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

1.  speed

2.  amplitude

3.  frequency

4.  wavelength

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

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) $-v\frac{dy}{dx}$

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

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

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.  $\frac{10}{1}$

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

Consecutive frequencies emitted from an organ pipe are 75Hz, 125Hz, 175Hz.  The frequency of the tenth overtone will be:

1.  275 Hz

2.  175 Hz

3.  525 Hz

4.  575 Hz

Eleven tuning forks are arranged in increasing order of frequency in such a way that any two consecutive tuning forks produce 4 beats per second. The highest frequency is twice that of the lowest. The highest and the lowest frequencies (in Hz) are, respectively:

1.  100 and 50

2.  44 and 22

3.  80 and 40

4.  72 and 30

The equation of a standing wave in a string is $\mathrm{y}=\left(200\mathrm{m}\right)\sin \frac{2\mathrm{\pi }}{50}\mathrm{xcos}\frac{2\mathrm{\pi }}{0.01}\mathrm{t}$ where x is in meters and t is in seconds. At the position of antinode, how many times does the distance of a string particle become 200 m from its mean position in one second?

1.  100 times

2.  50 times

3.  200 times

4.  400 times