Thermal radiation

Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. Thermal radiation transmits as an electromagnetic wave through both matter and vacuum. When matter absorbs thermal radiation its temperature will tend to rise. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electronic, molecular, and lattice oscillations in a material.^[1] Kinetic energy is converted to electromagnetism due to charge-acceleration or dipole oscillation. At room temperature, most of the emission is in the infrared (IR) spectrum.^[2]^: 73–86 Thermal radiation is one of the fundamental mechanisms of heat transfer, along with conduction and convection.

The primary method by which the Sun transfers heat to the Earth is thermal radiation. This energy is partially absorbed and scattered in the atmosphere, the latter process being the reason why the sky is visibly blue.^[3] Much of the Sun's radiation transmits through the atmosphere to the surface where it is either absorbed or reflected.

Thermal radiation can be used to detect objects or phenomena normally invisible to the human eye. Thermographic cameras create an image by sensing infrared radiation. These images can represent the temperature gradient of a scene and are commonly used to locate objects at a higher temperature than their surroundings. In a dark environment where visible light is at low levels, infrared images can be used to locate animals or people due to their body temperature. Cosmic microwave background radiation is another example of thermal radiation.

Blackbody radiation is a concept used to analyze thermal radiation in idealized systems. This model applies if a radiation object meets the physical characteristics of a black body in thermodynamic equilibrium.^[4]^: 278 Planck's law describes the spectrum of blackbody radiation, and relates the radiative heat flux from a body to its temperature. Wien's displacement law determines the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the radiant intensity.^[4]^: 280 Where blackbody radiation is not an accurate approximation, emission and absorption can be modeled using quantum electrodynamics (QED).^[1]

^ ^a ^b Howell, John R.; Mengüç, M. Pinar; Siegel, Robert (2016). Thermal radiation heat transfer (Sixth ed.). Boca Raton, Fla. London New York: CRC Press, Taylor & Francis Group. ISBN 978-1-4665-9326-8.
^ Cite error: The named reference :1 was invoked but never defined (see the help page).
^ Cite error: The named reference :3 was invoked but never defined (see the help page).
^ ^a ^b Huang, Kerson (1987). Statistical mechanics (2nd ed.). New York: Wiley. ISBN 978-0-471-81518-1.

[:9-1] Howell, John R.; Mengüç, M. Pinar; Siegel, Robert (2016). Thermal radiation heat transfer (Sixth ed.). Boca Raton, Fla. London New York: CRC Press, Taylor & Francis Group. ISBN 978-1-4665-9326-8.

[:1-2] Cite error: The named reference :1 was invoked but never defined (see the help page).

[:3-3] Cite error: The named reference :3 was invoked but never defined (see the help page).

[:8-4] Huang, Kerson (1987). Statistical mechanics (2nd ed.). New York: Wiley. ISBN 978-0-471-81518-1.

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