Doppler effect — Science definition
The change in observed frequency (pitch) when a wave source and observer move relative to each other.
Where it is taught
- Sound — Waves, Sound & Optics, Physics & Environmental Science, Grade 12
In use
The Doppler effect compares emitted and received frequency.
Sound
Questions using doppler effect
Problem 1
Explain the Doppler effect using a passing ambulance siren as your example.
Answer and explanation
As the ambulance approaches, its sound waves bunch together in front of it, shortening the wavelength and raising the frequency, so you hear a higher pitch. As it passes and moves away, the waves stretch out, lowering the frequency, so the pitch drops. That falling pitch as it goes by is the Doppler effect.