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%
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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%
From NCERT
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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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Intensity level of a sound of intensity I is 30 dB. The ratio II0 is (Where I0 is the threshold of hearing) 

(1) 3000

(2) 1000

(3) 300

(4) 30

Subtopic:  Pressure Wave in Sound |
 73%
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Quality of a musical note depends on :

(1) Harmonics present

(2) The amplitude of the wave

(3) Fundamental frequency

(4) The velocity of sound in the medium

Subtopic:  Standing Waves |
 52%
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If T is the reverberation time of an auditorium of volume V then :

(1) T1V

(2) T1V2

(3) TV2

(4) TV

Subtopic:  Pressure Wave in Sound |
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The intensity level due to two waves of the same frequency in a given medium are 1 bel and 5 bel. Then the ratio of amplitudes is :

(1) 1 : 4

(2) 1 : 2

(3) 1 : 104

(4) 1 : 102

Subtopic:  Pressure Wave in Sound |
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