When a source of sound of frequency f crosses a stationary observer with a speed $v_{s}$ (≪ speed of sound v), the apparent change in frequency $Δ$ f is given by

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The source producing sound and an observer both are moving along the direction of proppagation of sound waves. If the respective velocites of sound, source and observer are v,vs and v0, then the apparent frequency heard by the observer will be (n= frequency of sound)

The correct option is A n(v−vo)v−vsAs both observer and source are moving in the direction of sound, so the velocities are as per sing convention are positive.So, the apparent frequency is given asn′=n(v−v0)(v−vs)

The source producing sound and an observer both are moving along the direction of proppagation of sound waves. If the respective velocites of sound, source and observer are $v, v_{s}$ and $v_{0}$ , then the apparent frequency heard by the observer will be ( $n =$ frequency of sound)

The correct option is A $\frac{n (v - v_{o})}{v - v_{s}}$
As both observer and source are moving in the direction of sound, so the velocities are as per sing convention are positive.
So, the apparent frequency is given as
$n^{'} = n \frac{(v - v_{0})}{(v - v_{s})}$