A source of sound of frequency `256Hz` is moving rapidly towards wall with a velocity of `5m//sec`. How many beats per second will be heard if sound travels at a speed of `330m//sec`.

Options

A. 6
B. 8
C. 10
D. 4

Answer

B

Explanation

`v_(o) = 5m//s, v = 330 m//s, v_(s) = v_(o) = 5 m//s`
By Dopplyer's principle, the apparent frequency heard by the observer is
`:. n_(a) = ((v + v_(o))/(v - v_(s)))n = ((330 + 5)/(330 - 5)) xx 256`
`= ((335)/(325)) x 256 div 264 Hz`
`:.` No. of beats/s `= n_(a) - n = 264 - 256 = 8`