Radiation is a physical process that results in the transfer of energy through electromagnetic waves. The radiation reverse process is called absorption. We consider this question in more detail, and also give examples of radiation in everyday life and nature.
Physics of radiation
Any body consists of atoms, which, in turn, are formed by positively charged nuclei and electrons that form the electron shells around the nuclei and are negatively charged. Atoms are arranged in such a way that they can be in different energy states, that is, possess both greater and lesser energy. When an atom has the smallest energy, they speak of its ground state, any other energy state of the atom is called excited.
The existence of various energy states of an atom is due to the fact that its electrons can be located at various energy levels. When an electron moves from a higher level to a lower one, the atom loses the energy that it radiates into the surrounding space in the form of a photon - a carrier particle of electromagnetic waves. On the contrary, the transition of an electron from a lower to a higher level is accompanied by the absorption of a photon.
There are several ways to transfer an atom’s electron to a higher energy level, which involve the transfer of energy. This can be either the impact on the atom in question of external electromagnetic radiation, or the transfer of energy to it by mechanical or electrical means. In addition, atoms can receive and then release energy as a result of chemical reactions.
Electromagnetic spectrum
Before moving on to examples of radiation in physics, it should be noted that each atom emits certain portions of energy. This is because the states in which an electron can be in an atom are not arbitrary, but strictly defined. Accordingly, the transition between these states is accompanied by the emission of a certain amount of energy.
It is known from atomic physics that photons generated as a result of electronic transitions in an atom have an energy that is directly proportional to their oscillation frequency and inversely proportional to the wavelength (a photon is an electromagnetic wave that is characterized by propagation speed, length and frequency). Since the atom of matter can only emit a certain set of energies, it means that the wavelengths of the emitted photons are also specific. The set of all these lengths is called the electromagnetic spectrum.
If the wavelength of the photon lies between 390 nm and 750 nm, then they speak of visible light, since people can perceive it with their own eyes, if the wavelength is less than 390 nm, then such electromagnetic waves have high energy and are called ultraviolet, x-ray or gamma radiation. For lengths greater than 750 nm, a small photon energy is characteristic, they are called infrared, micro- or radio emissions.
Thermal radiation from bodies
Any body that has a temperature other than absolute zero radiates energy, in this case they speak of thermal or temperature radiation. In this case, the temperature determines both the electromagnetic spectrum of thermal radiation and the amount of energy emitted by the body. The higher the temperature, the more energy the body radiates into the surrounding space, and the more its electromagnetic spectrum shifts to the high-frequency region. The processes of thermal radiation are described by the laws of Stefan-Boltzmann, Planck and Wien.
Examples of radiation in everyday life
As mentioned above, absolutely any body radiates energy in the form of electromagnetic waves, however, this process can not always be seen with the naked eye, since the temperatures of the bodies around us are usually too small, so their spectrum lies in the low-frequency region invisible to humans.
A striking example of radiation in the visible range is an electric incandescent lamp. Passing in a spiral, the electric current heats the tungsten filament to 3000 K. Such a high temperature causes the filament to emit electromagnetic waves, the maximum of which falls on the long-wavelength part of the visible spectrum.
Another example of radiation in everyday life is a microwave oven, which emits microwaves invisible to the human eye. These waves are absorbed by objects containing water, thereby increasing their kinetic energy and, as a result, temperature.
Finally, an example of household radiation in the infrared range is the radiator of a heating battery. We do not see its radiation, but we feel this warmth.
Natural emitting objects
Perhaps the most striking example of radiation in nature is our star - the Sun. The temperature on the surface of the Sun is about 6000 K, therefore, its maximum radiation emission occurs at a wavelength of 475 nm, that is, lies within the visible spectrum.
The sun heats the planets around it and their satellites, which also begin to glow. It should distinguish between reflected light and thermal radiation. So, our Earth can be seen from space in the form of a blue ball precisely thanks to the reflected sunlight. If we talk about the thermal radiation of the planet, then it also takes place, but lies in the region of the microwave spectrum (about 10 microns).
In addition to reflected light, it is interesting to give another example of radiation in nature, which is associated with crickets. The visible light emitted by them is in no way associated with thermal radiation and is the result of a chemical reaction between atmospheric oxygen and luciferin (a substance contained in insect cells). This phenomenon is called bioluminescence.