Doppler Effect Calculator
Observed Freq (Approaching)
—
Observed Freq (Receding)
—
Frequency Shift (Approaching)
—
Frequency Shift (Receding)
—
Understanding the Doppler Effect
The Doppler effect describes how the observed frequency of a wave changes when the source and observer move relative to each other. When approaching, the observed frequency is higher (sounds higher-pitched); when receding, it's lower. The formula is f' = f × (c ± v_o) / (c ∓ v_s).
The effect is named after Austrian physicist Christian Doppler who proposed it in 1842. It applies to all waves: sound, light, and even water waves. For sound in air, the speed of sound is about 343 m/s at 20°C.
Real-world applications include radar speed guns, medical ultrasound, astronomical redshift measurements, and weather radar. The familiar change in pitch of a passing ambulance siren is a classic demonstration of the Doppler effect.
Frequently Asked Questions
What is the Doppler effect?
The change in observed wave frequency due to relative motion between source and observer. Approaching = higher frequency; receding = lower frequency.
What is the Doppler formula for sound?
f' = f × (c + v_observer) / (c - v_source) for approaching. Signs reverse for receding. c is the speed of sound.
Does the Doppler effect apply to light?
Yes. Stars moving away from us appear redshifted (lower frequency). Stars approaching appear blueshifted. This is how we know the universe is expanding.
What is a sonic boom?
When a source exceeds the speed of sound (v_s > c), it creates a shock wave — a sonic boom. The Doppler formula breaks down at this point.