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Doppler Effect

• If either the observer and/or the sound source are moving, the frequency heard by the observer differs from that when both are stationary; this is the Doppler Effect.
• If the observer and source are stationary, f = v/λ, where v is the speed of sound.
• Case 1: Observer moves with velocity u toward a stationary source: f’=f (1 + u/v).
• Case 2: Observer moving with velocity u away a stationary source: f’ = f(1 – u/v).
• Case 3: Source moving (u) toward a stationary observer: f’ = f / (1 – u/v).
• Case 4: Source moving (u) away from a stationary observer: f’ = f /(1 + u/v).