Irradiationthermal is the term used to say that some body is being exposed to thermal radiation. Thermal irradiation is one of the main processes of transferinheat, this process occurs through the issueinelectromagnetic waves, since all the bodies that are in temperatures above of absolute zero emit thermal radiation. In this type of process, part of the bodies' thermal energy is converted into electromagnetic energy and vice versa.
Lookalso:Thermology - study of phenomena related to heat and temperature
How thermal radiation occurs
THE radiationthermal is generated from the movements of vibrationFromatomsand molecules, the basic constituents of all matter. Unlike other processes of heat transfer, like driving and convection, irradiation can occur without the need for a physical medium to conduct heat, and this is only possible because electromagnetic waves can propagate in the vacuum.
When absorbed, thermal radiation heats bodies. However, there are bodies that can absorb it more easily. Factors such as
color, the chemical composition and energy levels of the atoms directly affect the heat absorption capacity. An example of this is dark clothing, which heats up more quickly than light clothing, thanks to its greater capacity to absorb heat when radiated.Do not stop now... There's more after the advertising ;)
Irradiation and radiation
while the word radiation refers to energy that is emitted in the form of electromagnetic waves, the irradiation refers to exposureto this radiation. For example: solar radiation radiates the planet Earth, providing it with energy in the form of heat and visible light. The word irradiation relates to the word radiation in the same way as magnetism relates to magnetization, for example.
Lookalso: 7 Questions Physics Hasn't Answered
Irradiation and electromagnetic waves
Not all electromagnetic waves carry heat. At waveselectromagnetic whose frequencies are found in regions close to the frequencies of the colorred It's from infra-red they are moreefficient to the transferinheat than the others. Furthermore, it is known that the way in which electromagnetic waves interact with matter depends on their frequency.
Check out the most common effects that each type of electromagnetic wave can cause to matter:
- Microwave: have a long wavelength when they interact with matter and can cause atoms and molecules perform rotational movements, as occurs with water molecules inside an oven microwave.
- Infra-red: is almost completely absorbed by matter, this type of electromagnetic wave is responsible for most of the heat transmission. When it interacts with matter, infrared causes atoms and molecules to vibrate with greater intensity.
- Visible light: distributed between frequencies ranging from red to violet, it is capable of promoting the excitation of electrons. These frequencies of light are capable of stimulating changes in the energy levels of atoms.
- Ultraviolet: like visible light, it promotes electron excitation, however, the higher ultraviolet frequencies are ionizing, that is, because of their high energy, they become capable of ripping electrons from their atoms.
- X ray: promote the ionization of atoms and also Compton scattering, in this phenomenon, the atoms that absorb X-rays re-emit it at lower frequencies.
- Gamma: electromagnetic waves with high penetration power and highly capable of ionizing atoms and molecules.
When exposed to infrared radiation, atoms and molecules absorb it, causing their thermal vibration to increase. At electrical charges that are present in atoms also vibrate, so this radiation is re-emitted towards other bodies.
There is not even a moment when we do not exchange heat, in the form of electromagnetic waves, with the bodies around us. According to what the Zero Law of Thermodynamics, this exchange occurs until the condition of thermal balance.
Lookalso:Electromagnetic spectrum - the possible frequencies of electromagnetic waves
black body radiation
One bodyblack it is an idealized object, that is, it is a theoretical proposition. According to theory, a black body must be able to absorb all the radiation falling on its surface. Once this body reaches the balancethermal between its parts, it will issue radiationthermal at the same rate at which it absorbs it.
In nature, there are no ideal black bodies, however, there are those that are very close to this situation, such as stars, capable of absorbing all the radiation that falls on them.
Thanks to the explanations of important physicists such as JosephStefan and LudwigBoltzmann, today we can directly relate the power radiated by the surface of black bodies with their temperature, just as thermometers do. laser, called pyrometers.
In addition, there are physical laws, such as the law of Wien, which relate the frequency of electromagnetic waves emitted in the form of thermal radiation with the temperature of the body that emitted them. It was through these laws that we were able to estimate the temperature and age of stars and extremely distant planets.
Studies of black body radiation have gone beyond the Stefan-Boltzmann laws and of the lawinWien. In search of a solution to a seemingly insoluble problem, the German physicist Max Planck suggested the existence of small packets of light, the photons (which were called quanta of light). In season, Planck he was heavily criticized and his suggestion was not well accepted in academia. However, in 1905, Albert Einstein made use of this argument to explain the photoelectric effect, which earned him the Nobel Prize in Physics.
By Me. Rafael Helerbrock
Would you like to reference this text in a school or academic work? Look:
HELERBROCK, Rafael. "Thermal irradiation"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/irradiacao-termica.htm. Accessed on June 27, 2021.
