Refraction is the change in direction of a wave due to a change in its transmission medium. Refraction is a surface phenomenon. It is in agreement with the law of conservation of energy and momentum. Due to the change of medium, the phase velocity of the wave is changed but its frequency remains constant. This principle is commonly observed when a wave passes from one medium to another any angle besides 90o and 0o.
Refraction of light is the most commonly observed phenomenon but any type of wave can refract when it interacts with a medium. For example, when sound waves pass from one medium into another or when water waves move into water of a different depth.
Refraction is described by Snell’s law. This law states that for a given pair of media and a ave with a single frequency, the ration of the sines of the angle of incidence ϴ1 and angle of refraction ϴ2 is equivalent to the ratio of phase velocities in the two media or equivalent to the opposite ratio of the indices of refraction. The equation is as followed
sinϴ1/sinϴ2 = v1/v2 = n2/n1
The incident wave is partially refracted and partially reflected. This behavior can be described by the Fresnel equations.