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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.
Descartes' third model creates a mathematical equation for the Law of Refraction, characterized by the angle of incidence equalling the angle of refraction. 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 ...
Let the angle of refraction, measured in the same sense, be θ t, where the subscript t stands for transmitted (reserving r for reflected). In the absence of Doppler shifts, ω does not change on reflection or refraction. Hence, by , the magnitude of the wave vector is proportional to the refractive index.
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 refractive index determines how much the path of light is bent, or refracted , when entering a material.
Snell's Law can be used to predict the deflection of light rays as they pass through "linear media" as long as the indexes of refraction and the geometry of the media are known. For example, the propagation of light through a prism results in the light ray being deflected depending on the shape and orientation of the prism.
The angle between this ray and the normal is known as the angle of refraction, and it is given by Snell's law. Conservation of energy requires that the power in the incident ray must equal the sum of the power in the refracted ray, the power in the reflected ray, and any power absorbed at the surface.