CBSE Class 9 Science Sound MCQs Set C

Question. Which of the following is an elastic wave?
(a) Sound waves
(b) Light waves
(c) X -rays
(d) Radio waves

Answer: a

Question. In case of transverse waves the particles of a medium vibrate
(a) in the direction of wave propagation
(b) opposite to the direction of wave propagation
(c) at the right angles to the direction of wave propagation
(d) none of the above

Answer: c

Question. When a sound wave travels in air, the physical quantity which is transferred from one place to the other is
(a) mass
(b) force
(c) air particle
(d) energy

Answer: d

Question. A sonar signal from a ship is emitted underwater towards the sea bed. It takes 0.7 s for the signal to bounce back from the sea bed. If sound travels at 1500 m s-1 in water, how deep is the sea?
(a) 525 m
(b) 1050 m
(c) 1071 m
(d) 2143 m

Answer: a

Question. The eardrum is a
(a) bone
(b) fluid
(c) coiled tube
(d) a stretched membrane

Answer: d

Question. In case of transverse waves, the particles of a medium vibrate
(a) in the direction of wave propagation
(b) opposite to the direction of wave propagation
(c) at the right angles to the direction of wave propagation
(d) none of these

Answer: c

Question. Which is not the condition for hearing sound?
(a) There must be a vibrating body capable of transferring energy.
(b) there must be a material medium to pick up and propagate energy.
(c) The medium must have a large density.
(d) There must be receiver to receive the energy and interpret it.

Answer: c

Question. Which of the following statements are correct?
(a) Sound is a form of energy which produces a sensation of hearing in our ears.
(b) Sound cannot be produced without utilizing energy.
(c) Vibrating objects produce sound.
(d) All of these

Answer: d

Question. The change in density/pressure of a medium from maximum value to minimum value and again to maximum value, due to the propagation of a longitudinal wave is called a complete
(a) oscillation
(b) frequency
(c) amplitude
(d) none of these

Answer: a

Question. Non-mechanical wave can travel
(a) in vacuum as well as in a medium
(b) in vacuum but not in a medium
(c) in medium but not in vacuum
(d) neither in a medium nor in vacuum

Answer: a

Question. Sound is produced by ………. the objects.
(a) plucking
(b) scratching
(c) blowing
(d) all of these

Answer: d

Question. Sound travels at a speed of 334 m s-1 in air. This means that
(a) the source of sound moves 334 m in one second
(b) the listener moves 334 m in one second
(c) air moves 334 m in one second
(d) the disturbance in air moves 334 m in one second

Answer: d

Question. Which of the following changes when sound is reflected?
(a) Wavelength
(b) Frequency
(c) Speed
(d) Amplitude

Answer: d

Question. If the density of air at a point through which a sound wave is passing is maximum at an instant, the pressure at that point will be
(a) minimum
(b) same as the density of air
(c) equal to the atmospheric pressure
(d) maximum

Answer: d

Question. In the region of compression or rarefaction, in a longitudinal wave the physical quantity which does not change is
(a) pressure
(b) mass
(c) density
(d) volume

Answer: c

Question. Sound waves and light waves are similar in that both ………. .
(a) are produced by mechanical vibrations
(b) are longitudinal waves
(c) can travel through vacuum
(d) obey the laws of reflection

Answer: d

Question. A bat releases a sound wave forward. It detects an echo 0.8 s later. If the speed of sound in air is 300 m s-1 , how far is the bat away from the obstacle in front?
(a) 120 m
(b) 240 m
(c) 300 m
(d) 375 m

Answer: a

Question. Human ear cannot hear those mechanical waves whose frequency lies in the frequency range
(a) less than 100 Hz but greater than 10000 Hz
(b) between 1000 Hz and 5000 Hz
(c) between 500 Hz and 20000 Hz
(d) less than 20 Hz and more than 20000 Hz

Answer: d

Question. In inner ear, the pressure variations are turned into electrical signals by
(a) Oval window
(b) Cochlea
(c) Auditory canal
(d) Eardrum

Answer: b

FILL IN THE BLANK

Question. Loudness of a note increases with the increase in _____
Answer: amplitude

Question. The frequency of the particles oscillating in a medium is _____ the frequency of waves in the medium.
Answer: the same as

Question. Wave motion involves the transport of _____
Answer: Energy

Question. The functions which can be represented by a sine or a cosine function are called _____ functions.
Answer: harmonic.

Question. The total energy E of sound is related to their frequency as _____
Answer: E ∝ v2

Question. A longitudinal wave is made up of _____
Answer: compression and rarefactions

Question. Velocity = frequency × _____
Answer: Wavelength

TRUE/FALSE

Question. The rate of transfer of energy in a wave depends directly on the square of the wave amplitude and square of the wave frequency.
Answer: True

Question. Velocity of sound in air at the given temperature decreases with increases in pressure.
Answer: False

Question. Bells are made of metal and not of wood because the sound is not conducted by metals but is radiated.
Answer: False

Question. High pitch of sound has a high frequency.
Answer: True

Question. Velocity of sound in air at the given temperature decreases with increase in pressure.
Answer: False

Question. The total energy of a simple harmonic oscillator is constant.
Answer: True

ASSERTION AND REASON

Question. Assertion : The speed of sound in solids is maximum though their density is large.
Reason : The coefficient of elasticity of solid is large.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : Transverse waves travel through air in an organ pipe.
Reason : Air possesses only volume elasticity.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: d

Question. Assertion : The velocity of sound in hydrogen gas is less than the velocity of sound in oxygen gas.
Reason : The density of oxygen is more than the density of hydrogen.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: d

Question. Assertion : Sound would travel faster on a hot summer day than on a cold winter day.
Reason : Velocity of sound is directly proportional to the square of its absolute temperature.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: c

Question. Assertion : Sound would travel faster on a hot summer day than on a cold winter day.
Reason : Velocity of sound is directly proportional to the square of its absolute temperature.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: c

Question. Assertion : A vibrating tuning fork sounds louder when its stem is pressed against a desktop.
Reason : When a wave reaches another denser medium, part of the wave is reflected.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: c

Question. Assertion : Compression and rarefaction involve changes in density and pressure.
Reason : When particles are compressed, density of medium increases and when they are rarefied, density of medium decreases.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: a

Question. Assertion : The velocity of sound changes as we go up in the atmosphere.
Reason : Pressure decreases as we go up in the atmosphere.
Options:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Answer: b