Black body: An ideal body, which emits and absorbs all frequencies, is called a black body. The radiation emitted by such a body is called black body radiation.

Planck’s Quantum Theory

Planck said that atoms and molecules could emit (or absorb) energy only in discrete quantities and not in a continuous manner, a belief popular at that time.

Planck gave the name quantum to the smallest quantity of energy that can be emitted or absorbed in the form of electromagnetic radiation.

E µ n    Þ  E = hn Þ

The proportionality constant, ’h’ is known as Planck’s constant and has the value 6.626 10-34 Js.