the law that, for a ray incident on the interface of two media, the sine of the angle of incidence times the index of refraction of the first medium is equal to the sine of the angle of refraction times the index of refraction of the second medium.
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British Dictionary definitions for Snell's law
physics the principle that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant when a light ray passes from one medium to another
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