Question

A source of sound of frequency 256 hertz is moving rapidly towards a wall, with a speed of 5 m/s. How many beats per second will be heard if sound travels at a speed of 330 m/s in the surrounding medium.

Answer 1

If the sound reaches the observer after being reflected from a stationary surface and the medium is also stationary, the image of the source in the reflecting surface will become the source of the reflected sound.

v = v [c – v0/c – vs]

v0, vs are +ve if they are directed from source to the observer and – ve if they directed from observer to source.

v = 256 [330 – (- 5)/330 – 5] = 264 Hz

∴ Beat frequency = 264 – 256 = 8

Thanks

Aditi Chauhan

askIITians Faculty