Snell's law gives the relationship between angles of incidence and refraction for a wave impinging on an interface between two media with different indices of refraction. The law follows from the boundary condition that a wave be continuous across a boundary, which requires that the phase of the wave be constant on any given plane, resulting in

(1)

where and are the angles from the normal of the incident and refracted waves, respectively.

Angle of Incidence, Angle of Refraction, Brewster's Angle, Critical Angle, Fermat's Principle, Ray Parameter, Refraction