Doppler Effect

A change in the frequency of a periodic wave due to the motion of the observer, the source, or both.

It occurs both in sound as well as electromagnetic phenomena, although it takes on different forms in each.

Source toward stationary observer

Source away from stationary observer

Observer toward stationary source

Observer away from stationary source

where

c = wave velocity in fluid [ms^-1]

f = emitted frequency [Hz]

f' = observed frequency [Hz]

V_s = velocity of source [ms^-1]

V_o = velocity of observer [ms^-1]

See also: Blue Shift, Doppler Sonar, Frequency, Redshift.

Further reading:
• Advanced Physics for You, Keith Johnson, Simmone Hewett, Sue Holt, John Miller, Nelson Thornes