The Doppler Effect for light
Key point
- When the source of light approaches, then the frequency increases and the wavelength decreases
The Doppler Effect for light proposes that when the source of light approaches, then the frequency increases and the wavelength decreases.
- When the wavelength decreases then we call that a blue-shift
- When the source of light moves away from the observer, then the frequency decreases and the wavelength increases – we call that a red-shift
Formula Booklet
The equation of the doppler effect for light is significantly more complicated than for sound, however, for small speed of the source (relative to the speed of light) we can simply:
- v = speed of source or the observer
- c = speed of light
- f = emitted frequency
- Δf = change in observed frequency
- λ = emitted wavelength
- Δλ = change in observed wavelength
The light coming from galaxies shows a red-shift. This supports the argument of the ‘expanding universe’
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