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index of refraction

 
Dictionary: index of refraction

n.
The ratio of the speed of light in a vacuum to the speed of light in a medium under consideration. Also called refractive index.


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Computer Desktop Encyclopedia: refractive index
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A property of a material that changes the speed of light, computed as the ratio of the speed of light in a vacuum to the speed of light through the material. When light travels at an angle between two different materials, their refractive indices determine the angle of transmission (refraction) of the light beam. In general, the refractive index varies based on the frequency of the light as well, thus different colors of light travel at different speeds. High intensities also can change the refractive index.

The refractive index of a vacuum is 1.0, and air is a tiny fraction greater than 1.0. The higher the index, the slower the speed of light through the medium, because the speed through the material is the speed of light (c) over the refractive index (n), thus speed = c/n. Following are common refractive indices. See fiber optics glossary.

                    Refractive
  Material          Index (n)

  Vacuum            1.0
  Air               1.0 (tiny fraction more than 1)
  Water             1.33
  Glass             1.45-1.48
  Lithium niobate   2.25
  Gallium arsenide  3.35
  Silicon           3.5
  Germanium         4.0

Refractive Indices
When light travels at an angle between two materials, light bends according to their refractive indices. In order to reflect, light must be on the wider side of the critical angle.

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WordNet: index of refraction
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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: the ratio of the velocity of light in a vacuum to that in a medium
  Synonym: refractive index


 
 

 

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
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