Describe briefly Planck's Quantum Theory.

This theory can be simply stated as:
(i) Radiation is associated with energy.
(ii) Radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy.
(iii) Each packet of energy is associated with a definite amount of energy and is known as quantum. In the case of light, the ‘quantum’ is known as ‘photon’.
(iv) The magnitude of quantum is directly proportional to the frequency of radiation.
    E ∝ v
i.e. E = hv
where v = Frequency of radiation
h = Planck’s constant
= 6.625 x 10^-34Js
(or 6.625 X 10^-34 kg m² s^-1)
= 3.99 x 10^-13 k Js mol^-1

(v) A body can radiate or absorb energy in whole number multiples of a quantum i.e. nhv, where n = 1,2,3,4......etc.