# Snell's law

The fundamental law that governs the refraction of light is Snell's Law. According to Snell's Law, when a light ray is transmitted into a new medium, the relationship between the angle of incidence (θ_{i}) and the angle of refraction (θ_{r}) is given by the following equation

**n _{i} sin(θ_{i}) = n_{r} sin(θ_{r})**

where the n_{i} and n_{r} values represent the refractive indexes (which are unitless) of the incident and the refractive medium respectively.

**Figure 1:** The incident and the refractive angles according to Snell's law.