Dismiss Notice
Join Physics Forums Today!

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


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    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

    User Avatar

    Staff: Mentor

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

Have something to add?

Similar Discussions: What determines the colour? Frequency or wavelenght?
  1. What is Colour? (Replies: 2)