Refraction. It is the bending of a light ray when it crosses the boundary between two different materials, as from air into water. This change in direction is due to a change in speed. Light travels fastest in empty space and slows down upon entering matter. Its speed in air is almost the same as its speed in space, but it travels only 3/4 as fast in water and only 2/3 as fast in glass. The refractive index of a substance is the ratio of the speed of light in space (or in air) to its speed in the substance. This ratio is always greater than one.
When a beam of light enters a pane of glass perpendicular to the surface (above), it slows down, and its wavelength in the glass becomes shorter in the same proportion. The frequency remains the same. Coming out of the glass, the light speeds up again, the wavelength returning to its former size.
When a light ray strikes the glass at some other angel, it changes direction as well as speed. Inside the glass, the ray ends toward the perpendicular or normal. If the two sides of the glass are parallel, the light will return to its original direction when it leaves the glass, even though it has been displaced in its passage. If the two sides of the glass are not parallel, as in the case of a prism or a lens, the ray emerges in a new direction. [pg. 42]
Laws of Refraction
1. Incident and refracted rays lie in the same plane.
2. When a ray of light passes at an angle into a denser medium, it is bent toward the normal, hence the angle of refraction (r) is smaller than the angle of incidence (i)...
3. The index of refraction of any medium is the ratio between the speed of light in a vacuum (or in air) and its speed in the medium. [pg. 43]
The Index of Refraction [n] determines the amount of bending of a light ray as it crosses the boundary from air into the medium. [pg. 43]
[Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971.
R E F E R E N C E S
Refract vt [L refractus, pp. of refringere to break open, break up, fr. re- + frangere to break --more at Break] [1612] 1a: to subject [as a ray of light] to refraction b: to alter or distort as if by refraction [to _ that familiar world through the mind and heart of a romantic . . . woman -Anton Myrer] 2: to determine the refracting power of
Refraction n [1603] 1: deflection from a straight path undergone by a light ray or energy wave in passing obliquely from one medium [as air] into another [as glass] in which its velocity is different 2: the change in the apparent position of a celestial body due to bending of the lgiht rays emanating from it as they pass through the atmosphere; also: the correction to be applied to the apparent position of a body because of this bending 3: the action of distorting an image by viewing through a medium; also: an instance of this.
Refractive adj [1673] 1: having power to refract 2: relating or due to refraction
[Merriam-Webster's Collegiate Dictionary, 10th Edition. Springfield, MA, USA: Merriam-Webster, Inc. 1995.]
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