The Sun is the largest natural source of thermal radiation in the solar system.
Thermal radiation is the energy emitted in the form of electromagnetic waves by a body due to its temperature. It is the result of the movement of charged particles within matter, and all bodies with temperatures above absolute zero emit thermal radiation.
Examples of Thermal Radiation
Thermal radiation is a common phenomenon in nature and technology, and can be observed in various contexts:
- the Sun : emits energy in the form of light and heat due to its high temperature. This radiation travels through space and reaches Earth, providing the energy necessary for life and the climate;
- a stove or fireplace : when lighting a stove or fireplace, the heat we feel from a distance is thermal radiation. Incandescent firewood or coal emits this energy due to its high temperature;
- The human body : The bodies of all living beings emit thermal radiation in the form of infrared radiation. Devices such as thermal cameras can capture this radiation to create images based on temperature differences;
- Electric heaters : An electric resistance heater generates thermal radiation. By heating a filament or surface, the device emits heat into the environment, affecting objects and the surrounding air;
- Earth : The Earth's surface, which absorbs solar radiation during the day, also emits thermal radiation in the form of infrared energy into space. This phenomenon is fundamental for the thermal balance of the planet and is related to the greenhouse effect.
A fireplace emits thermal radiation, transferring heat in the form of electromagnetic waves that heat the nearby environment.
Fundamentals of thermal radiation
Thermal radiation is the process by which bodies emit energy in the form of electromagnetic waves due to their temperature. This phenomenon can be understood in terms of key concepts and physical laws that explain how radiation is emitted, absorbed and reflected based on the properties of the materials and their temperature.
black body radiation
A black body is a theoretical object that absorbs all the radiation that falls on it without reflecting or transmitting it. This depends only on its temperature and is considered the ideal model to understand the emission of thermal radiation. The radiation spectrum of a black body describes the distribution of energy at different wavelengths, showing how bodies emit more radiation at shorter wavelengths as their temperature increases.
Stefan-Boltzmann law
It states that the total power radiated per unit area of a black body is proportional to the fourth power of its absolute temperature. The Stefan-Boltzmann constant, a fundamental value in this law, quantifies this relationship and allows us to calculate the amount of energy emitted by a body based on its temperature.
Wien's Law
Wien's Shift Law describes how the peak wavelength of the radiation emitted by a blackbody shifts toward shorter wavelengths as the temperature increases. It helps predict where in the electromagnetic spectrum most radiation is emitted, whether in the visible, infrared, or even ultraviolet spectrum.
Planck's Law
It provides a precise formula for the intensity of radiation at each wavelength, explaining how radiation is distributed in the electromagnetic spectrum for a given temperature.
Emissivity, reflectivity and radiation absorption
They are coefficients that characterize how materials interact with thermal radiation. Emissivity is the ability of an object to emit radiation compared to an ideal blackbody; Absorption (or absorptivity ) measures how much radiation the object absorbs; and reflectivity indicates how much radiation is reflected from its surface. Materials with high emissivity and low reflectivity approximate black body behavior.
Boltzmann and Stefan-Boltzmann constants
The Boltzmann constant is fundamental in physics: it relates the temperature of a system to its thermal energy. The Stefan-Boltzmann constant is specific to thermal radiation, quantifying the power radiated by a black body as a function of its temperature.
Visible and ultraviolet (UV) radiation
The thermal radiation of bodies, depending on their temperature, can cover different ranges of the electromagnetic spectrum. At very high temperatures, bodies can emit radiation in the visible spectrum or even in the ultraviolet, as is the case with stars. Visible and ultraviolet radiation are examples of electromagnetic radiation with different wavelengths and energies, and are considered types of non-ionizing radiation when they are at energy levels that do not cause ionization in atoms.
Gray body
In contrast to an ideal black body, a gray body is one that does not absorb all of the incident radiation but still emits thermal radiation in proportion to its temperature. The emissivity of a gray body is constant and lower than that of a black body, which makes it a more realistic model to describe the radiation of real materials.
The human body emits infrared radiation, a result of metabolic processes and thermal properties of the skin.
Heat and thermal energy transfer
Heat transfer is the process by which thermal energy moves from one region to another of lower temperature, and can occur through several basic mechanisms. These phenomena are fundamental to understanding how thermal energy is distributed and conserved in different media and environments.
heat transfer
It describes the movement of thermal energy from one region or material to another, and can occur through three main mechanisms: conduction, convection, and radiation . Heat transfer is fundamental in the thermal regulation of physical, biological and industrial systems.
Thermal conduction
Conduction is the mechanism by which heat is transferred directly through a solid material or between two or more that are in physical contact. Heat flows due to the movement of particles at the molecular level, and the amount of heat transferred depends on the material's thermal conductivity, temperature gradient, and contact area.
Thermal convection
It is the process of heat transfer in fluids (liquids or gases) and occurs due to the movement of the molecules of the fluid. This phenomenon can be natural , when the movement of the fluid is induced by differences in temperature and density, or forced , when an external mechanism such as a fan or pump is used to move the fluid.
Empty space and thermal radiation
In empty space, where there is no matter to conduct or transport heat, energy transfer occurs solely through thermal radiation. This is important in the context of outer space and in applications where material contact is minimized to reduce unwanted heat transfer.
Heat propagation and radiant flux
The spread of heat is its movement through different media; The concept of radiant flux refers specifically to the transfer of thermal energy using electromagnetic waves. Radiant flux is measured in terms of radiant intensity , which is the amount of energy emitted per unit area in a specific direction.
Radiant intensity and flux density
Radiant intensity refers to the amount of radiant energy emitted or received per unit area, while flux density describes the flow of radiant energy passing through a given area. These measurements are key to analyzing how thermal radiation is distributed in different materials and environments.
Radiative balance
Radiative balance is achieved when the amount of thermal energy that a body or system emits is equal to what it absorbs, thus achieving a stable state in terms of its temperature. This concept is important in closed systems and in the thermodynamics of celestial bodies, where balance is achieved naturally with their environment.
Specific heat and heat capacity
Specific heat is the amount of energy required to raise the temperature of a unit mass of a material by one degree Celsius, while heat capacity is the total amount of heat required to raise the temperature of an entire object. Both concepts are essential to understand how different materials respond to heat transfer and to calculate thermal energy in heating and cooling processes.
Latent heat
It is the energy absorbed or released by a substance during a phase change, such as fusion, without changing its temperature. It is essential in processes of change of state and in phenomena such as evaporation and condensation, where the transfer of energy is not directly reflected in the variation in temperature.