Q. Two sound sources emitting sound each of wavelength $\lambda$ are fixed at a given distance apart. A listener moves with a velocity $u$ along the line joining the two sources. The number of beats heard by him per second is
A) $2u/\lambda$
B) $u/\lambda$
C) $\frac{u}{3\lambda}$
D) $\frac{2\lambda}{u}$
Explanation
(a) Number of extra waves received $s^{- 1} = \pm u/\lambda$
$\therefore$ Number of beats $s^{- 1} = \frac{u}{\lambda} - ( - u/\lambda) = \frac{2u}{\lambda}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.