Radiation

Radiant heat transfer, or radiation, is the rapid transfer of heat through space from a warmer object to the surface of a cooler one. Once molecules on the surface of an object absorb heat rays, they vibrate rapidly. The vibration generates frictional heat within the object. At no time does the radiating body come into direct contact with the object, yet heat energy is transferred from one to the other. Because there is no direct contact, radiation is sometimes described as a form of indirect heat. Examples of appliances that heat primarily by radiation include toasters, broilers, infrared heat lamps, and conventional ovens.