A sound source S is moving along a straight track with speed ‘v’, and is emitting sound of frequency $v_{0}$ (see fig.) An observer is standing at a finite distance, at the point ‘O’, from the track. The time variation of frequency heard by the observer is best represented by :
( $t_{0}$ represents the instant when the distance between the source and observer is minimum)

Question

A sound source S is moving along a straight track with speed ‘v’, and is emitting sound of frequency $v_{0}$ (see fig.) An observer is standing at a finite distance, at the point ‘O’, from the track. The time variation of frequency heard by the observer is best represented by :

( $t_{0}$ represents the instant when the distance between the source and observer is minimum)

Infinity Learn · Accepted Answer

Apparent $$frequency=f$$'$$=$$ν$$0vsvs$$−vcosθ​∴f' depends inversely on θ.As the source, comes near until time $$t0$$ , θ increases and f' decreases.​At $$t=$$ $$t0$$, f' $$=$$ $$f0$$ , After t >$$t0$$  , f' $$=$$ ν$$0vsvs+vcos$$ϕ​∴As ϕ decreases, f' also decreases.

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