The law of refraction establishes a relationship between the angle of incidence, the angle of refraction and the relative refractive index of two media. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for these two media, equal to the ratio of the speeds of light in these media. The incident ray, the refracted ray and the perpendicular raised to the surface at the point of incidence of the ray lie in the same plane.
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