Snell's Law (redirected from Snells law)

Snell's law: see refraction.

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Snell's law

Relationship between the path taken by a ray of light as it moves from one medium to another and the refractive indices of the two media. Discovered in 1621 by Willebrord Snell (1580–1626), the law went unpublished until its mention by Christiaan Huygens. If n₁ and n₂ represent the indices of refraction of two media, and θ₁ and θ₂ are the angles of incidence and refraction that a ray of light makes with the line perpendicular to the boundary (the normal), Snell's law states that n₁/n₂ = sin θ₂/sin θ₁. Because the ratio n₁/n₂ is a constant for any given wavelength of light, the ratio of the two sines is also a constant for any angle.

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Snell’s Law 

a law governing the refraction of a beam of light at the boundary between two transparent media. It asserts that the ratio sin α /sin β is constant for the same two media; here, α is the angle of incidence of the beam on the boundary, and β is the angle of refraction.

The law was established by W. Snell around 1620 and by R. Descartes in 1637. The discovery of Snell’s law permitted the completion of the foundations of geometrical optics and made possible the formulation of Fermat’s principle. The law provided the basis for the introduction of the concept of the refractive index of a medium. In terms of refractive indexes, Snell’s law can be written in the form sin α/sin β = n₂/n₁ where n₁ and n₂ are the refractive indexes of the first and second media, respectively, through which the light travels. (See alsoREFRACTION OF LIGHT.)