3.8 Doppler Effect

Have you ever heard an approaching train and noticed distinct change in the pitch of the sound of its whistle, when it passes away ?

Same thing similar happens when a listener moves towards or away from the stationary source of sound.

Such a phenomenon was first identified in 1842 by Austrian physicist Christian Doppler (1803-1853) and is known as Doppler effect.

When a source of sound and a listener are in motion relative to each other the frequency of sound heard by listener is not the same as the frequency emitted by the source.

Doppler effect is the apparent change in frequency of sound due to relative motion between the source and listener.

Doppler effect is a wave phenomenon.

It holds for sound waves and also for EM waves.

But here we shall consider it for sound waves only.

The changes is frequency can be studied under 3 different conditions:

1) When listener is stationary but source is moving.

2) When listener is moving but source is stationary.

3) When listener and source both are moving.