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

9th Grade > Physics

SOUND MCQs

Total Questions : 57 | Page 4 of 6 pages

Question 31.

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 32.

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?

$2.5 k m$
$3.5 k m$
$4 k m$
$5 k m$

Discuss Question

Answer: Option C. ->

4 k m

:
C

Given:
Speed of ultrasound in seawater, $v = 1600 m s^{- 1}$
Time for sound to travel from ship to seabed and then back, $t = 5 s$
Let the distance between ship and seabed be $d$ .
The total distance travelled by the sound waves will be $2 d$ .
Distance travelled by the wave is the product of speed 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 33.

Sound and light waves, both ______.

have the same speed
travel through vacuum
obey the laws of reflection
are forms of energy

Discuss Question

Answer: Option C. -> obey the laws of reflection
:
C and D
Both sound and light are forms of energy. Since sound waves are mechanical waves, they require a medium to propagate. Light waves do not require a medium to travel. Laws of reflection are applicable for both light and sound waves.
Speed of light and sound in air are

3 \times 10^{8} m s^{- 1}

and

340 m s^{- 1}

respectively.

Question 34.

If a person drops a pebble in a well of $100 m$ depth, after how much time (in seconds) will he be able to hear the sound?
Given:
Acceleration due to gravity, $g = 10 m s^{- 2}$
Speed of sound in air, $v = 343 m s^{- 1}$

$\sqrt{20} + 0.3 s$
$\sqrt{20} s$
$0.3 s$
$20 s$

Discuss Question

Answer: Option A. ->

\sqrt{20} + 0.3 s

:
A

The question can be divided into two parts, where in the first part, the time taken by the pebble to reach the bottom is calculated and in the second part, the time taken by the sound wave to reach the top is calculated.
Given:
Initial velocity, $u = 0 m s^{- 1}$
Depth of the well, $s = 100 m$
Acceleration, $a = 10 m s^{- 2}$
Speed of sound, $v = 343 m s^{- 1}$
Let $t_{1}$ be the time taken by the pebble to hit the bottom.
From second equation of motion,
$s = u t_{1} + \frac{1}{2} a t_{1}^{2}$
$100 = (0 \times t_{1}) + (\frac{1}{2} \times (10) \times t_{1}^{2})$
$100 = 5 t_{1}^{2}$
$\Rightarrow t_{1} = \sqrt{20} s$
We know, $t i m e = \frac{d i s t a n c e}{s p e e d}$
Let $t_{2}$ be the time taken for the sound wave to reach from the bottom to the top of the well.
$t_{2} = \frac{s}{v} = \frac{100}{343} \approx 0.3 s$
Total time,
$t = t_{1} + t_{2}$
$= \sqrt{20} + 0.3 s$ .

Question 35.

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 36.

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.

Question 37.

In human ear, the vibrations are amplified by:

Hammer
Anvil
Pinna
Stirrup

Discuss Question

Answer: Option B. -> Anvil
:
A, B, and D
In a human ear, the vibrations are amplified several times by three bones. They are called hammer, anvil, and stirrup.
The figure below shows the structure of human ear with hammer, anvil and stirrup.

In Human Ear, The Vibrations Are Amplified By:

Question 38.

Which of the following is true about the speed of sound?

It decreases with increase in temperature.
It is more in solid state as compared to the gaseous state.
It is the same in liquid and gaseous state.
It is the same in solid and gaseous state.

Discuss Question

Answer: Option B. -> It is more in solid state as compared to the gaseous state.
:
B
Sound wave travels fastest in solids, faster in liquids and slower in gases.
Temperature is the average kinetic energy of all the particles of a body. When the temperature increases for a given state of matter, the movement of particles increases and so does the speed of sound.

Question 39.

The part of the ear that vibrates in response to sound waves is:

Pinna
Cochlea
Eustachian tube
Eardrum

Discuss Question

Answer: Option D. -> Eardrum
:
D

Ear drum is the part of the ear that vibrates in response to the sound waves. The eardrum is a thin flap of skin that is stretched tight like a drum and vibrates when sound hits it. These vibrations move the tiny bones of the middle ear which send vibrations to the inner ear.

Question 40.

A person claps his hands in an empty room. He heard the echo of the sound after 5 seconds. What is the distance between the source of the sound and the reflecting surface, if the speed of sound in air is given as $340 m s^{- 1}$ ?