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Constance of speed of light and refraction index question

  1. Sep 7, 2009 #1
    I'm new to the forum, so, hi =D

    Special theory of relativity tell us that the speed of light is the same, independently of the reference frame.

    But we know that, while light travels through some materials (with refraction index larger than one), it speeds slows down.

    These two "things" seems to have a contradiction to me. What's the explanation for that? (I think I'm making some confusion with these concepts)

    If someone can help me with that, I would be grateful.

    Thanks all
  2. jcsd
  3. Sep 7, 2009 #2


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    The speed of light in vacuum is the same no matter what the frame of reference. That does not say that the speed is not reduced when it is moving through something.

    (You can argue that, since all substances consist of a few atoms with vacuum between them, the speed of light is "c" between the atoms but it is "globally" slower than c because of the time required for the atoms to absorb and re-emit the light.)
  4. Sep 7, 2009 #3
    Is that also true assuming light not in vacuum (and the reference frames in the same material too)?
  5. Sep 8, 2009 #4


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

  6. Sep 8, 2009 #5
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