Max Plank in 1901 , gave a new revolutionary theory known as Quantum theory of radiation.
Main features of this theory are :
1. Radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy called Quanta.
Each quanta is associated with a definite amount of energy.
2. E is directly proportional to frequency of light,
E=hv where h is known as planks constant. h= 6.63x10-34 Js
3. The total amount of energy emitted or absorbed by the body will be some whole no. multiple of quantum,
i.e, E=nhv , where n is an integer such as 1, 2, 3, ....
Since, the frequency ν, wavelength λ, and speed of light c are related by λν = c, the Planck relation for a photon can also be expressed as
The above equation leads to another relationship involving the Planck constant.