# CBSE Class 9th Science 12 – Sound MCQs

#### The characteristic of a sound, which distinguishes a feeble sound from a loud sound of the same frequency is called ____.

Correct! Wrong!

The characteristic of a sound which distinguishes a feeble sound from a loud sound of the same frequency is called loudness.

#### Which of the following frequencies of sound waves are audible to human beings?

Correct! Wrong!

Frequency of 5,000 cycles/second is in the audible range of 20 Hz -20,000 Hz. Hence, only 5000 cycles/second frequency is audible to human beings.

#### A boy stands at a distance of 25 m from a cliff. He shoots a rifle and hears the echo at the end of 0.5 s. The velocity of sound in air is ____ m/s.

Correct! Wrong!

The distance travelled by the sound, s = 2 × 25 = 50 m Time taken to hear the echo, t = 0.5 s Velocity of sound, v = s /t v = 50 /0.5 v = 100 m/s The velocity of sound in air is 100 m/s.

#### A child hears an echo from a cliff 4 seconds after the sound is produced from a cracker. The distance of the cliff from the child is ____ m.

Correct! Wrong!

Consider the distance of the cliff from the child as'd' Distance = speed of sound × time ⇒ 2d = 344 × 4 ⇒ d = 688 m Hence, the distance of the cliff from the child is 688 m.

#### The distance between two consecutive crests or troughs is defined as ____.

Correct! Wrong!

The distance between two consecutive crests or troughs is defined as wave length.

#### Ultrasonic waves are those waves which a human being can hear.

Correct! Wrong!

Ultrasonic waves are sound waves with a frequency greater than 20 kHz, which is not audible to human being.

#### The voice of ladies is shrill because of ____.

Correct! Wrong!

That property of voice which we call pitch is determined by the rate of vibration of the vocal cords. The greater the number of vibrations per second, the higher the pitch. The rate of vibration, in turn, is determined by the length and thickness of the vocal cords and by the tightening or relaxation of these cords. Normally, women's voices are pitched higher than men's because women's vocal cords are shorter.

#### The maximum displacement suffered by the particles of a medium about their mean position is called ____.

Correct! Wrong!

The maximum displacement suffered by the particles of the medium about their mean position is called amplitude.

#### An echo is heard in 0.4 s, if the speed of sound is 330 m/s, then the distance of the reflecting surface is ____ m.

Correct! Wrong!

Given, t = 0.4 s, v = 330 m/s, s = ? As, 2s =v × t s = 330 × 0.4/2 s = 66 m Therefore, the distance of the reflecting surface is 66 m.

#### SONAR is based on the principle of resonance.

Correct! Wrong!

Sonar (which started as an acronym for sound navigation and ranging) is a technique that uses sound propagation (usually underwater) to navigate, communicate or to detect other vessels. SONAR is based on the principle of echo.

#### Human ear can hear a sound of wavelength ____ m.

Correct! Wrong!

v = nλ The audible range for human ear varies from 20 Hz to 20 kHz. λmin = v/nmax λmin = 340/20000 λmin = 0.017 m λmax= v/nmin λmax = 340/20 λmax = 17 m Hence, the audible range of wave lengths is 0.017 m to 17 m. Human ear can hear a sound of wavelength, 17 m.

#### A car blowing its horn at 480 Hz moves towards a high wall at a speed of 20 m/s. If the speed of sound is 340 m/s, the frequency of the reflected sound is ____ Hz.

Correct! Wrong!

During reflection, the frequency of sound does not change. Hence, frequency of the reflected sound, n = 480 Hz.

#### Longitudinal waves can travel in ____.

Correct! Wrong!

Longitudinal wave can travel in solids, liquids and gases.

#### The average amount of energy passing through a unit area per unit time in a specified direction is called ____ of the wave.

Correct! Wrong!

Intensity of the wave is defined as the average amount of energy passing through a unit area per unit time in a specified direction.

#### An echo is a phenomenon of reflection of sound from an obstacle.

Correct! Wrong!

An echo is a phenomenon of reflection of sound from an obstacle.

#### A boy shouts into a deep well and hears the echo at the end of 0.4s. If the speed of sound in air is 350 m/s, then, the depth of the water level in the well is ____ m.

Correct! Wrong!

Time taken by the sound to go from the top of the well to the water level in the well and back to the top of the well = 0.4 s t=0.4/2⁡ t = 0.2 s But, s = vt, where 'v' is the velocity of the sound in air and 't' is the time taken by the sound to travel from the top of the well to the water level Hence, s = 350 × 0.2 s = 70 m Therefore, the depth of the water level in the well is 70 m.

#### When the particles of the medium vibrate perpendicular to the propagation of the wave, then the wave is called ____ wave.

Correct! Wrong!

In transverse wave, particles of the medium vibrate perpendicular to the propagation of the wave.

#### A boy standing between two cliffs claps and hears 2 echoes at the end of 1 s and 1.5 s respectively. If the velocity of sound in air is 350 m/s, then the distance between the two cliffs is ____ m.

Correct! Wrong!

Velocity of sound, v= 2d/t d= v x t/2 Distance between the boy and the first cliff, d1 = 350 × ½ Distance between the boy and the first cliff, d1= 175 m Distance between the boy and the second cliff, d2=350 × 1.5/2 Distance between the boy and the second cliff, d2 = 262.5 m Hence, the total distance between the two cliffs, d = d1+d2 d = 175 + 262.5 d = 437.5 m Therefore, the distance between the two cliffs is 437.5 m.

#### The speed of sound at 0 °C is 330 m/s. Then, the speed of sound at a temperature of 20 °C is ____ m/s.

Correct! Wrong!

For 1 °C rise in temperature, the increase in speed is 0.6 m/s For 20 °C rise in temperature, the increase in speed is 0.6 × 20 = 12 m/s Speed of sound at 20 °C is 330 + 12 Speed of sound at 20 °C is 342 m/s.

#### An electric vibrator produces ripples in a ripple tank, such that the distance between one crest and one trough is 2 cm. If the vibrations are produced at a rate of 4800 per minute. Then, the time period is ____ s.

Correct! Wrong!

Distance between one crest and one trough= λ/2 = 2 cm or, λ=4 cm Frequency of the vibrator, v= 4800 min-1 U=4800/60 U= 80 H As, n= v/ λ T=1/n T=1/80 T= 0.0125 s Therefore, the time period of the wave is 0.0125 s

#### Among the following properties of a wave, the one that is independent of the other is its ____.

Correct! Wrong!

The maximum displacement of the particle from its mean position is defined as amplitude where the wave is independent of it.

#### The wave length of a tuning fork of frequency 380 Hz, which is set to vibrate considering the velocity of sound in air is 332 m/s is ____ m.

Correct! Wrong!

v = nλ 332 = 380 × λ λ = 332/380 λ = 0.8736 m Therefore, the wavelength of the wave is 0.8736 m.

#### The time taken by a particle of a medium to complete one vibration is called ____.

Correct! Wrong!

Time taken by a particle of medium to complete one vibration is called time period.

#### Echo is produced due to the resonance of sound.

Correct! Wrong!

Echo is produced due to reflection of sound.

#### The wave in which the individual particles of a medium oscillate along the direction of wave propagation is called ____.

Correct! Wrong!

The wave in which the individual particles of the medium oscillate along the direction of wave propagation is called longitudinal wave.

#### The velocity of sound in air is not affected by change in ____.

Correct! Wrong!

Atmospheric pressure does not affect the velocity of sound.

#### The persistence of hearing for human beings is ____ s.

Correct! Wrong!

In human beings the persistence of hearing is 1/10s.

#### A sound wave propagating through a medium has bounced back into the same medium by hitting a hard surface and then such a phenomenon is called ____ of sound.

Correct! Wrong!

A sound wave propagating through a medium has bounced back into the same medium by hitting a hard surface and then such a phenomenon is called reflection of sound.

#### SONAR is the technique based on the principle of reflection of sound.

Correct! Wrong!

SONAR - sound navigation and ranging is the technique based on the principle of reflection of sound.

#### The kind of motion in which transfer of energy takes place when the particles move about their mean position is called ____ motion.

Correct! Wrong!

When a disturbance is created in an elastic medium, it is transferred from one particle to another particle in the form of a wave. This type of propagation is known as wave motion.

CBSE Class 9th Science 12 - Sound MCQs
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