Question

# Explain Doppler effect in sound. State any two applications of Doppler effect.

Solution

## When there is a relative motion between a source and an observer there is the apparent change in frequency of a sound emitted by the source as heard by the observer. This phenomenon is called the Doppler effect.The formula for apparent frequency can be given as:-$$f'=\dfrac{(v\pm v_0)}{(v\pm v_s)}f$$Here, $$f$$ is actual frequency emitted by the source, $$f'$$  is observed/apparent frequency, $$v$$ velocity of sound in the medium.$$v_0$$ is the velocity of the observer, $$(+ve)$$ for an observer moving towards source, $$(-ve)$$ for observed moving away from sources.$$v_s$$ is the velocity of the source, $$(+ve)$$ for source moving away from observer $$(-ve)$$ for source moving towards the observer.Two applications of the Doppler effect are:-1) Used in sonography- Ultrasonic waves reflected from body tissues can give information about the rate of flow of various fluids including blood.2) Handheld radar guns used by police to check for speeding vechicles.Physics

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