Math 2.0

Classical thermodynamics, heat transfer Definition

Thermal radiation

Builds on Electromagnetic radiationThermodynamic temperatureInternal energy

Definition

Let a body of matter have absolute temperature T>0T > 0. Thermal radiation is the electromagnetic radiation that the body emits as a result of the thermal motion of its charged particles. It is produced at the expense of the internal energy of the body. Its spectrum and power depend on the temperature and on the material and surface of the body.

Remarks

Example: the Sun, whose surface is at about 58005800 K, emits thermal radiation with most of its power in the visible and near infrared. A body at room temperature emits thermal radiation mainly at wavelengths around 1010 micrometres.

Non-example: the radio waves sent by an antenna. They are produced by an electric current driven by a transmitter, not by thermal motion, so they are not thermal radiation, even though they are electromagnetic. The light of a laser is likewise not thermal.

In heat transfer, the range of wavelengths that matters is roughly from 0.10.1 to 100100 micrometres.

Reading path

To understand this page from the ground up, read these 4 pages in order. The foundations come first.

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Electromagnetic radiation, concept, no evidence levelElectromagnetic radia…conceptInternal energy, concept, no evidence levelInternal energyconceptThermodynamic temperature, concept, no evidence levelThermodynamic tempera…conceptThermal radiation, definition, no evidence levelThermal radiationdefinition
Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
  • no evidence level
  1. Electromagnetic radiation concept
  2. Internal energy concept
  3. Thermodynamic temperature concept
  4. Thermal radiation definition

Further reading

  1. Web https://en.wikipedia.org/wiki/Thermal_radiation
About this page
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Kinddefinition
WritingW0 stub
MSC80A21, 78A40
DefinesThermal radiation
UsesElectromagnetic radiation, Thermodynamic temperature, Internal energy
Changed3 November 2026

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