A black body is a system that absorbs all the radiation that falls on it. For instance, a matte black body surface or a large cavity with a small hole in its wall is a black body and emits black body radiation.
In 1859, G.R Kirchhoff verified that the ratio so the emissive power to the absorptivity at a given temperature T is the same for all bodies, irrespective of the material of which the body is made.
In 1900, Lord Rayleigh proposed a new black body radiation law which was later modified by J. Jeans in 1905 and is now known as the Rayleigh-Jeans formula.
In his investigation, to find a relation between the radiation emitted by a black body as a function of temperature and wavelength, Max Planck (1858-1947) developed the now famous equation named after him.
He reported his findings, which were based on his experimental work on October 19, 1900. Planck's law describes the electromagnetic radiation emitted by a black body in thermal equilibrium at a definite temperature. It describes the distribution of energy radiated by a black body. It is a pioneering result of modern physics and quantum theory.
His efforts laid the foundation of the quantum theory, for which he received the Nobel Prize in 1918.
Planck's law of black-body radiation
