# Formula Snell's Law Refractive index of the 1st medium    Angle of incidence    Angle of refraction

## Refractive index of the 1st medium

Unit
Refractive index of one of the two media in which the light beam propagates. In vacuum, $$n_1 = 1$$.

## Refractive index of the 2nd medium

Unit
Refractive index of the second medium into which the light beam is refracted.

## Angle of incidence

Unit
Angle of incidence from the incident beam in the first medium. Measured relative to the normal (a line perpendicular to the surface).

## Angle of refraction

Unit
Angle of refraction of the incident beam in the second medium. Measured relative to the normal.