refractive index
Sign in to saveratio of the speed of light in vacuum to that in the medium
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The refractive index is a number that describes how much a material slows down light compared to how fast light travels in empty space. It matters because it determines how much light bends when entering a material, which is why objects look different underwater or through glass than they do in air.
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Article
A ray of light being refracted through a glass slab Refraction of a light ray
In optics, the refractive index (also called refraction index or index of refraction), often denoted n, is the ratio of the speed of light in vacuum (c) to the speed of light in a given optical medium (v), n=c/v. The refractive index determines how much the path of light is bent, or refracted, when entering a material, as described by Snell's law of refraction, n1 sin θ1 = n2 sin θ2, where θ1 and θ2 are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices n1 and n2. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection, their intensity (Fresnel equations) and Brewster's angle.