Question

A sound source emits two sinusoidal sound waves, both of wavelength X, 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 exactly out of phase with the sound that travelled along path A. The minimum value of d in terms of λis :

• A. $\frac{\lambda}{8}$
• B. $\frac{\lambda}{4}$
• C. $\frac{3\lambda}{8}$
• D. $\frac{\lambda}{2}$

Answer 1

Answer: (A)

$\frac{\lambda}{8}$

Answer 2

Path difference = Path B - Path A = 7d-3d =4d For being out of phase

∆ x = 4d = $\frac{\lambda}{2};\frac{3\lambda}{2}$;................

For minimum d, 4d = $\frac{\lambda}{2}$

⇒ d = $\frac{\lambda}{8}$