In life, we are constantly faced with dispersion, but we do not always notice it or even sometimes do not know what it is. Now we will try to consider in more detail what constitutes dispersion. Her first striking example is the usual rainbow. There is hardly a person who would never have admired this beautiful phenomenon. According to old legend, at the foot of the rainbow you can find a pot full of gold. We are so used to seeing a rainbow that it seems ordinary to us, and we do not delve into its nature. In fact, each of its appearance is accompanied by complex physical processes, which we will try to understand in this article.
In the most general sense, dispersion is the refraction of light. Passing through a prism, a ray of light refracts and decays into different colors. This can be easily checked at home. Let's have a little experience. On a sunny day, it is necessary to close the window with a dense curtain and make a small hole in it through which a narrow beam will penetrate into the room. A light spot will form on the wall opposite the window from the beam. We put a glass prism in the path of the beam. Now we can make sure that dispersion is a condition for the appearance of a rainbow, because the spot on the wall has become multi-colored. In it you can see all the colors of the rainbow, from red to purple.
Thus, dispersion is an optical phenomenon caused by the dependence of the refractive index of a substance on the frequency of light (wavelength) or on the dependence of the phase velocity of light waves on its frequency or wavelength. The result of dispersion is the decomposition of a light beam into a spectrum as it passes through a glass prism. The dispersion of light was discovered in 1672 by Newton, who was actively studying the spectrum.
Newton was not the first to conduct such experiments. Already at the beginning of our era, it was known that light was decomposed into a spectrum when it passed through large single crystals. The first researchers to refract light were the English scientist T. Hariot and the Czech natural scientist J. Marzi, but it was Newton who began to seriously analyze this process.
Newton conducted a whole series of experiments and experiments with prisms. The results of his research were described in detail in Lectures on Optics, Optics, and The Theory of Light and Colors. Newton was able to prove that white light is not at all fundamental to all the others, but on the contrary, it is heterogeneous. Various types of dispersion, that is, the decomposition of white light into its component parts, appear when a ray passes through various prisms and groups of prisms. The decomposition of light occurs because each color has a certain degree of refraction. Each color has its own specific properties. Dispersions clearly show their difference. The studies performed by scientists are of great interest to modern physicists in terms of not only results, but also methodology. Starting his research, Newton set the task not to put forward hypotheses, but to explain the properties of light by facts and reasoning. The scientist made many experiments, noting that "the abundance of experiments does not interfere."
By directing a ray of light on a glass prism, Newton could see a kind of rainbow on the screen. The scientist identified seven primary colors that we all know well now. Why exactly seven? It was seven colors that were the brightest. In addition, there are only seven notes in music, but their variations allow you to create real works of art that are different from each other. Then he conducted a reverse experiment, directing the spectrum to the edge of another glass prism. At the same time, a white light came out again. As a result, Newton came up with the idea to create a circle with seven sectors of different colors, during the rotation of which white light will again be obtained.
Thus, dispersion is a complex physical process due to the properties of light and color. And it is thanks to this process that we can observe a rainbow after a thunderstorm. Now you have a scientific understanding of the causes of the appearance of the rainbow.