Refraction is the phenomenon when a wave changes direction due to a change in speed of the wave, most notably in response to the wave traveling from one medium to another. This is most commonly discussed in reference to the change in the path of a light beam, but affects other waves such as sound as well.
The rule which describes this change in direction is known as Snell's Law, which says that the proportion of the sines of the angles are equal to the inverse proportion of the indices of refraction and also to the proportion of the velocities.
sine theta1 / sine theta1 = n2 / n1 = v1 / v2
Also Known As: optical refraction