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Confusion about the speed of light

  1. Sep 2, 2012 #1
    So everyone knows the speed of light is a universal constant. However in many phenomena involving light it is useful to think that light is 'slowing down' like light travels slower in glass/ water then it does in a vacuum. How can this be if it is a universal constant?
  2. jcsd
  3. Sep 2, 2012 #2


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    Speed of light in vacuum is universal constant. Light passing through media interacts with media and slows down.
  4. Sep 2, 2012 #3
    There is a bit about this in the FAQ;

    https://www.physicsforums.com/showthread.php?t=511177 [Broken]
    Last edited by a moderator: May 6, 2017
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