# Snell's law

formula deriving the angle of refraction of light between two mediums
(Redirected from Refractive index)

Snell's Law of Refraction is the scientific law of the refraction of light or other waves. In optics, Snell's law is about the speed of light in different media. The law states that when light passes through different materials (for example from air to glass) the ratio of sines of the incidence (incoming) angle and the refraction (outgoing) angle does not change:

${\frac {\sin \theta _{1}}{\sin \theta _{2}}}={\frac {v_{1}}{v_{2}}}={\frac {n_{2}}{n_{1}}}$ With each $\theta$ as the angle measured from the normal of the boundary, $v$ as the velocity of light in the respective medium (SI units are meters per second, or m/s). $n$ is the refractive index of the medium.
The index of refraction of a vacuum is 1 and the velocity of light in a vacuum is $c$ . When a wave passes the material where the index of refraction is n, the velocity of the wave becomes ${\frac {c}{n}}$ .