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

9th Grade > Physics

SOUND MCQs

Total Questions : 57 | Page 1 of 6 pages

Question 1. A ship sends out ultrasound that return from the seabed and is detected after

5 s

. If the speed of ultrasound through seawater is

1600 m s^{- 1}

, what is the distance of the seabed from the ship?

2.5 km
3.5 km
4 km
5 km

Discuss Question

Answer: Option C. -> 4 km
:
C
Given:
Speed of ultrasound in seawater,

v = 1600 m s^{- 1}

Time for sound to travel from ship to seabed and then back,

t = 5 s

Letthe distance between ship and seabed be

d

.
The totaldistance travelled by the sound waves will be

2 d

.
Distance travelled by the wave is the product ofspeed and time.

2 d = v t = 1600 \times 5 = 8000 m

d = \frac{8000}{2} = 4000 m = 4 k m

Hence, the distance of seabed from ship is

4 k m

Question 2. Ocean wave is an example of a longitudinal wave.

True
False

Discuss Question

Answer: Option B. -> False
:
B

Ocean Wave Is An Example Of A Longitudinal wave.

Longitudinal waves are the type of waves in which the particles vibrate along the direction of propagation of wave. Transverse waves are those inwhich the particles vibrate perpendicular to the direction of propagation of wave. In case of ocean waves, the particles vibrate perpendicular to the direction of propagation of wave, soit is a transverse wave.

Question 3. The loudness of sound depends upon _______.

amplitude
wavelength
time period
frequency

Discuss Question

Answer: Option A. -> amplitude
:
A
Loudness determines the magnitude of the auditory sensation produced.More the intensity of sound wave, more is the loudness. Intensity of the sound wave depends on the energy per unit volume in the wave. Energy itself is proportional to the (square of) amplitude of the wave.

Question 4. 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 5. 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. Thereforesound cannot travel in outer space. This is the reason why people cannot talk to each other in vacuum.

Question 6. 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 7. Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called:

SONAR
RADAR
Ultrasonography
Electrocardiography

Discuss Question

Answer: Option D. -> Electrocardiography
:
D
In electrocardiography (also known as ECG or EKG), ultrasonic waves are made to reflect from various parts of the heart and an image of the heart is produced. For this, electrodes are placed on the skin of the limbs and chest. It helps to understand the irregularities in heart rythm.

Question 8. What is the relationship between wavelength and frequency in a given medium?

Wavelength is directly proportional to frequency
Wavelength is inversely proportional to frequency
Frequency is twice the wavelength
Wavelength is twice the frequency

Discuss Question

Answer: Option B. -> Wavelength is inversely proportional to frequency
:
B

λ = \frac{v}{f}

where:

λ :

Wavelength

f :

Frequency

v :

Speed of light in the given medium
In a medium, speed is constant.

⟹ λ \propto \frac{1}{f}

Hence, wavelength is inversely proportional to frequency in a medium.

Question 9. A sound wave having a wavelength of

2 c m

is travelling in water. If the velocity of sound in water is

1600 m s^{- 1}

. What is the frequency of the sound wave?

8000 Hz
80000 Hz
70000 Hz
16000 Hz

Discuss Question

Answer: Option B. -> 80000 Hz
:
B
Given:
Speed of sound wave,

v = 1600 m s^{- 1}

Wavelength,

λ = 2 c m = 0.02 m

Let

f

be the frequency of the wave.
Speed of sound is given by:

v = f λ

f = \frac{1600 m s^{- 1}}{0.02 m} = 80000 H z .

Frequency of the sound wave is

80000 H z

Question 10. When a drum is beaten, a sound is heard due to ___.

heating of the membrane
vibration of the membrane
both heating and vibration of the membrane
freezing of the membrane

Discuss Question

Answer: Option B. -> vibration of the membrane
:
B
When a drum is beaten, the membrane of the drum vibrates which can be felt by touching it and the sound is heard. As the membrane stops vibrating, no sound is heard. The vibrating drum produces sound.