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Refraction

When light moves from one medium to another, it changes direction, i.e. it is refracted. If it moves from a medium with refractive index n to one with refractive index n, with an incidence angle to the surface normal of θ, the refraction angle θ can be calculated from Snell's law: n 1 sin θ 1 = n 2 sin θ 2. {\displaystyle n_{1}\sin \theta _{1}=n_{2}\sin \theta _{2}.}

When light enters a material with higher refractive index, the angle of refraction will be smaller than the angle of incidence and the light will be refracted towards the normal of the surface. The higher the refractive index, the closer to the normal direction the light will travel. When passing into a medium with lower refractive index, the light will instead be refracted away from the normal, towards the surface.