In 1900, Max Planck proposed the quantum theory to explain the emission and absorption of radiations. Heated objects give off these radiations. According to his revolutionary hypothesis, energy travels in a discontinuous manner and is composed of a large number of tiny discrete units called quanta.

**Main postulates of Plank’s Quantum Theory:**

The main points of the theory are:

1. Energy is not emitted or absorbed continuously. Each wave packet or quantum is associated with a definite amount of energy. In the case of light, the quantum of energy is often called the photon.

2. The amount of energy associated with a quantum of radiation is proportional to the frequency of the radiation.

Ε ∝ ∨

E=h∨

Where ‘h’ is a constant known as Planck’s constant and it is equal to 6.625X10^{-34} Joule sec.

3. A body can emit or absorb energy only in terms of integral multiples of a quantum.

E = n h ∨

Where

n= 1, 2, 3… (Integral Multiple)

The frequency ‘∨’ is related to the wavelength ‘λ’ of the photon as.

∨ = c/λ.

E = h c/λ