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Snell's law (also known as the Snell–Descartes law, the ibn-Sahl law, [1] and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. [1] Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave ...
The ordinary law of refraction was at that time attributed to René Descartes (d. 1650), who had tried to explain it by supposing that light was a force that propagated instantaneously, or that light was analogous to a tennis ball that traveled faster in the denser medium, [44] [45] either premise being inconsistent with Fermat's.
A ray of light being refracted through a glass slab Refraction of a light ray. In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium.
The law of refraction says that the refracted ray lies in the plane of incidence, and the sine of the angle of incidence divided by the sine of the angle of refraction is a constant: =, where n is a constant for any two materials and a given colour of light.
In today's notation, the law of refraction states, sin i = n sin r , where i is the angle of incidence, r is the angle of refraction, and n is the index of refraction. Using a tennis ball, Descartes would compare the projection of a ray of light to the way a ball moves when it is thrown up against another object.
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle. Refraction is the bending of light rays when passing through a surface between one transparent material and another. It is described by Snell's Law:
From Snell's law it can be seen that the angle of refraction of light in a prism depends on the refractive index of the prism material. Since that refractive index varies with wavelength, it follows that the angle that the light is refracted by will also vary with wavelength, causing an angular separation of the colors known as angular dispersion.