Sound(9th Grade > Physics ) Questions and answers for exam Preparation

9th Grade > Physics

SOUND MCQs

Total Questions : 57 | Page 5 of 6 pages

Which among the following statements is true?

Sound moves very slowly in the outer space.
Intensity of sound gets reduced in the outer space.
Shrillness of sound gets reduced in outer space.
Sound cannot propagate in outer space.

Discuss Question

Answer: Option D. -> Sound cannot propagate in outer space.
:
D
Sound needs a medium to travel, but outer space has no atmosphere. Therefore sound cannot travel in outer space. This is the reason why people cannot talk to each other in vacuum.

Question 42.

The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the _____

wavelength
amplitude
frequency
time period

Discuss Question

Answer: Option D. -> time period
:
D
The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave. The relation between time period 'T' and frequency 'F' is:

T = \frac{1}{F}

Question 43.

Particles in a longitudinal wave vibrate perpendicular to the direction of the wave propagation.

True
False
Shrillness of sound gets reduced in outer space.
Sound cannot propagate in outer space.

Discuss Question

Answer: Option B. -> False
:
B

Particles in a longitudinal wave oscillate along the direction of the wave propagation. Sound wave is an example of the longitudinal wave.

Question 44.

The time period of sound is increased by 4 times. Find the ratio of the new speed to the old speed.

Discuss Question

Answer: Option A. -> 1
:
A
Speed of sound in a medium is a characteristic of the medium and temperature.

v \propto \frac{\sqrt{T}}{\sqrt{ρ M}}

where:
v: Speed of sound
T: Temperature

ρ :

Density
M: Molecular Mass of the medium
Increasing time period decreases the frequency of the wave.

v = f λ

still holds because wavelength increases to maintain the speed of the wave in the medium.

Question 45.

A sound wave goes from medium A to medium B. What can you say about its frequency in both the mediums?

Frequency in A < Frequency in B
Frequency in A > Frequency in B
Frequency in A = Frequency in B
Insufficient data

Discuss Question

Answer: Option C. -> Frequency in A = Frequency in B
:
C

The frequency of sound waves depends only on the frequency of vibration of the source of sound. It does not depend on the medium of propogation. Thus, the frequency of sound in both media are same.

Question 46.

Sound waves are a sequence of compressions and _________ .

amplitudes
wavelengths
rarefactions
pitch

Discuss Question

Answer: Option C. -> rarefactions
:
C
Sound waves are a sequence of compressions and rarefactions. A compression is a region in a longitudinal wave where the particles are closer than normal. A rarefaction is a region in a longitudinal wave where the particles are farther than normal.

Question 47.

An observer stands at a distance of 850 m from the cliff and fires a gun. After what time gap will he hear the echo, if sound travels at a speed of $350 m s^{- 1}$ in air?

4.86 s
6.89 s
4.00 s
2.93 s

Discuss Question

Answer: Option A. -> 4.86 s
:
A
Given, speed of sound,

v = 350 m s^{- 1}

and distance between the observer and the cliff,

d = 850 m

.
This is a case of an echo, so distance travelled = 2d (because sound travels from the observer to the cliff and back to the observer)
We know,

s p e e d = \frac{d i s t a n c e}{t i m e}

v = \frac{2 d}{t}

\Rightarrow t = \frac{2 d}{v}

= \frac{(2 \times 850)}{350} = 4.86 s

Question 48.

The pitch of the sound depends on

frequency
pitch
intensity
amplitude

Discuss Question

Answer: Option A. -> frequency
:
A

The pitch of the sound depends only on frequency. More the frequency, more will be the pitch or shrillness of the voice.

Question 49.

Statement 1: No sound can be heard on the surface of the Moon.
Statement 2: High surface temperature of the Moon restricts sound propagation.

Only statement 1 is correct.
Only statement 2 is correct.
Both the statements are correct.
Both the statements are incorrect.

Discuss Question

Answer: Option A. -> Only statement 1 is correct.
:
A
Sound waves require a medium to travel. Due to the absence of atmosphere on the surface of the Moon, there is no medium for the sound to propagate. The propagation of sound on the Moon is not related to the surface temperature of the Moon. Also, the Moon's surface is very cold.
Thus, the statement 1 is correct, but the statement 2 is incorrect.

Question 50.

A sound is travelling in air at a speed of $343 m s^{- 1}$ . The wavelength of the sound wave is $0.1 c m$ . Find the frequency of the sound wave.