Doppler effect

The apparent change in frequency

The apparent change in frequency of sound due to relative motion between the source and the observer is called Doppler effect. Sound waves need a medi

For a stationary source

For a stationary source, wavelength is λ = v/n, where v is the velocity of sound and n is the true frequency.

When the source moves towards

When the source moves towards a stationary observer, wavelength shortens to λ' = (v - v_s)/n and apparent frequency becomes n' = n(v/(v-v_s)). When th

When the observer moves towards

When the observer moves towards a stationary source, apparent frequency is n' = n((v+v_o)/v). When the observer moves away, n' = n((v-v_o)/v).

If both move in the direction

If both move in the direction of sound, the apparent frequency is n' = n((v-v_o)/(v-v_s)). If the motion is opposite to the direction of sound, the si