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) |
 76%
From NCERT
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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) |
 74%
From NCERT
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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) |
 72%
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) |
 82%
From NCERT
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A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before and after the passing of the car is 11 : 9. If the speed of sound is v, the speed of the car is 

(1) 110v

(2) 12v

(3) 15v

(4) v

Subtopic:  Doppler's Effect (OLD NCERT) |
 80%
From NCERT
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A small source of sound moves on a circle as shown in the figure and an observer is standing on O. Let n1, n2 and n3 be the frequencies heard when the source is at A, B, and C respectively. Then

(1) n1 > n2 > n3

(2) n2 > n3 > n1

(3) n1 = n2 > n3

(4) n2 > n1 > n3

Subtopic:  Doppler's Effect (OLD NCERT) |
 62%
From NCERT
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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) |
 84%
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A person carrying a whistle emitting continuously a note of \(272~\text{Hz}\) is running towards a reflecting surface with a speed of \(18~\text{km/hr}\). The speed of sound in air is \(345~\text{m/s}\). The number of beats heard by him is: 
1. \(4\)
2. \(6\)
3. \(8\)
4. \(3\)

Subtopic:  Beats |
 59%
From NCERT
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If the pressure amplitude in a sound wave is tripled, then the intensity of sound is increased by a factor of

(1) 9

(2) 3

(3) 6

(4) 3

Subtopic:  Energy of Waves |
 71%
From NCERT
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If the amplitude of the sound is doubled and the frequency reduced to one-fourth, the intensity of sound at the same point will be :

(1) Increased by a factor of 2

(2) Decreased by a factor of 2

(3) Decreased by a factor of 4

(4) Unchanged

Subtopic:  Pressure Wave in Sound |
 68%
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