Explain the phenomenon of black body radiation.

(N/A) The first concrete explanation for the phenomenon of black body radiation was given by Max Planck in $1900$.
When solids are heated,they emit radiation over a wide range of wavelengths.
Example: When an iron rod is heated in a furnace,it first turns dull red and then progressively becomes more and more red as the temperature increases; the colour and frequency change.
Black body: An ideal body,which emits and absorbs radiations of all frequencies,is called a black body,and the radiation emitted by such a body is called black body radiation.
The exact frequency distribution of the emitted radiation: At a given temperature,the intensity of radiation emitted increases with a decrease in wavelength,reaches a maximum value at a given wavelength,and then starts decreasing with a further decrease in wavelength (see the figure).
Black body radiation cannot be explained by classical electromagnetic radiation theory but is explained by Planck's quantum theory.