JEE Main · PhysicsHard

$Two identical sound sources emit waves of frequency f . An observer moves along the line joining them with a constant velocity v . What is the beat frequency heard by the observer?$

Show correct answer & step-by-step solution

Correct answer: A — $$2fv / c$$

Solution

The observer hears a Doppler-shifted frequency f_{1} = f (c + v) / c from one source and f_{2} = f (c - v) / c from the other. The beat frequency is ∣ f_{1} - f_{2} ∣ = ∣ f (c + v) / c - f (c - v) / c ∣ = 2 f v / c .