If source and observer both are relatively at rest and if speed of sound is increased then frequency heard by observer will :

(1) Increases

(2) Decreases

(3) Can not be predicted

(4) Will not change

Subtopic:  Doppler's Effect (OLD NCERT) |
 78%
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A source and an observer move away from each other with a velocity of 10 m/s with respect to ground. If the observer finds the frequency of sound coming from the source as 1950 Hz, then actual frequency of the source is (velocity of sound in air = 340 m/s) 

(1) 1950 Hz

(2) 2068 Hz

(3) 2132 Hz

(4) 2486 Hz

Subtopic:  Doppler's Effect (OLD NCERT) |
 78%
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A whistle revolves in a circle with an angular speed of 20 rad/sec using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer, which is far away from the centre in the same plane ? (vsound = 340 m/s)

(1) 333 Hz

(2) 374 Hz

(3) 385 Hz

(4) 394 Hz

Subtopic:  Doppler's Effect (OLD NCERT) |
 66%
From NCERT
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A Siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s, frequency of the sound to be heard by the listener is (take velocity of sound as 330 m/s)

(1) 733.3 Hz

(2) 644.8 Hz

(3) 481.2 Hz

(4) 286.5 Hz

Subtopic:  Doppler's Effect (OLD NCERT) |
 87%
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A source emits a sound of frequency of 400 Hz, but the listener hears it to be 390 Hz. Then 

(1) The listener is moving towards the source

(2) The source is moving towards the listener

(3) The listener is moving away from the source

(4) The listener has a defective ear

Subtopic:  Doppler's Effect (OLD NCERT) |
 89%
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Two waves having sinusoidal waveforms have different wavelengths and different amplitudes. They will be having :

(1) Same pitch and different intensity

(2) Same quality and different intensity

(3) Different quality and different intensity

(4) Same quality and different pitch

Subtopic:  Pressure Wave in Sound |
 67%
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The ends of a stretched wire of length L are fixed at x = 0 and x = L. In one experiment, the displacement of the wire is y1=Asin(πx/L)sinωt and energy is E1, and in another experiment its displacement is y2=Asin(2πx/L)sin2ωt and energy is E2. Then :

(1) E2 = E1

(2) E2 = 2E1

(3) E2 = 4E1

(4) E2 = 16E1

Subtopic:  Energy of Waves |
 59%
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The difference between the apparent frequency of a source of sound as perceived by an observer during its approach and recession is 2% of the natural frequency of the source. If the velocity of sound in air is 300 m/sec, the velocity of the source is : (It is given that velocity of source << velocity of sound) 

(1) 6 m/sec

(2) 3 m/sec

(3) 1.5 m/sec

(4) 12 m/sec

Subtopic:  Doppler's Effect (OLD NCERT) |
 61%
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A police car moving at 22 m/s, chases a motorcyclist. The policeman sounds his horn at 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of the motorcycle, if it is given that he does not observe any beats 

(1) 33 m/s

(2) 22 m/s

(3) Zero

(4) 11 m/s

Subtopic:  Beats |
 61%
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The equation of displacement of two waves are given as y1=10sin3πt+π3; y2=5(sin3πt+3cos3πt). Then what is the ratio of their amplitudes ?

1. 1 : 2

2. 2 : 1

3. 1 : 1

4. None of these

Subtopic:  Wave Motion |
 66%
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