Snell's Law

Snell's Law describes how the direction of light changes when it moves from one medium to another. The two forms of the law are:

<math> n_1 sin(\theta _1) = n_2 sin(\theta _2) </math>
<math> v_2 sin(\theta _1) = v_1 sin(\theta _2) </math>

where n1 and n2 are the indices of refraction in medias 1 and 2, respectively, and <math> \theta _1 </math> and <math> \theta _2 </math> is the angle from the normal of the plane dividing the 2 media and the ray.

The index of refraction of a material is inversely proportional to the speed of light in that material, i.e. light will move slower in a material with a high index of refraction than it will in a material with a low index of refraction.

What Snell's Law says is that when light moves from a medium with a high index of refraction to a medium with a low index of refraction it will bend away the normal of the plane dividing the two media. Conversely, when light moves from a medium with a low index of refraction to a medium with a high index of refraction it will bend towards from the normal dividing the two media.