How the refractive index is calculated

An index (refractive index) is an abstract number that characterizes the refractive power of a transparent medium. It is denoted by the letter n. Distinguish between the absolute refractive index and the relative coefficient.

The first is calculated by one of two formulas:

N = sin α / sin β = const (where sin α is the sine of the angle of incidence, and sin β is the sine of the angle of refraction of the light beam entering the medium from the void)

or

N = c / υ _λ (where c is the speed of light in the void, υ _λ is the speed of light in the medium under study).

Here the calculation shows how many times the light changes the speed of its propagation at the moment of transition from vacuum to transparent medium. Thus, the refractive index (absolute) is determined. To find out the relative, use the formula:

N = n ₂ / n _1.

That is, in this case, absolute refractive indices of substances of different density, for example air and glass, are considered.

Generally speaking, the absolute coefficients of any bodies, whether gaseous, liquid or solid, are always greater than 1. Basically, their values range from 1 to 2. Above 2, this value can only be in exceptional cases. The value of this parameter for some environments:

• Refractive index of glass (crowns) - 1,5163;
• Air - 1.000292;
• Glycerol 1,473;
• Ether - 1.358;
• Ethyl alcohol - 1.363;
• Carbon disulphide - 1.629;
• Of organic glass - 1.49.

This value in application to the hardest natural substance on the planet, diamond, is 2.42. Very often during scientific research, etc., it is required to know the index of refraction of water. This parameter is 1.334.

Since the wavelength is an indicator, of course, unstable, an index is assigned to the letter n. Its meaning also helps to understand to which wave spectrum the given coefficient refers. When considering the same substance, but with increasing light-wave length, the refractive index will decrease. This circumstance also causes the decomposition of light into the spectrum as it passes through a lens, a prism, and so on.

By the magnitude of the refractive index, you can determine, for example, how many one substance is dissolved in another. This is useful, for example, in brewing or when you need to know the concentration of sugar, fruit or berries in juice. This indicator is important in determining the quality of petroleum products, and in jewelry, when you need to prove the authenticity of the stone, etc.

To determine the refractive index, a special device called a refractometer is used. In order to use it, first of all it is necessary to clean it with a soft cloth, and then apply 2-3 drops of the test substance to the prism entering the structure. Further, a special plate for daylight is closed .

Without the use of any substance, the scale visible in the eyepiece of the device will be completely colored blue. If you drip on the prism of ordinary distilled water, with the correct calibration of the instrument, the border of blue and white colors will pass strictly at zero. In the study of another substance, it will move along a scale according to the index of refraction that is inherent in it.