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Homework Help: Special Relativity

  1. Jun 1, 2010 #1

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    Last edited: Jun 1, 2010
  2. jcsd
  3. Jun 2, 2010 #2
    Please post the question in the required format. It's not even clear what the question is.
  4. Jun 19, 2010 #3
    The speed of light is slowed in water. Does it return to its former speed when emerging from the water?
  5. Jun 21, 2010 #4
    The short answer is yes, the propagation speed of light in air is greater than in water both before and after it goes through the water. But the actual speed of a photon, is always c.

    The reason light appears to slow down in air and travel even slower in water is that the photons do not take a straight uninterrupted path through a medium. Each photon is absorbed and re-emitted many times along the way, so that the average propagation speed of light in a medium is less than c.

    The ratio between c and the speed that light propagates through a medium is its refractive index, which is about 1.0003 for air and about 1.333 for water for visible light, hence the slower propagation speed of light in water than in air.
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