Question

Two coherent sound sources $A$ and $B$ produce a sound of wavelength $\lambda $ . If at $t=0$ a detector starts moving with constant velocity $v_{0}$ from point $O$ along y-direction, then the minimum time, after which it detects the sound of maximum intensity, is $\left(D \, > > \lambda \right)$

• A. $\frac{\sqrt{7} \, D}{v_{0}}$
• B. $\frac{D}{3 v_{0}}$
• C. $\frac{D}{v_{0}}$
• D. $\frac{\sqrt{7 \, \, } D}{3 v_{0}}$

Answer 1

Answer: (D)

$4\lambda \, cos \, \theta =3\lambda $
$cos \, \theta =\frac{3}{4}$
$\Rightarrow tan \, \theta =\frac{y}{D}$
$\Rightarrow y=\frac{\sqrt{7} D}{3}$
$t=\frac{\sqrt{7} D}{3 \, v_{0}}$