when a source of sound of frequency f crosses stationary observer with a speed ` v_(s) (lt lt ` speed of sound v) , the apparent change in frequency ` Deltaf` is given by

Options

A. `(2fv_(s))/(v)`
B. `2fv v_(s)`
C. `(2fv)/(v_(s))`
D. `(fv_(s))/(v)`

Answer

A

Explanation

`Deltaf = f_(1)-f_(2)`

`=f((v)/(v-v_(s)))-f((v)/(v+v_(s)))`
`= f[(1-(v_(s))/(v))^(-1) - (1+(v_(s))/(v))^(-1)]`
`=f[(1+(v_(s))/(v))-(1-(v_(s))/(v))]=(2fv_(s))/(v)`