# Refractive index

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The **refractive index** is the measurement that tells us how much a medium will slow down light or other waves. For example, typical glass has a refractive index of 1.5, which means that light travels at 1 / 1.5 = 0.67 times the speed in a vacuum.

Definition: *The refractive index (n) of a medium is defined as the ratio of the velocity (c) of a wave such as light or sound in a medium to the velocity of the wave in a vacuum.*

The formula for calculating refractive index is as follows:

- n = Speed of light in vacuum/Speed of light in given material - where n is refractive index. The speed of light in a vacuum will always be constant.

## Snell's law Edit

Snell's law allows the refractive index of a material to be found by relating the angle of incidence and angle of refraction of a light beam passing through the material. Snell's law is as follows:

In this formula, n is the refractive index of the material, i is the angle of incidence and r is the angle of refraction.