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Why are some materials transparent?

  1. May 29, 2012 #1
    Hey! I just saw a video on youtube from the guys at nothingham university (sixty symbols) where they explained that some materials are transparent due to the energy gap between the excited states of the electrons in the material. If photons come in at lower energies they will not interact with the material and pass right trough. The video is found here:

    However, if the photons pass right trough, how come the speed of light slows down in for example glass? I've heard that the reason that this happens is precisely because the photons get absorbed and reemitted.

    Both quantum and classical explenations are appreciated.
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. May 29, 2012 #2


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    Please start by reading the FAQ sub forum in the General Physics forum.

  4. May 29, 2012 #3
    Thanks Zz, your explanation there were illuminating. Do you know if there are some classical approaches for explaining the apparent slowing down of the speed of light, reflection and transmittion?
  5. May 31, 2012 #4
    You could look into light scattering theory
    - https://www.physicsforums.com/showthread.php?p=3772953
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