Laws of Refraction

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• The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane.
• For any two given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
• The above law is called Snell's law after the scientist Willebrod Snellius who first formulated it

Thus

Where m is the refractive index of the second medium with respect to the first medium.

We know that the phenomenon of refraction is taking place because the speed of light changes when it is travelling from one optical medium to another.

Thus we can define refractive index in terms of the speed of light in the two media.

The refractive index of glass with respect to air is given by the relation.

In general, if a ray of light is passing from medium 1 to medium 2, then

If the medium 1 is air or vacuum, the refractive index of medium 2 is referred to as the absolute refractive index.

The refractive index of a medium depends on the following factors:

• the nature of the medium
• the colour or wavelength of the incident light