The Doppler effect
You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect.
When a source moves towards an observer, the observed wavelength decreases and the frequency increases.
When a source moves away from an observer, the observed wavelength increases and the frequency decreases.
The Doppler effect
You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect.
When a source moves towards an observer, the observed wavelength decreases and the frequency increases.
When a source moves away from an observer, the observed wavelength increases and the frequency decreases.
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