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What determines the colour? Frequency or wavelenght?

  1. Jul 25, 2004 #1
    What determines the colour? Frequency or wavelenght?
  2. jcsd
  3. Jul 25, 2004 #2

    Normally high frequencies correspond to small wavelengths, and this correspond to colours that are blue-shifted. In the EM-spectrum blue is high energy, and red is low energy. these colors come from the EM-variant of the Doppler-effect. An EM-spectrum can be "made" when reflected sunlight from a planet undergoed emission or absorption processes when passing through our atmosphere. So we will see lines that move to blue when a planet is moving towards us. lines will be moved to red when the planet moves away from us. This is the EM-Dopplereffect.
  4. Jul 25, 2004 #3


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    Frequency times wavelength is the speed of light, so they are inversely related and either of them can be used.
  5. Jul 31, 2004 #4
    That's not a complete answer: the wavelength depends also on the medium through which the light passes. The color we see is determined by the frequency.
  6. Aug 4, 2004 #5
    It depends on the energy of the photons our retina cells receive. This energy would be [tex]E = hf[/tex] or [tex]E = hv/\lambda_{eye fluid}[/tex], with h plank's constant, and [tex]v = c/n_{eye fluid}[/tex] is the speed of light through the fluid in our eye.
  7. Aug 4, 2004 #6

    Doc Al

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    Just a note: The energy of a photon depends on its frequency, which does not change when light passes from one medium to another.
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