A sound source emits two sinusoidal sound waves, both of wavelength `lambda`, along paths A and B as shown in figure.The sound travelling along path B is reflected from five surfaces as shown and then merges at point Q, producing minimum intensity at that point.The minimum value of d in terms of `lambda` is :

Options

A. `lambda/8`
B. `lambda/4`
C. `(3lambda)/8`
D. `lambda/2`

Explanation

Path difference = Path B-Path A =7d-3d=4d
[Note that there is no phase change in reflections from mirror in case of sound]
For being out of phase :
`Deltax=4d=lambda/2 , (3lambda)/2`,....
For minimum d, `4d=lambda/2`
`rArr d=lambda/8`