The Index of Refraction

The Index of Refraction

As discussed on the previous page, light will travel at different speeds in different media. The speed of light in vacuum is represented by c:

c = 2.99792458 x 10⁸m/s

Light will never travel faster than this value, which is generally rounded to 3.00 x 10⁸ m/s. The amount by which light slows in a given material is described by the index of refraction, n. The index of refraction of a material is defined by the speed of light in vacuum c divided by the speed of light through the material v:

n = c/v

The index of refraction of some common materials are given below.

material	n	material	n
Vacuum	1.0000	Crown Glass	1.52
Air	1.0003	Salt	1.54
Water	1.33	Asphalt	1.635
Ethyl Alcohol	1.36	Heavy Flint Glass	1.65
Fused Quartz	1.4585	Diamond	2.42
Whale Oil	1.460	Lead	2.6

Values of n come from the CRC Handbook of Chemistry and Physics

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