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Index of Refraction
Excerpt from Field Guide to Spectroscopy
The speed of light in a transmitting medium is less than that of the speed of light in a vacuum. The index of refraction, n, is the ratio of the speed of light in a vacuum, c, to the speed of light in a medium, c':
One consequence of this difference in speed is that when light goes from one medium to another at an angle, the propagation vector in the new medium has a different angle with respect to the normal.
n1 sinθ1 = n2 sinθ2
This relationship is called Snell's law.
Indices of refraction are temperature-dependent and wavelength-dependent.
Indices of refraction of common materials*
|flint glass||1.55||rock salt||1.544|
*for light having a wavelength of ~550-590 nm