Snell's Law is about how light rays alter its direction when it travels from one medium to the other. When light travels from one medium to other it undergoes refraction. The ratio of the sines of the angles of incidence and refraction is constant for all incidences in any given pair of media for electromagnetic waves of a definite frequency when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air. This law of refraction (Snell's law) states that :
- The incident ray i, the refracted ray r and the normal N for the given surface at a point of incidence lies in the same plane
- For any pair of medium, the sine angle of incidence i to the sine angle of refraction r ratio is constant ($\mu$).
Snell's law formula for the given pair of media is given by
Where, $\mu$ is the refractive index value of second medium with respect to first called as n21