Dispersion of light

A beam of light, passing through a triangular prism, deviates to a face lying opposite to the refracting angle of the prism. However, if it is a beam of white light, then, after it passes through the prism, it not only deviates, but also decomposes into colored beams. This phenomenon is called the dispersion of light. It was first studied by Isaac Newton in 1666 in a series of remarkable experiments.

The source of light in Newton's experiments was a small round hole located in the shutter of a window lit by the rays of the Sun. When a prism was installed before the hole, a colored strip appeared on the wall instead of a circular spot, called Newton's spectrum. This spectrum consists of seven main colors: red, orange, yellow, green, blue, blue and violet, which gradually changed into one another. Each of them occupies a space of different sizes in the spectrum. The longest is the purple band, the smallest is the red one.

The next experiment consisted of the emergence of narrow beams of a certain color from a wide beam of colored rays obtained with a prism, a screen with a small aperture, and directed toward the second prism.

The prism deflecting them does not change the color of these rays. Such rays are called simple or monochromatic (monochromatic).

Experience shows that the red rays experience a smaller deviation than the violet ones, i.e. Rays of different colors are unequally refracted by the prism.

Collecting a lens of colored beams of rays emerging from the prism, Newton received a white image of the hole on a white screen instead of a colored strip.

Of all the experiments carried out, Newton made the following conclusions:

• White light by its nature is a complex light, which consists of colored rays;
• The rays of light of different chromaticity have different refractive indices of matter; As a result, when a white light beam is deflected by a prism, it decomposes into a spectrum;
• If you combine the colored rays of the spectrum, you will again get white light.

Thus, the dispersion of light is a phenomenon that is caused by the dependence of the refractive index of a substance on the wavelength (or frequency).

The dispersion of light is noted not only when light passes through the prism, but also in various other cases of refraction of light. Thus, in particular, the refraction of sunlight in drops of water is accompanied by its decomposition into multi-colored rays, this explains the formation of the rainbow.

Newton used a rather wide cylindrical beam of sunlight to guide the spectrum through a circular hole made in the shutter.

The spectrum obtained in this way is a series of multicolored images of a circular hole partially overlapping one another. In order to obtain a more pure spectrum, when studying the phenomenon of light dispersion, Newton proposed using a narrow slit parallel to the refracting edge of the prism, not a circular hole. Using a lens, a clear image of the slit is obtained on the screen, after which a prism is installed behind the lens, which gives the spectrum.

The most pure and bright spectra are obtained with the help of special instruments - spectroscopes and spectrographs.

Absorption of light is a phenomenon in which the energy of a light wave decreases as it passes through matter. This is due to the transformation of the energy of a light wave into the energy of secondary radiation or, in other words, the internal energy of a substance that has a different spectral composition and other directions of propagation.

Absorption of light can cause heating of matter, ionization or excitation of molecules or atoms, photochemical reactions, as well as other processes in matter.