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Refraction
Physical phenomenon relating to the direction of waves / From Wikipedia, the free encyclopedia
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 is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/8/85/Refraction_photo.png/640px-Refraction_photo.png)
For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence and angle of refraction
is equal to the ratio of phase velocities
in the two media, or equivalently, to the refractive indices
of the two media:[2]
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/Snells_law.svg/640px-Snells_law.svg.png)
Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelength of light,[3] and thus the angle of the refraction also varies correspondingly. This is called dispersion and causes prisms and rainbows to divide white light into its constituent spectral colors.[4]
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