How the refractive index is calculated

Science 2023
How the refractive index is calculated
How the refractive index is calculated

The refractive index is some abstract number that characterizes the refractive power of a transparent medium. It is customary to designate it with the Latin letter n. Distinguish between the absolute refractive index and the relative coefficient.

The first is calculated using 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 under consideration from the void)


n=c / υλ (where c is the speed of light in vacuum, υλis the speed of light in the medium under study).

refractive index

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

n=n2 / n1.

That is, the absolute refractive indices of substances of different densities are considered,such as air and glass.

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 be only in exceptional cases. The value of this parameter for some environments:

  • refractive index of glass

    refractive index of glass (crown) - 1, 5163;

  • air - 1, 000292;
  • glycerin - 1, 473;
  • ether - 1, 358;
  • ethyl alcohol - 1, 363;
  • carbon disulfide - 1,629;
  • organic glass - 1, 49.

This value, when applied to the hardest natural substance on the planet, diamond, is 2.42. Very often when conducting scientific research, etc., it is required to know the refractive index of water. This setting is 1, 334.

Since the wavelength is, of course, a non-constant indicator, an index is assigned to the letter n. Its value helps to understand which wave of the spectrum this coefficient refers to. When considering the same substance, but with increasing wavelength of light, the refractive index will decrease. This circumstance caused the decomposition of light into a spectrum when passing through a lens, prism, etc.

refractive index of water

The value of the refractive index can be used to determine, for example, how much of 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 the juice.This indicator is important both in determining the quality of petroleum products, and in jewelry, when it is necessary to prove the authenticity of a 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 included in the design. Next, a special plate for daylight is closed.

Without the use of any substance, the scale visible in the eyepiece of the instrument will be completely blue. If you drop ordinary distilled water on a prism, with the correct calibration of the instrument, the border of blue and white colors will pass strictly along the zero mark. When examining another substance, it will shift along the scale according to its refractive index.

Popular topic