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refraction





refraction
Refraction of a light ray on entering and leaving a glass block
The bending of light from its original path as it passes from one transparent material to another with a different refractive index. This index is defined as equal to 1 in a vacuum. For any other medium it is defined as the speed of light in a vacuum divided by the speed of light in the medium. Thus refraction occurs when the speed of light is different in the two media. The amount of bending depends on the media involved and the frequency of the light.

The angle of refraction also depends on the light's frequency. Different frequencies refract at slightly different angles – a phenomenon known as dispersion. The most familiar example is the dispersion of white light into a spectrum of colors when it is passed through a prism.

The effect of refraction is used in the design of lenses and prisms, and of combinations of lenses such as eyepieces and refracting telescopes. In nature, refraction causes objects appear higher in the sky than they otherwise would. Objects more than halfway from the horizon to the zenith (i.e., with an altitude greater than 45°) are almost totally unaffected; however, objects near the horizon can be shifted by a degree or so. It is also responsible for the well-known phenomena of rainbows, mirages, and atmospheric haloes.


Related entries

   • double refraction
   • refractive index


Related category

   • OPTICS AND OPTICAL PHENOMENA