Refraction definitions and example sentences on Wordnik

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noun The turning or bending of any wave, such as a light or sound wave, when it passes from one medium into another of different optical density.
noun Astronomy The apparent change in position of celestial objects caused by the bending of light rays entering Earth's atmosphere.
noun Medicine The ability of the eye to bend light so that an image is focused on the retina.

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The act of refracting, or the state of being refracted: almost exclusively restricted to physics, and applied to a deflection or change of direction of rays, as of light, heat, or sound, which are obliquely incident upon and pass through a smooth surface bounding two media not homogeneous, as air and water, or of rays which traverse a medium the density of which is not uniform, as the atmosphere. It is found (1) that, when passing into a denser isotropic medium, the ray is refracted toward the perpendicular to the surface, and bent away from it when passing into one less dense; (2) that the sines of the angles of incidence and refraction bear a constant ratio to each other for any two given media; and (3) that the incident ray and the refracted ray are in the same plane. Thus, if (fig. 1) SP represents a ray incident upon the surface of water at P, it will be bent away from its original direction SPL toward the perpendicular Qq in passing into the denser medium, and make an angle q PR, such that the is a constant quantity—that is, the perpendicular distance of a point q (such that the line from it to P, the point of incidence, is normal to the surface) from the refracted path bears a constant ratio to its distance from the path as it would be without refraction, however the angle of incidence varies; but this constant depends on the nature of the two media. If the first medium is air, this constant ratio is called the index of refraction or refractive index of the given substance (or n). Again, if the ray proceeded from R to P, it would be bent away from the perpendicular in the direction PS. The latter case is peculiar, however, in that for a certain angle of incidence called the critical angle (whose sine =1 n) the angle of refraction of QPS is a right angle and a ray incident at P at any greater angle cannot pass out into the rarer medium at all, but suffers total reflection at P. In fig. 2, AHC is the angle of incidence, and EHK the angle of refraction, CD being the normal to the surface; if, further, the second surface is parallel to the first, the ray emerging into the original medium at E has a direction EF parallel with its first direction, AH. If (fig. 3) the refracting medium has the form of a prism (ABC), the incident ray LF suffers a double change of direction, first (FE) in passing into the prism, and second (EG) in emerging from it; the total angle of deviation IDL varies in value with a change in the direction of LF, but has a definite minimum value when the angles of incidence and emergence are equal. If d represents the angle of the prism BAC, and r the angle of minimum deviation, LDI, then the refractive index n of the material of which the prism is made is given by the relation The angle of deviation or refraction also increases as the wave-length of the ray diminishes, and hence a beam of white light in passing through a prism is both refracted and dispersed, thus yielding a spectrum. The phenomena of the refraction of light explain the properties of lenses (see lens) and of prisms (see prism and spectrum). Sound-waves may also be refracted when passing from one medium to another of different density, obeying the same laws as light Double refraction is the separation of a ray of light into two rays, which are unequally refracted upon passing through an anisotropic medium. This property belongs to all transparent crystalline substances except those of the isometric system. A striking example is calcite, hence called doubly refracting spar. In uniaxial crystals (those belonging to the tetragonal and hexagonal systems) one of the rays follows the ordinary law of refraction (see law (2), above), and is called the ordinary ray; the other, which does not, is called the extraordinary ray; both rays are polarized (see polarization), the ordinary ray having vibrations perpendicular to and the extraordinary ray vibrations parallel to the vertical axis. If the index of refraction is greater for the ordinary ray than for the extraordinary ray, the crystal is said to be negative, and in the opposite case positive: otherwise expressed, a crystal is negative or positive according as the crystallographic axis (optical axis) is the axis of greatest or of least elasticity. In the direction of the vertical axis a ray suffers no double refraction, and this direction is called the optic axis. In biaxial crystals (those belonging to the orthorhombic, monoclinic, and triclinic systems) neither ray follows the ordinary law of refraction, and there are two directions, called optic axes, lying in the plane of the axes of greatest and least elasticity, in which a ray suffers no double refraction. There are also three indices of refraction, corresponding to the rays propagated by vibrations parallel to the three axes of elasticity. A biaxial crystal is called negative or positive according as the acute bisectrix coincides with the axis of greatest or of least elasticity. According to the degree of difference between the two indices of refraction of a uniaxial crystal and between the greatest and least of the three indices of a biaxial crystal, the double refraction is said to be strong or weak; upon this difference depends the brilliancy of color of thin sections of a crystal as seen in polarized light. Amorphous substances like glass do not show double refraction, except under abnormal conditions, as when subjected to unequal strains, as in glass suddenly cooled. This is also true of crystals belonging to the isometric system, which, however, sometimes show secondary or abnormal double refraction (as garnet), due to internal molecular strain or other cause. For the refraction of the eye, see eye, and crystalline humor (under crystalline). Errors of refraction in the eye are tested by trial with lenses, test types, etc., by the ophthalmoscope, or by skiascopy or the shadow-test, and are corrected by appropriate glasses.
In logic, the relation of the Theophrastian moods to the direct moods of the first figure.
Astronomical or atmospheric refraction the apparent angular elevation of the heavenly bodies above their true places, caused by the refraction of the rays of light in their passage through the earth's atmosphere, so that in consequence of this refraction those bodies appear higher than they really are. It is greatest when the body is on the horizon, and diminishes all the way to the zenith, where it is zero.

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So to be completely invisible, you need to eliminate reflection and refraction -- and that brings us to the speed of light. — F ;SF; - vol 093 issue 02 - August 1997
When physicists are talking about the speed of light in a particular material, they talk about the index of refraction -- the ratio of the speed of light in a vacuum to the speed of light in a material. — F ;SF; - vol 093 issue 02 - August 1997
Since the index of refraction is a ratio of two speeds, it's a number without units. — F ;SF; - vol 093 issue 02 - August 1997
He went carefully into the question of refraction, the importance of which Tycho had been the first astronomer to recognise, though he only applied it at low altitudes, and had not arrived at a true theory or accurate values. — Kepler
Index of Refraction • To calculate the exact angle of refraction, we need to know the c index of refraction "n" n = • The index of v refraction is the speed of light in a vacuum (c) divided by the speed of light in "stuff" (v) — Recently Uploaded Slideshows

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