—refractional, adj./ri frak"sheuhn/, n.1. Physics. the change of direction of a ray of light, sound, heat, or the like, in passing obliquely from one medium into another in which its wave velocity is different.2. Ophthalm.a. the ability of the eye to refract light that enters it so as to form an image on the retina.b. the determining of the refractive condition of the eye.3. Astron.a. Also called astronomical refraction. the amount, in angular measure, by which the altitude of a celestial body is increased by the refraction of its light in the earth's atmosphere, being zero at the zenith and a maximum at the horizon.b. the observed altered location, as seen from the earth, of another planet or the like due to diffraction by the atmosphere.[1570-80; < LL refraction- (s. of refractio). See REFRACT, -ION]
* * *Change in direction of a wave as it leaves one medium and enters another.Waves, such as sound and light waves, travel at different speeds in different media. When a wave enters a new medium at an angle of less than 90°, the change in speed occurs sooner on one side of the wave than on the other, causing the wave to bend, or refract. When water waves approach shallower water at an angle, they bend and become parallel to the shore. Refraction explains the apparent bending of a pencil when it is partly immersed in water and viewed from above the surface. It also causes the optical illusion of the mirage.
* * *▪ physicsin physics, the change in direction of a wave passing from one medium to another caused by its change in speed. For example, waves in deep water travel faster than in shallow; if an ocean wave approaches a beach obliquely, the part of the wave farther from the beach will move faster than that closer in, and so the wave will swing around until it moves in a direction perpendicular to the shoreline. The speed of sound waves is greater in warm air than in cold; at night, air is cooled at the surface of a lake, and any sound that travels upward is refracted down by the higher layers of air that still remain warm. Thus, sounds, such as voices and music, can be heard much farther across water at night than in the daytime.The electromagnetic waves constituting light are refracted when crossing the boundary from one transparent medium to another because of their change in speed. A straight stick appears bent when partly immersed in water and viewed at an angle to the surface other than 90°. A ray of light of one wavelength, or colour (different wavelengths appear as different colours to the human eye), in passing from air to glass is refracted, or bent, by an amount that depends on its speed in air and glass, the two speeds depending on the wavelength. A ray of sunlight is composed of many wavelengths that in combination appear to be colourless; upon entering a glass prism, the different refractions of the various wavelengths spread them apart as in a rainbow.
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