Question

What is doppler effect?

Answer 1

Doppler Effect:
The apparent frequency of sound heard by the observer due to the relative motion between the source and the observer is called Doppler Effect.
- The technique of Doppler effect is, mainly applied by sending a sound wave or an   electromagnetic wave towards a moving object and determining the apparent frequency of   the reflected wave.
Eg: The frequency of sound heard by a person when a train is approaching him.

Answer 2

Doppler effect :

Change in observed frequency of a wave, when the source S and observer O moves relative to the medium.

f= f0 ( v + - v0 / v + - vs )