What is Thermal radiation?
'''Thermal radiation''' is [[radiation]] that things make because they are warm. It may be felt as [[heat]] or seen as [[light]].<ref>Robert Siegel, ''Thermal Radiation Heat Transfer'', Fourth Edition (London; New York: Taylor & Francis, 2002), p. 1</ref> It is a form of [[heat transfer]] that is moved from one place to another by [[electromagnetic radiation|electromagnetic radiation waves or rays]]. It does not require a form of [[matter]] to be transferred. Any matter which is at any temperature above absolute zero (0 K or -273°C) gives out and absorbs thermal radiation. Like [[light]], thermal radiation travels through vacuum at a speed of approximately 3X10^8 metres per second. Thermal radiation can also travel in all directions. Dark, dull surfaces give out more thermal radiation while bright and shiny surfaces give out comparatively less thermal radiation. Those surfaces which give out thermal radiation well also absorb thermal radiation well. For example a [[person]] in front of a [[fire]] can warm up because of the light of the fire, even if the air is cold.<ref>Mahesh M. Rathore; Raul Raymond Kapuno, ''Engineering Heat Transfer'' (Sudbury, MA: Jones & Bartlett Learning, 2011), p. 807</ref> Another example of thermal radiation is the heat that comes from the [[Sun]] to the [[Earth]]. Warmer things make more radiation, and the electromagnetic waves are shorter. Most things on Earth are warm enough to make [[infrared]] radiation. [[Incandescent light bulb]]s are so hot, their radiation includes [[visible light]]. ==Related pages== * [[Heat transfer]] * [[Heat conduction]] * [[Convection]] == References == {{reflist}} {{physics-stub}} [[Category:Thermodynamics]] [[Category:Heat transfer]]