NEET Physics Musical Sound and Dopplers Effect MCQs Set A

a) intensity and frequency

b) frequency and number of harmonics

c) frequency and velocity

d) intensity and velocity

Answer: intensity and frequency

Question:  A source of sound is moving with a uniform speed along a circle. The frequency of sound as heard by listener stationed at the centre of the path

a) decreases

b) increases

c) may increase and decrease alternately

d) remains the same

Answer: decreases

Question: Doppler's effect in sound takes place when source and observer are

a) in relative motion

b) moving with same velocity

c) stationary

d) None of these

Answer: in relative motion

Question: Doppler phenomena is related with

a) Pitch (Frequency)

b) Quality

c) Loudness

d) Reflection

Answer: Pitch (Frequency)

Question: Doppler shift in frequency does not depend upon

a) distance from the source to the listener

b) frequency of the wave produced

c) velocity of the observer

d) velocity of the source

Answer:  distance from the source to the listener

Question: For which of the following cases, there will be no Doppler effect?

a) All of these

b) When both the source and listener are at rest.

c) If one of the source/listener is at the centre of a circle, while the other is moving on it

d) If source and listener, both move in the same direction with same speed.

Answer: All of these

Question:  Choose the false statement(s) from the following.
I. Change in frequency due to Doppler effect will be positive if the distance between source and listenerincreases.
II. Change in frequency due to Doppler effect will be negative if the distance between source and listener

a) I and II

b) I only

c) II only

d) None of these

Answer: I and II

More Questions.....................................

Question: Assertion : Doppler formula for sound wave is symmetric with respect to the speed of source and speed of observer.
Reason : Motion of source with respect to stationary observer is not equivalent to the motion of an observer with respect to stationary source.

a) Assertion is incorrect, reason is correct

b) Assertion is correct, reason is incorrect

c) Assertion is correct, reason is correct; reason is not a correct explanation for assertion

d) Assertion is correct, reason is correct; reason is a correct explanation for assertion.

Answer: Assertion is incorrect, reason is correct

Question: The musical interval between two tones of frequencies 320 Hz and 240 Hz is:

a) 320 X 240

b) 560

c) (4/3)

d) 80

Answer: 320 X 240

Question: A is singing a note and at the same time B is singing a note with exactly one-eight the frequency of the note of A. The energies of the two sounds are equal. The amplitude of the note of B is:

a) twice that of A

b) eight times that of A

c) four times that of A

d) same as that of A

Answer: twice that of A

Question:  A whistle of frequency 385 Hz rotates in a horizontal circle of radius 50 cm at an angular speed of 20 radians s^–1. The lowest frequency heard by a listener a long distance away at rest with respect to the centre of the circle, given velocity of sound equal to 340 ms^–1, is

a) 374 Hz

b) 385 Hz

c) 363 Hz

d) 396 Hz

Answer: 374 Hz

Question: The power of a sound from the speaker of a radio is 20 milliwatt. By turning the knob of the volume control the power of sound is increased to 400 milliwatt. The power increases (indecibel) as compared to the original power is:

a) 13

b) 10

c) 20

d) 800

Answer: 13

Question:  A sound source emits frequency of 180 Hz when moving towards a rigid wall with speed 5 m/s and an observer is moving away from wall with speed 5 m/s. Both source and observer moves on a straight line which is perpendicular to the wall. The number of beats per second heard by the observer will be [Speed of sound = 355 m/s]

a) 5 beats/s

b) 6 beats/s

c) 10 beats/s

d) 8 beats/s

Answer: 5 beats/s

Question: Two trains are moving towards each other with speeds of 20m/s and 15 m/s relative to the ground. The first train sounds a whistle of frequency 600 Hz. The frequency of the whistle heard by a passenger in the second train before the train meets, is (the speed of sound in air is 340 m/s)

a) 666 Hz

b) 645 Hz

c) 585 Hz

d) 600 Hz

Answer: 666 Hz

Question: Two trains move towards each other with the same speed. The speed of sound is 340 m/s. If the height of the tone of the whistle of one of them heard on the other changes 9/8 times, then the speed of each train should be

a) 20 m/s

b) 2 m/s

c) 200 m/s

d) 2000 m/s

Answer:  20 m/s

Question: A source producing sound of frequency 170 Hz is approaching a stationary observer with a velocity 17 ms^–1. The apparent change in the wavelength of sound heard by the observer is (speed of sound in air = 340 ms^–1)

a) 0.1 m

b) 0.2 m

c) 0.4 m

d) 0.5 m

Answer: 0.1 m

Question: A train approaching a hill at a speed of 60 km/hour sounds a whistle of frequency 600 Hz when it is at a distance of 1 km from the hill. Wind is blowing in the direction of the train with a speed of 60 km/h. Find the frequency of the whistle heard by an observer on the hill: (Velocity of sound in air = 1200 km/h)

a) 630 Hz

b) 650 Hz

c) 620 Hz

d) 610 Hz

Answer: 630 Hz

Question: A man is watching two trains, one leaving and the other coming in with equal speeds of 4m/sec. If they sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air = 320 m/sec) will be equal to

a) 6

b) 3

c) 0

d) 12

Answer:  6