It is the process by which heat is transmitted from one place to another without heating the intervening medium. The heat from the sun reaches the earth by the process of radiation after traveling through millions of kilometers of vacuum. Due to absence of any material medium, the transmission of heat by conduction and convection is not possible. Just as light, heat radiation can pass through vacuum.
Radiation:
It is the process by which heat is transmitted from one place to another without heating the intervening medium. The heat from the sun reaches the earth by the process of radiation after traveling through millions of kilometers of vacuum. Due to absence of any material medium, the transmission of heat by conduction and convection is not possible. Just as light, heat radiation can pass through vacuum.
Thermal radiation is defined as the energy emitted by a body in the form of radiation on account of its temperature.
ADVERTISEMENTS:
All objects emit thermal radiation continuously. The energy and wavelength of the thermal radiation depends on the temperature and the nature of the hot radiating body.
Black Body:
A perfect black body is one which absorbs heat radiation of all the wavelengths, which fall on it. Such a body neither reflects nor transmits any part of the incident heat radiation and hence appears black. Thus the absorption of a perfect black body is unity.
A perfect black body when heated emits radiation on all possible wavelengths at that temperature. The wavelength range of emitted radiation is independent of the material of the body and depends only on the temperature of the black body.