When a wave is reflected from a denser medium the change in phase is :

1.  0

2.  $\mathrm{\pi }$

3.  $2\mathrm{\pi }$

4.  $3\mathrm{\pi }$

In a stationary wave along a string, the strain is:
1. zero at the antinodes
2. maximum at the antinodes
3. zero at the nodes
4. maximum at the nodes

A source of sound moves away with the velocity of sound from a stationary observer. The frequency of the sound heard by the observer:

1. remains the same

2. is doubled

3. is halved

4. becomes infinity
 

The longitudinal waves can travel :

1.  only in liquids

2.  only in solids

3.  only in gases

4.  In liquids, solids, and gases

The equation of a wave pulse travelling along x-axis is given by $y=\frac{30}{2+{\left(x-20t\right)}^2}$, x and y are in meters and t is in seconds. The amplitude of the wave pulse is 

1.  5 m

2.  20 m

3.  15 m

4.  30 m

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

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.  $\frac{10}{1}$