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Index of Refraction

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.

This change in direction of propagation is called refraction. The relationship between the indices of refraction and the angles is

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*

^{*for light having a wavelength of ~550-590 nm}