## Refractive Index and Snell's Law

Refraction is the change in direction of a wave that takes place at the interface between two media. The speed and the wavelength of the wave will also change, but the frequency will not. When light passes from a less dense medium to a denser medium, as below, it will be refracted towards the normal (the broken vertical line below).

Snell's law gives us a relationship between the angle of incidenceand the angle of refraction

The refractive index of the vacuum is taken to be 1. The refractive index of air is so nearly equal to 1 that it is often taken to be 1. If media 1 above is air, andis 30 degrees, and medai 2 is glass for which the refractive index is 1.4 then

Similar relationships hold for the wavelength:and the speed

If the wavelength in medium 1 in the above example is 2 cm thenand

The frequency is the same in both media.