3 m s-1 and the frequency of wave is 20 Hz. Find the separation between two consecutive compressions.

Exercise - 8(A) | Q 5 | Page 183

A source of wave produces 40 crests and 40 troughs in 0.4 s. What is the frequency of the wave?

Exercise - 8(A) | Q 6 | Page 183

An observer A fires a gun and another observer B at a distance 1650 m away from A hears its sound. If the speed of sound is 330 m s-1, find the time when B will hear the sound after firing by A.

Exercise - 8(A) | Q 7 | Page 183

The time interval between a lightning flash and the first sound of thunder was found to be 5 s. If the speed of sound in air is 330 m s-1, find the distance of flash from the observer.

Exercise - 8(A) | Q 8 | Page 183

A boy fires a gun and another boy at a distance hears the sound of fire 2.5s after seeing the flash. If the speed of sound in air 340 m/s, find distance between the boys.

Exercise - 8(A) | Q 9 | Page 183

An observer sitting in line of two tanks watches the flashes of two tanks firing at each other at the same time, but he hears the sounds of two shots 2s and 3.5s after seeing the flashes. If distance between the two tanks is 510m, find the speed of sound.

Exercise - 8(A) | Q 10 | Page 183

How long will sound take to travel in (a) and iron rail and (b) air, both 3.3 km in length? Take speed of sound in air to be 330 m/s and in iron to be 5280 m/s.

Exercise - 8(A) | Q 11 | Page 183

Assuming the speed of sound in air equal to 340 m/s and in water equal to 1360 m/s, find the time taken to travel a distance 1700 m by sound in (i) air (ii) water.

### Selina solutions for Concise Physics Class 9 ICSE Chapter 8 Propagation of Sound Waves Exercise - 8(B) [Page 185]

Exercise - 8(B) | Q 1 | Page 185

What do you mean by the audible range of frequency?

Exercise - 8(B) | Q 2 | Page 185

What is the audible range of frequency for human?

Exercise - 8(B) | Q 3 | Page 185

For which range of frequencies, human ears are most sensitive?

Exercise - 8(B) | Q 4 | Page 185

Which has the higher frequency - ultrasonic sound or infrasonic sound?

Exercise - 8(B) | Q 5.1 | Page 185

Complete the following sentences:

An average person can hear sound of frequencies in the range ______ to _________.

Exercise - 8(B) | Q 5.2 | Page 185

Complete the following sentence:

Ultrasound is of frequency ___________.

Exercise - 8(B) | Q 5.3 | Page 185

Complete the following sentence:

Infrasonic sound is of frequency ______________.

Exercise - 8(B) | Q 5.4 | Page 185

Complete the following sentence:

Bats can produce and hear ___________ sound.

Exercise - 8(B) | Q 5.5 | Page 185

Complete the following sentence:

Elephants produce ____________sound.

Exercise - 8(B) | Q 6.1 | Page 185

Name the sound of the frequency given below:

10 Hz

Exercise - 8(B) | Q 6.2 | Page 185

Name the sound of the frequency given below:

100 Hz

Exercise - 8(B) | Q 6.3 | Page 185

Name the sound of the frequency given below:

1000 Hz

Exercise - 8(B) | Q 6.4 | Page 185

Name the sound of the frequency given below:

40 kHz

Exercise - 8(B) | Q 7 | Page 185

Can you hear the sound produced due to vibrations of a seconds pendulum? Give reasons.

Exercise - 8(B) | Q 8 | Page 185

What is ultrasound?

Exercise - 8(B) | Q 9 | Page 185

State the approximate speed of ultrasound in air.

Exercise - 8(B) | Q 10 | Page 185

State two properties of ultrasound that make it useful to us.

Exercise - 8(B) | Q 11 | Page 185

Explain how do bats locate the obstacles and prey in their way.

Exercise - 8(B) | Q 12 | Page 185

State two applications of ultrasound.

### Selina solutions for Concise Physics Class 9 ICSE Chapter 8 Propagation of Sound Waves Exercise - 8(C) [Page 185]

Exercise - 8(C) | Q 1 | Page 185

A man can hear the sound of frequency :

• 1 Hz

• 1000 Hz

• 200 kHz

• 5 MHz

Exercise - 8(C) | Q 2 | Page 185

The properties of ultrasound that make it useful are

• High power and high speed

• High power and good directivity

• High frequency and high speed

• High frequency and bending around the objects.

Exercise - 8(C) | Q 3 | Page 185

Sonar makes use of :

• infrasonic sound

• ultrasound

• ordinary sound

• light

### Selina solutions for Concise Physics Class 9 ICSE Chapter 8 Propagation of Sound Waves

Which wave property determines (a) loudness, (b) pitch?

What are wavelength, frequency, time period and amplitude of a sound wave?

Guess which sound has a higher pitch: guitar or car horn?

Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.

A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?

Distinguish between loudness and intensity of sound.

Which characteristics of the sound helps you to identify your friend by his voice while sitting with others in a dark room?

The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

What is loudness of sound? What factors does it depend on?

## Chapter 8: Propagation of Sound Waves

Exercise - 8(A)Exercise - 8(B)Exercise - 8(C)Others

## Selina solutions for Concise Physics Class 9 ICSE chapter 8 - Propagation of Sound Waves

Selina solutions for Concise Physics Class 9 ICSE chapter 8 (Propagation of Sound Waves) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Concise Physics Class 9 ICSE solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Concise Physics Class 9 ICSE chapter 8 Propagation of Sound Waves are Nature of Sound Waves, Requirement of a Medium for Sound Waves to Travel, Propagation and Speed in Different Media, Comparison of Sound with Speed of Light, Thunder and Lightning, Infrasonic, Sonic, Ultrasonic Frequencies and Their Applications, Difference Between Ultrasonic and Supersonic, Measurements Using Common Instruments, Concept of Sound.

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