A source of sonic oscillations with frequency `n=1700Hz` and a receiver are located on the same normal to a wall. Both the source and receiver are stationary, and the wall recedes from the source with velocity `u=6.0(m)/(s)`. Find the beat frequency registered by the receiver. The velocity of sound is `v=340(m)/(s)`.

Explanation

As both source and receiver are at rest the frequency of sound waves which directlyreach to receiver,will be 1700Hz and the frequency ofsound which wall will receive asa moving observer is
`n_(1) = n_(0) [(v)/(v + u)]`
The wall now behaves as a moving source of frequency `n_(1)` which when received by receiver, the frequency observed is
`n_(2) = n_(1) [(v -u)/(v)]`
` = n_(0) ((v - u)/(v + u))`
` = 1700 [(340 - 0.06)/(340 + 0.06)]`
` = 1700 xx (340 - 0.06)/(340 + 0.06)`
= 1699.4 Hz
Thus beat frequency received by detector is
`Deltan = 1700 - 1699.4 = 0.6 Hz`