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Waves Calculations Involving the Doppler Effect Velocity of sound relative to air = v Frequency of emitted sound = f Apparent frequency of received sound = f’. Moving Source (stationary observer) If the source moves with a velocity of magnitude v_{s} (relative to the air) then the velocity of the waves relative to the source is (v±v_{s}). In general,
so in this case,
The apparent frequency of the sound, f’, as measured by the observer, will be equal to v/. Therefore, the apparent frequency is given by

