Refraction

Refraction is the change in the direction in which waves travel when they pass from one kind of matter into another. Waves are refracted (bent) when they pass at an angle from one medium into another in which the velocity of light is different. A pencil standing in water looks broken at the water line because light travels slower in water than in air. The amount that a ray of a certain wavelength bends in passing from one medium into another is indicated by the index of refraction (n) between the two mediums for that wavelength. Finding n is a problem in trigonometry. It is a function of the sines of the angles of incidence and refraction:

n equals sin i divided by sin r. This formula is also called Snell's Law after the Dutch mathematician Willebrord Snell van Royen (1591-1626), who formulated the law.

Common indexes of refraction depend on the relationship of a ray's angle in air to its angle in such mediums as glass, quartz, or plastic. The different colors in light are not refracted to the same extent. Because of this characteristic of light, refracted light beams often break up into the colors of the spectrum. A prism works on this principle.

Contributor: Joseph A. Muscari, Ph.D., Program Manager, Martin Marietta.

See also Lens; Light; Mirage; Prism; Rainbow; Sound.

Refraction

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