Refrakt

Refrakt is the phenomenon in which a wave changes direction as it passes from one medium to another with a different propagation speed. In optics, this most commonly refers to light, but refraction also occurs with sound, water, and seismic waves. The underlying cause is that the speed of the wave is different in the two media, which changes its angle of travel at the boundary.

The behavior is described by Snell's law: n1 sin(theta1) = n2 sin(theta2), where theta1 and theta2 are the angles of incidence and refraction with respect to the normal to the boundary, and n1 and n2 are the refractive indices of the two media. The refractive index n is the ratio of the speed of light in vacuum to the speed in the medium (n = c/v). A wave speeds up or slows down when entering a new medium, causing its path to bend toward or away from the normal accordingly.

Dispersion is a common consequence of refrakt: different wavelengths travel at different speeds and bend by different amounts, producing effects such as rainbows. Total internal reflection can occur when light travels from a medium with higher refractive index to one with a lower index and the incident angle exceeds a critical value, causing the wave to reflect entirely rather than refract.

Applications of refraction include corrective lenses, cameras and eyeglasses, prisms that separate light into colors, and fiber-optic communications. In everyday life, refraction is seen in a straw appearing bent in a glass of water or the apparent depth of a submerged object.