1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Refractive index

  1. Aug 15, 2015 #1
    Hi
    1)Does refractive index varies when we are dealing with different waves? for example the refractive index for a typical glass is 1.5 when a visible light passes through it. Does it the same for x rays?
    2) there is a complex formula which describes the refractive index: n = 1- δ - iβ. how is the proof of this formula?
     
  2. jcsd
  3. Aug 15, 2015 #2
    1) Yes refractive index of a material varies with wavelength of the radiation incident on it.

    Can't answer the 2nd question.
     
  4. Aug 15, 2015 #3
    Refractive index changes with variation of waves, yes. And that formula looks familiar, I think I saw it in Feynman's lecture in physics, but I don't think the proof was given there, the proof may be too complex.
     
  5. Aug 15, 2015 #4

    vanhees71

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    A quite simple model for the dielectric function of a homogeneous material (and thus the refraction index) is to assume a completely classical system of bound charges, which are only slightly disturbed by the incoming electromagnetic wave and thus linear-response theory is applicable. So you can just assume that the charges of the material are bound harmonically and have some "friction" (dissipation). It's a bit lengthy to work this out here. You find an excellent treatment of this classical dispersion theory in

    A. Sommerfeld, Lectures on theoretical physics, vol. 4 (optics)
     
  6. Aug 15, 2015 #5

    blue_leaf77

    User Avatar
    Science Advisor
    Homework Helper

    In general, refractive index can be complex, i.e. ##n=n_R+i\hspace{0.5mm}n_I##. This is because refractive index is defined as the square root of permittivity, while permittivity is a complex quantity.
    $$
    n=\sqrt{\epsilon} = \sqrt{1+\chi} = \sqrt{1+\chi_R+i\hspace{0.5mm}\chi_I}
    $$
    So, it's no surprise that you would find something like you wrote there.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook