Selina solutions concise physics class 9 icse Solutions for Chapter 8 chapter 8 propogation of sound waves

Exercises in Chapter 8 chapter 8 propogation of sound waves Grade 9

Exercise 8A

Exercise 8B

Questions in Exercise 8A

What causes sound?

What is sound? How is it produced

Complete the following sentence:

Sound is produced by a ____________ body

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

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

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

State three characteristics of the medium required for propagation of sound in a medium.

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

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) travels in form of a wave

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

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

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

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

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

Describe an experiment to show that in a wave motion, only energy is transferred, but particles of medium do not leave their positions

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

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

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

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

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

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

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

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

Arrange the speed of sound in gases Vg, solids Vs, and liquids Vl in an ascending order

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

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

Answer the following:

(i) Can sound travel in a vacuum?

(ii) How does the speed of sound different in different media?

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

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

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

diver 100m below the point of explosion.

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

(ii) Give a reason for your answer in part (i)

(iii) If sound takes time t to reach the boat man, how much time approximately does it take

to reach the diver

How do the following factors affect, if at all, the speed of sound in air:

(i) Frequency of air

(ii) Temperature of air

(iii) Pressure of air

(iv) Moisture in air?

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

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

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

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

Complete the following sentences:

(a) Sound cannot travel through _________ but it requires a _____________

(b) When sound travels in a medium, the particles of medium __________ but the disturbance

(c) A longitudinal wave is composed of compression and _____________

(d) A transverse wave is composed of crest and _____________

(e) Wave velocity = ____________ x wavelength

The correct statement is:

(a) Sound and light both require a medium for propagation

(b) Sound can travel in a vacuum, but light cannot

(c) Sound needs a medium, but light does not need a medium for its propagation

(d) Sound and light both can travel in vaccum

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

(a) 1450 m/s

(b) 450 m/s

(c) 5100 m/s

(d) 330 m/s

Sound in air propagates in form of:

(a) Longitudinal wave

(b) Transverse wave

(c) Both longitudinal and transverse wave

(d) Neither longitudinal nor transverse wave

The speed of light in air is:

(a) 3 x 108 m/s

(b) 330 m/s

(c) 5100 m/s

(d) 3 x 1010 m/s

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

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

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

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

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

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

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

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 is 340m/s, find the distance between the boys.

An observer sitting in a 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

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

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

Questions in Exercise 8B

What do you mean by the audible range of frequency

What is the audible range of frequency for humans

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

Which has the higher frequency – ultrasonic sound or infrasonic sound

(a) An average person can hear sound of frequencies in the range ___________ to

___

(b) Ultrasound is of frequency ____________

(c) Infrasonic sound is of frequency ___________

(d) Bats can produce and hear ___________ sound

(e) Elephants produce ____________ sound

Name the sounds of the frequencies given below: