Index of refraction below one

  • Thread starter Robert_G
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  • #1
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Main Question or Discussion Point

Hi, there.

I don't understand how the light travel in the medium which has the index of refaction below one

from the following topic:
http://en.wikipedia.org/wiki/Total_external_reflection

“For X-rays, however, all materials have indices of refraction slightly below 1. ”

I did some calculations before, for same light pulse, in certain materials, the index of fraction do have a value smaller than 1.

Does this mean the light is travelling faster than c?
 

Answers and Replies

  • #2
maajdl
Gold Member
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Yes the phase velocity is larger than c.
Yet, it is still impossible to transmit information or any "effect" faster than c.

Read about: dispersion, group velocity, ...
Materials are necessary dispersive because the interaction with light necessarily depends on the frequency (color).
 
  • #3
Simon Bridge
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Last edited:

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