Today we’ll talk about what radiation is in physics. We will tell about the nature of electronic transitions and give an electromagnetic scale.
Deity and atom
The structure of matter has become the subject of interest of scientists more than two thousand years ago. Ancient Greek philosophers wondered how air differs from fire, and earth from water, why marble is white and coal is black. They created complex systems of interdependent components, refuted or supported each other. And the most incomprehensible phenomena, for example, a lightning strike or sunrise, were attributed to the action of the gods.
One day, for many years observing the steps of the temple, one scientist remarked: each foot that stands on a stone carries away a tiny particle of matter. Over time, the marble changed shape, caved in the middle. The name of this scientist is Leucippus, and he called the smallest particles atoms, indivisible. From this began the path to the study of what radiation is in physics.
Easter and light
Then came the dark times, science was abandoned. All who tried to study the forces of nature were dubbed witches and sorcerers. But, strangely enough, it was religion that gave impetus to the further development of science. The study of what radiation is in physics began with astronomy.
The time of the celebration of Easter was calculated in those times each time differently. The complex relationship between the vernal equinox, the 26-day lunar cycle, and the 7-day week did not allow the preparation of date tables for Easter for more than a couple of years. But the church had to plan everything in advance. Therefore, Pope Leo X ordered the compilation of more accurate tables. This required careful observation of the motion of the moon, stars and the sun. And in the end, Nikolai Copernicus realized: the Earth is not flat and not the center of the universe. A planet is a ball that revolves around the sun. And the Moon is a sphere in the orbit of the Earth. Of course, one may ask: “What does all this have to do with what radiation is in physics?” We’ll open it now.
Oval and beam
Later, Kepler supplemented the Copernican system, establishing that the planets move in oval orbits, and this movement is uneven. But it was precisely that first step that instilled in humanity an interest in astronomy. And there was not far from the question: “What is a star?”, “Why do people see its rays?” and "How is one luminary different from another?" But first you have to move from huge objects to the smallest. And then we come to radiation, a concept in physics.
Atom and raisins
At the end of the nineteenth century, enough knowledge was accumulated about the smallest chemical units of matter - atoms. It was known that they are electrically neutral, but contain both positively and negatively charged elements.
There were many assumptions: both that positive charges are distributed in a negative field, like raisins in a bun, and that an atom is a drop from heterogeneous charged liquid parts. But everything clarified the experience of Rutherford. He proved that in the center of the atom is a positive heavy nucleus, and light negative electrons are located around it. And the configuration of the shells for each atom is different. This is where the characteristics of radiation lie in the physics of electronic transitions.
Boron and orbit
When scientists found that the light negative parts of an atom are electrons, another question arose - why didn’t they fall on the nucleus. Indeed, according to Maxwell's theory, any moving charge radiates, therefore, loses energy. But atoms existed as long as the universe, and were not going to annihilate. Bor came to the rescue. He postulated that the electrons are in some stationary orbits around the atomic nucleus, and can only be on them. The transition of an electron between orbits is carried out in a jerk with the absorption or emission of energy. This energy can be, for example, a quantum of light. In fact, we have now set forth the definition of radiation in particle physics.
Hydrogen and photography
Initially, photography technology was invented as a commercial project. People wanted to stay for centuries, but not everyone could afford to order a portrait from the artist. And the photos were cheap and did not require such a large investment. Then the art of glass and silver nitrate placed itself at the service of military affairs. And then science began to take advantage of photosensitive materials.
First of all, spectra began to be photographed. It has long been known that hot hydrogen emits specific lines. The distance between them obeyed a certain law. But the spectrum of helium was more complex: it contained the same set of lines as hydrogen, and one more. The second series no longer obeyed the law deduced for the first series. Here the theory of Bohr came to the rescue.
It turned out that there is only one electron in the hydrogen atom, and it can transfer from all higher excited orbits to one lower one. This was the first series of lines. Heavier atoms are more complex.
Lens, grating, spectrum
Thus, the beginning of the application of radiation in physics was laid. Spectral analysis is one of the most powerful and reliable methods for determining the composition, quantity and structure of a substance.
- The electronic emission spectrum will tell you what is contained in the object and what is the percentage of a component. This method is used by absolutely all fields of science: from biology and medicine to quantum physics.
- The absorption spectrum will tell which ions and at what positions are present in the lattice of a solid.
- The rotational spectrum will demonstrate how far the molecules are inside the atom, how many and what bonds each element has.
And the ranges of application of electromagnetic radiation and not count:
- radio waves explore the structure of very distant objects and the bowels of the planets;
- thermal radiation will tell about the energy of processes;
- visible light will tell you in which directions the brightest stars lie;
- ultraviolet rays will make it clear that high-energy interactions are occurring;
- The X-ray spectrum itself allows people to study the structure of matter (including the human body), and the presence of these rays in space objects will notify scientists that the neutron star, supernova burst, or black hole is in the focus of the telescope.
Black body
But there is a special section that studies what thermal radiation is in physics. Unlike atomic, thermal light emission has a continuous spectrum. And the best model object for calculations is a completely black body. This is such an object that “catches” all the light falling on it, but does not release it back. Oddly enough, a completely black body radiates, and the maximum wavelength will depend on the temperature of the model. In classical physics, thermal radiation gave rise to the paradox of ultraviolet disaster. It turned out that any heated thing had to radiate more and more energy, while in the ultraviolet range its energy would not destroy the universe.
Max Planck was able to resolve the paradox. He introduced a new quantity, a quantum, into the radiation formula. Without giving her any special physical meaning, he discovered the whole world. Quantization of quantities is now the basis of modern science. Scientists realized that fields and phenomena consist of indivisible elements, quanta. This has led to deeper studies of matter. For example, the modern world belongs to semiconductors. Previously, everything was simple: metal conducts current, other substances are dielectrics. And substances like silicon and germanium (just semiconductors) behave incomprehensibly with respect to electricity. To learn how to manage their properties, it was necessary to create a whole theory and calculate all the possibilities of pn transitions.