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

9th Grade > Physics

SOUND MCQs

Total Questions : 57 | Page 6 of 6 pages

The particles in a wave move at the same speed as the wave.

True
False
$400000 H z$
$633000 H z$

Discuss Question

Answer: Option B. -> False
:
B
The particles in a wave only oscillate about their position. They do not move at the speed of the wave, nor do they need to move in the same direction as that of the wave.

Question 52.

The cochlea of the ear converts pressure variations of the air into_____________.

electric signals
mechanical signals
magnetic signals
chemical signals

Discuss Question

Answer: Option A. -> electric signals
:
A

The cochlea of the ear converts pressure variations in the air (sound) into electric signals. These signals travel to the brain through auditory nerves, due to which we are able to hear it.

Question 53.

The wavelength of a sound wave is $40 c m$ and the time period is $0.0005 s$ . How many seconds will it take to travel a distance of $4 k m$ ?

$5 s$
$11 s$
$7 s$
$16 s$

Discuss Question

Answer: Option A. ->

5 s

:
A
Given:
Wavelength of sound wave,

λ = 40 c m = 0.4 m

Time period,

T = 0.0005 s

Distance travelled,

s = 4 k m = 4000 m

Let speed of sound wave be

v

.
Speed of a wave is the product will be:

v = \frac{λ}{T}

v = \frac{0.4 m}{0.0005 s}

v = 800 m s^{- 1}

Let the time taken for the wave to travel distance

s

t

.
From definition of speed,

v = \frac{s}{t}

t = \frac{s}{v}

t = \frac{4000}{800} = 5 s

Question 54.

A person is standing $1 k m$ away from a source of sound. The velocity of sound in the medium is $340 m s^{- 1}$ . Calculate the number of oscillations (approximately) that the sound wave makes before it reaches that person. The frequency of the sound is $500 H z$ .

1450
1417
1470
340

Discuss Question

Answer: Option C. -> 1470
:
C
Given:
Distance between source and observer,

s = 1000 m

Velocity of sound,

v = 340 m s^{- 1}

Frequency of sound,

f = 500 H z

Time taken for the sound wave to reach the observer from the source is:

t = \frac{s}{v}

Number of oscillations in

1 s

is the frequency,

f

Number of oscillations in time

t

will be:

n = t f

n = \frac{s}{v} f

n = \frac{1000 \times 500}{340}

n \approx 1470

Question 55.

Ultrasound can be used for which of the following purposes?

Echocardiography
Ultrasonography
MRI scan
Loudspeakers

Discuss Question

Answer: Option A. -> Echocardiography
:
A and B
A sound which has a frequency of 20,000 Hz or more, is called ultrasonic sound, or simply, ultrasound.
Ultrasonic sound waves are made to reflect from various parts of the heart, and form an image of the heart. This technique is called echocardiography.
Images of body organs are generated by sending ultrasonic sound through the tissues of human body. This is called ultrasonography.
MRI uses magnetic fields and radio waves to capture images of the organs.
Loudspeakers are devices that increases the amplitude of sound waves with the help of electrical energy.

Question 56.

The device which uses ultrasonic waves to measure the distance, direction and speed of underwater objects is:

SONAR
Ultrasonogram
RADAR
Ecocardiogram

Discuss Question

Answer: Option A. -> SONAR
:
A
The device which uses ultrasonic waves to measure the distance, direction and speed of underwater objects is known as SONAR. SONAR stands for Sound Navigation and Ranging.
It is used to find depth of the sea and to locate underwater hills, valleys, icebergs, sunken ships etc.
RADAR uses electromagnetic waves for echolocation. Also, it must be noted that RADAR is not useful underwater because electromagnetic waves die in water very quickly.

Question 57.

The maximum displacement of a particle from its mean position is called ___.