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N=c/v=λ0/λ (T doesn't change) and v of light is constant

  1. Jan 15, 2012 #1
    n=c/v=λ0/λ (T doesn't change) and v of light is constant in a specific medium(i.e. the ratio is constant in given mediums), so the index of refraction is constant for all light when changing mediums.

    If we say that index of refraction differs according to the wavelength, then there is contradiction with the above formula n=c/v that says n is constant in specific medium
  2. jcsd
  3. Jan 15, 2012 #2
    Re: dispersion(optics)

    what i meant to ask is that the formula n=c/v shows that the index is constant for all light and depends only on the medium. however while explaining the dispersion, they say that the index of refraction depends on the wavelength of every light.

    isn't there a contradiction?

    thanks for answering
  4. Jan 15, 2012 #3


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    Re: dispersion(optics)

    The phase velocity of the material, v, is dependent upon the wavelength.
  5. Jan 15, 2012 #4
    Re: dispersion(optics)

    do u mean that the velocity of light in a specific medium is not constant and differs according to the wavelength???

    for example do x-rays and radio waves have different speeds in glass?
  6. Jan 15, 2012 #5


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    Re: dispersion(optics)

    Yes. You don't even need to go that extreme; violet and red wavelengths have different speeds in glass.

    Here is a graph of n vs. λ for several different types of glass: visible wavelengths are shown by the pink band:

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