Radiation is created by the motion of charged particles. All matter with a temperature greater than absolute zero will emit radiation. The movement of charges will produce electromagnetic radiation. There is a wide range of radiation which reflects the wide range of energies and accelerations of the charges in any piece of matter at a single temperature.
Some examples of thermal radiation are visible light and infrared light emitted by an incandescent light bulb, the infrared radiation emitted by animals and detectable with an infrared camera, and the cosmic microwave background radiation.
There are four main properties of thermal radiation
- Thermal radiation emitted by a body at any temperature consists of a number of frequencies.
- The dominant frequency range of the emitted radiation shifts to high frequencies as the temperature of the emitter increases.
- The total amount of radiation of all frequencies increase steeply as the temperature rises. It gros as T4, where T is the absolute temperature of the body.
- The rate of electromagnetic radiation emitted at a given frequency is proportional to the amount of absorption that would be experience by the source.