What is a black body?
A body which absorbs all the radiations falling at its surface is called a black body. A black body is also a perfect emitter .i.e. emits maximum energy out of all the bodies at same temperature.
Whenever a body gets hot, it starts emitting radiation. Max Planck gave his quantum theory of radiation to explain the distribution of energy in the spectrum observed when a hot body emits heat radiations. The energy per unit area of the body i.e. the energy density depends upon the temperature of the hot body. Also the radiations of a hot body at a particular temperature are not of single frequency or wavelength but contain many wavelengths.
The following are the characteristics of the curves observed:-
a) For every temperature, there is a wavelength for which the energy density is maximum i.e. the energy emitted is maximum.
b) The wavelength at which the body emits maximum energy decreases with increase in temperature of the hot body.
c) Higher the temperature of the hot body, higher is the maximum energy density.
