The third overtone of a closed pipe is observed to be in unison with the second overtone of an open pipe. The ratio of the lengths of the pipes is-

1.  3/2

2.  5/3

3.  7/4

4.  7/6

Concept Questions :-

Standing waves
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A tuning fork and sonometer give 5 beats per second, when the length of the wire is 1 m and 1.05 m respectively. The frequency of fork is -

1. 210 Hz

2. 205 Hz

3. 410 Hz

4. 420 Hz

Concept Questions :-

Beats
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A person speaking normally produces a sound of intensity 40 dB at a distance of 1 m. If threshold intensity fo r reasonable audibility is 20 dB, the maximum distance at which he can be heared clearly is:

(1) 4 m

(2) 5 m

(3) 10 m

(4) 20 m

Concept Questions :-

Wave motion
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The equation of plane progressive wave motion is y=a sin 2$\mathrm{\pi }/\mathrm{\lambda }$(vt-x). Velocity of particle is

(1) $y\frac{dv}{dx}$

(2) $v\frac{dy}{dx}$

(3) $-y\frac{dv}{dx}$

(4) $-v\frac{dy}{dx}$

Concept Questions :-

Speed of sound
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The extension in a string, obeying Hook's law, is x. The speed of sound in the stretched string is v. If the extension in the string is increased to 1.5x, the speed of sound will be-

1.  1.22 v

2.  0.61 v

3.  1.50 v

4.  0.75 v

Concept Questions :-

Speed of sound
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If a sound source of frequency n approaches an observer with velocity v/4 and the observer approaches the source with velocity v/5, then the apparent frequency heard will be-

1.  (5/8)n

2.  (8/5)n

3.  (7/5)n

4.  (5/7)n

Concept Questions :-

Doppler effect
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When a sound wave travels from one medium to another, the quantity that remains unchanged is :

1.  speed

2.  amplitude

3.  frequency

4.  wavelength

Concept Questions :-

Wave motion
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In the phenomenon of interference of sound by two coherent sources if difference of intensity at maxima to intensity at minima is 20dB, then the ratio of intensities of the two sources is

1.  $\frac{121}{81}$

2.  $\frac{11}{9}$

3.  $\frac{101}{99}$

4.  $\frac{10}{1}$

Concept Questions :-

Wave motion
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The sound intensity level at a point 10 m away from a point source is 20dB, then the sound level at a distance 1m from the same source would be

(1) 40 dB

(2) 30 dB

(3) 200 dB

(4) 100 dB

Concept Questions :-

Wave motion
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Consecutive frequencies emitted from an organ pipe are 75Hz, 125Hz, 175Hz, the frequency of the 10th overtone will be

1.  275 Hz

2.  175 Hz

3.  525 Hz

4.  575 Hz

Concept Questions :-

Standing waves