How to use Refractive index in a sentence
It is there shown that every substance, transparent to light, has a definite refractive index, which is the ratio of the velocity of light in vacuo to its velocity in the medium to which the refractive index refers.
According to the electromagnetic theory of light K = N2, where N is the refractive index for rays of infinite wave-length.
In the case of substances possessing anomalous dispersion, the direct measurement of the refractive index for Hertzian waves of very long wave-length may be employed.
Calling the refractive index µ, we have as the critical value of e=2Xo/ µ sin a, (1).
The limit can be depressed only by a diminution in Xo, such as photography makes possible, or by an increase in /2, the refractive index of the medium in which the object is situated.Advertisement
Taking the refractive index of water for the red rays as 0;, and for the violet rays as 1 r, we can calculate the following values for the minimum deviations corresponding to certain assigned values of n.
On the other hand, while in the older crown and flint glasses the relation between refraction and dispersion had been practically fixed, dispersion and refraction increasing regularly with the density of the glass, in some of the new glasses introduced by Abbe and Schott this relation is altered and a relatively low refractive index is accompanied by a relatively high dispersion, while in others a high refractive index is associated with low dispersive power.
This is probably never completely attained, variations in the sixth significant figure of the refractive index being observed in different parts of single large blocks of the most perfect glass.
As a general rule, to which, however, there are important exceptions, both these qualities are found to a greater degree, the lower the refractive index of the glass.
In this table n is the refractive index of the glass for sodium light (the D line of the solar spectrum), while the letters C, F and G' refer to lines in the hydrogen spectrum by which dispersion is now generally specified.Advertisement
There are very few substances, however, for which the optical refractive index has the same value as K for steady or slowly varying electric force, on account of the great variation of the value of K with frequency.
If the powder of a transparent substance is immersed in a liquid of the same refractive index, the mixture becomes transparent and a measurement of the refractive index of the liquid gives the refractivity of the powder.
Christiansen found, in an investigation of this kind, that the refractivity of the liquid could only be got to match that of the powder for mono-chromatic light, and that, if white light were used, brilliant colour effects were obtained, which varied in a remarkable manner when small changes occurred in the refractive index of the liquid.
If the refractive index is, for instance, the same for both in the case of green light, and a source of white light is viewed through the mixture, the green component will be completely transmitted, while the other colours are more or less scattered by multiple reflections and refractions at the surfaces of the powdered substance.
Wood, when white light is transmitted through a paste made of powdered quartz and a mixture of carbon bisulphide with benzol having the same refractive index as the quartz for yellow light.Advertisement
Wood has studied the iridescent colours seen when a precipitate of potassium silicofluoride is produced by adding silicofluoric acid to a solution of potassium chloride, and found that they are due to the same cause, the refractive index of the minute crystals precipitated being about the same as that of the solution, which latter can be varied by dilution.
The equations finally arrived at are DX2(A2_ 2) (x2_ A2m)2+g2A2 ' DgA3 (A A l m) 2 +g 2 A2 ' where is the wave-length in free ether of light whose refractive index is n, and A m the wave-length of light of the same period as the electron, is a coefficient of absorption, and D and g are constants.
Liquid prisms, however, suffer from the fact that any change of temperature involves a change in the refractive index of the prism.
An immediate deduction from Maxwell's theory was that in transparent dielectrics, the dielectric constant or specific inductive capacity should be numerically equal to the square of the refractive index for very long electric waves.
Maxwell made a comparison between the optical refractive index and the dielectric constant of paraffin wax, and the approximation between the numerical values of the square of the first and that of the last was sufficient to show that there was a basis for further work.Advertisement
On the other hand, the divergence in some cases between the square of the optical refractive index and the dielectric constant was very marked.
Our atmosphere is a medium of continuously varying refractive index.
Differences of refractive index produce their greatest dispersive effects when incidence on the refracting surface is nearly tangential.
They are formed now on one side, now on the other, of the absorption line; but the rapid increase of refractive index which accompanies true anomalous dispersion, and might be expected to produce similar bands by scattering the light, appears both from theory and experiment to belong to the side of greater wave-length exclusively.
The polarizing angle varies from one transparent substance to another, and Sir David Brewster in 1815 enunciated the law that the tangent of the polarizing angle is equal to the refractive index of the substance.Advertisement
In the contrary case, total reflection commences as soon as sin i =µ 1, µ being still the relative refractive index of the more highly refracting medium; and for greater angles of incidence r becomes imaginary.
This is made by fixing a thin crystalline plate between two glass prisms turned in opposite directions by a cement of the same refractive index as the glass.
This refractive index should be equal to the greatest index of the plate, and with a biaxal plate the mean axis of optical symmetry should be parallel to its faces and in the normal section of the prisms, while with an uniaxal plate the optic axis should be in a plane perpendicular to this normal section.
To reduce the aberrations Sir David Brewster proposed to employ in the place of glass transparent minerals of high refractive index and low dispersion.
The value of the clearness of an image-point in a median section is the sine of the semi-aperture of the pencil multiplied with the refractive index of the medium.Advertisement
In dry-systems only the sine of the semi-aperture is concerned; in immersion-systems it is the product of the refractive index of the immersion-liquid and the sine of the object-side semi-aperture.
The value n sin u equals the numerical aperture A, where n is the refractive index of the immersion-liquid, and u is the semi-aperture on the object-side.
The advantages of the immersion over the dry-systems are greatest when the embedding-liquid, the glass cover, the immersion-liquid and the front lens have the same refractive index.
Cedarwood oil (Canada balsam), which has a refractive index of 1.515, is the immersion-liquid.
In order to determine the refractive index when the thickness of the crystal is known, or the thickness of the crystal when the index is known, a fine adjustment A makes it possible to measure exactly the changes in the length of the microscope.Advertisement
Therefore, all that is needed to produce a sensitive refractive index sensor is a sensitive measure of the rotation of the polarization ellipse.
This is usually done by coating them in a material of lower refractive index than the fiber.
Light is guided in the core of the fiber that has a higher refractive index than the cladding by total internal reflection.
The slower propagation of light in gas or water than in air or vacuum may be attributed to a greater density, or to a less rigidity, in the former case; or we may adopt the more complicated supposition that both these quantities vary, subject only to the condition which restricts the ratio of velocities to equality with the known refractive index.
The "dielectric constant" of a medium is its specific inductive capacity, and on the electromagnetic theory of light it equals the square of its refractive index for light of infinite wave length (see Electrostatics; Magneto-Optics).Advertisement
Thus this figure is not the actual physical depth of the coverslip but one modified by the refractive index of the glass itself.
Both natural and lab-created stones have the same hardness, specific gravity, refractive index and dispersion factor."