# ICSE Class 9th Physics 7 – Sound MCQs

#### A source produces 60 crests and 60 troughs in 0.6 second. Then, the time period of the wave is ____ s.

Correct! Wrong!

source produces 60 full wave cycles in 0.6second. Number of wave cycles produced in 1 s is frequency, n N = 60/0.6 N = 100S-1 Time period, T = 1/n T = 1/100 T = 0.01S

#### 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.

#### 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.

#### 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.

#### 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 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.

#### 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.

#### 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 = 12m/s Speed of sound at 20 °C is 330 + 12 Speed of sound at 20 °C is 342 m/s.

#### 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.

#### 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.

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

Correct! Wrong!

Atmospheric pressure does not affect the velocity of sound.

#### 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.

#### 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.

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

Correct! Wrong!

Echo is produced due to 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 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.

#### 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.

#### 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.

#### 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.

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

Correct! Wrong!

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

#### Longitudinal waves can travel in ____.

Correct! Wrong!

Longitudinal wave can travel in solids, liquids and gases.

#### 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.

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 ____ 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.

ICSE Class 9th Physics 7 - Sound MCQs
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