The refractive index (coefficient) is called a certain abstract number, which characterizes the refractive power of any transparent medium. It is accepted to designate it with the Latin letter n. There are absolute refractive index and relative coefficient.
The first is calculated according to 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 ray of light 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 its speed of propagation at the moment of transition from vacuum to a transparent medium. Thus, the refractive index (absolute) is determined. In order to find out the relative, use the formula:
n = n 2 / n 1.
That is, the absolute refractive indices of substances of different densities, 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:
- the refractive index of glass (crowns) - 1.5163;
- air - 1,000292;
- glycerol - 1,473;
- ether 1.358;
- ethyl alcohol - 1.333;
- 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 parameter is 1.334.
Since the wavelength is an indicator, of course, inconstant, an index is assigned to the letter n. Its value also helps to understand what wave of the spectrum this coefficient refers to. When considering the same substance, but with an increase in the wavelength of the light, the refractive index will decrease. This circumstance is caused by the decomposition of light into a spectrum when passing through a lens, a prism, etc.
By the value of the refractive index, it is possible to determine, for example, how much one substance is dissolved in another. This can be useful, for example, in brewing or when it is necessary to find out the concentration of sugar, fruit or berries in 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, you need 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 closes .
Without using any substance, the scale visible in the eyepiece of the device will be completely painted in blue. If you drip onto the prism of ordinary distilled water, when the instrument is correctly calibrated, the border of blue and white will go strictly at zero. In the study of another substance, it will shift on a scale according to what index of refraction is characteristic of it.