Refraction of Light

Refraction of Light

 

the change in the direction of the propagation of light upon its passage through the interface between two mediums. At an unbounded plane interface between homogeneous, isotropic, nonabsorbing (transparent) mediums with the refractive indexes n1 and n2, the refraction of light is defined by two regularities. First, the refracted ray lies in the plane passing through the incident ray and the normal (perpendicular) to the interface surface; second, the angles of incidence Φ and of refraction x (see Figure 1) are related by Snell’s law, which states n1 sin Φ = n2 sin X.

Figure 1. The path of light rays upon refraction at a plane surface dividing two transparent mediums. The broken line represents the reflected ray. The angle of refraction is greater than the angle of incidence. This indicates that medium 1 is optically less dense than medium 2. Thus, n1 < n2. The normal to the surface of the interface is designated by n.

The refraction of light is accompanied by the reflection of light. In this case, the sum of the energies of the refracted and reflected pencils of light, whose quantitative expression follows from Fresnel’s equations, is equal to the energy of the incident pencil of rays. Their relative intensities depend on the angle of incidence, the values of n1 and n2, and the polarization of light in the incident pencil of rays. In the case of normal incidence, the ratio of the average energies of the refracted and the incident light waves is equal to 4n1n2/(n1 + n2)2. In the important, particular case of light passing from air (n1 = 1 to a high degree of accuracy) into glass with n2 = 1.5, this quantity is 96 percent.

If n2 < n1 and if the angle of incidence Φ ≥ arc sin (n2/n1), refraction of light does not occur, and the entire energy of the incident light wave on the interface is transferred to the reflected wave (total reflection). At any value of Φ, with the exception of Φ = 0, the refraction of light is accompanied by a change in the state of polarization of the light; this change is strongest at the Brewster angle Φ = arc tan (n1/n2). The phenomenon is used in obtaining plane-polarized light. The dependence of the refraction of light on the polarization of incident rays is clearly seen in double refraction in optically anisotropic mediums.

The same equations are used in formal descriptions of the indexes of refraction of both absorbing and nonabsorbing mediums. In treating absorbing mediums, however, n is regarded as a complex quantity, the imaginary part of which characterizes the absorption of light by the medium. In this case, x also becomes complex and loses the meaning of a simple angle of refraction that it has for nonabsorbing mediums. In general, n of a medium depends on the wavelength of light X; for this reason, the component rays of nonmonochromatic light with various X travel along different paths when refracted (dispersion of light).

The laws governing the refraction of light form the basis for the configuration of lenses and many optical devices used to change the direction of light rays and to obtain optical images.

REFERENCES

Landsberg, G. S. Optika, 4th ed. Moscow, 1957. (Obshchii kurs fiziki, vol. 3.)
Born, M., and E. Wolf. Osnovy optiki, 2nd ed. Moscow, 1973. (Translated from English.)

N. A. VOTSHVILLO

References in classic literature ?
It is merely the effect of the MIRAGE," said the doctor, "and nothing else--a simple optical phenomenon due to the unequal refraction of light by different layers of the atmosphere, and that is all.
They are produced by refraction of light from mineral and ice crystals, from mist, rain, spray, and no end of things; and I am afraid they are the penalty I must pay for transparency.
Each material was crafted to frame the perfectly cut centre diamond as a way to maximise the reflection and refraction of light.
But he is misled by the view: Due to the refraction of light on the surface, he does not see the actual location of the fish.
A dirty windshield can be very dangerous for motorists, especially at night as it reduces visibility since dust and grime make the windshield hazy and leads to refraction of light.
While rainbows arise from the refraction of sunlight through raindrops, circumzenith arcs are the refraction of light through ice crystals.
Elsewhere, they are illusionistic upshots of quick paint application, as with the runny cobalt trails just described, or result from the opening up of space through the application of a piece of foil that garishly revels in the refraction of light.
The index of refraction of water takes into account the refraction of light at the cuvette wall.
In essence, the design (right) is a drum filled with water and light that when tapped, creates a refraction of light and evokes the way moonlight is reflected on water.
Iridescence - a lustrous rainbow-like play of colour caused by differential refraction of light waves - has just been detected in the fur of golden moles.
controlling the refraction of light between the LCD and the screen.