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) |
 62%
From NCERT
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NEET 2023 - Target Batch - Aryan Raj Singh
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Two whistles A and B produce notes of frequencies 660 Hz and 596 Hz respectively. There is a listener at the mid-point of the line joining them. Now the whistle B and the listener start moving with speed 30 m/s away from the whistle A. If the speed of sound be 330 m/s, how many beats will be heard by the listener :

(1) 2

(2) 4

(3) 6

(4) 8

Subtopic:  Beats |
 75%
From NCERT
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A source producing the sound of frequency 170 Hz is approaching a stationary observer with a velocity of 17 ms–1. The apparent change in the wavelength of sound heard by the observer is (speed of sound in air = 340 ms–1

1. 0.1m

2. 0.2m

3. 0.4m

4. 0.5m

Subtopic:  Doppler's Effect (OLD NCERT) |
 59%
From NCERT
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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 motorcyclist does not observe any beats.
(Speed of sound=330 m/s) 

(1) 33 m/s

(2) 22 m/s

(3) Zero

(4) 11 m/s

Subtopic:  Doppler's Effect (OLD NCERT) |
 63%
From NCERT
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An observer moves towards a stationary source of sound with a speed 1/5th of the speed of sound. The wavelength and frequency of the sound emitted are λ and f respectively. The apparent frequency and wavelength recorded by the observer are respectively :

1. 1.2f, λ

2. f,1.2λ

3. 0.8f,0.8λ

4. 1.2f,1.2λ

Subtopic:  Doppler's Effect (OLD NCERT) |
 71%
From NCERT
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Consider ten identical sources of sound all giving the same frequency but having phase angles which are random. If the average intensity of each source is I0, the average of resultant intensity I due to all these ten sources will be :

(1) I = 100 I0

(2) I = 10 I0

(3) I = I0

(4) I=10I0

Subtopic:  Energy of Waves |
 52%
From NCERT
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41 forks are so arranged that each produces 5 beats per sec when sounded with its near fork. If the frequency of the last fork is double the frequency of the first fork, then the frequencies of the first and last fork are respectively :

(1) 200, 400

(2) 205, 410

(3) 195, 390

(4) 100, 200

Subtopic:  Beats |
 70%
From NCERT
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16 tunning forks are arranged in the order of increasing frequencies. Any two successive forks give 8 beats per sec when sounded together. If the frequency of the last fork is twice the first, then the frequency of the first fork is 

(1) 120

(2) 160

(3) 180

(4) 220

Subtopic:  Standing Waves |
 78%
From NCERT
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The frequency of a stretched uniform wire under tension is in resonance with the fundamental frequency of a closed tube. If the tension in the wire is increased by 8 N, it is in resonance with the first overtone of the closed tube. The initial tension in the wire is 

(1) 1 N

(2) 4 N

(3) 8 N

(4) 16 N

Subtopic:  Standing Waves |
 65%
From NCERT
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A metal wire of linear mass density of 9.8 g/m is stretched with a tension of 10 kg weight between two rigid supports 1 metre apart. The wire passes at its middle point between the poles of a permanent magnet, and it vibrates in resonance when carrying an alternating current of frequency n. The frequency n of the alternating source is :

(1) 25 Hz

(2) 50 Hz

(3) 100 Hz

(4) 200 Hz

Subtopic:  Travelling Wave on String |
 70%
From NCERT
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