Question

How did plank explain the black body radiation?

Answer 1

Planck's Law of Radiation:

1. A blackbody is defined as a body that absorbs all the radiant energy falling on it so that its absorptive power is unity.
2. The failure of the Rayleigh-Jeans formula to explain the observed energy distribution law of blackbody radiation showed that there was something wrong either with the equation law or with the classical electromagnetic theory, or with both.
3. Max Planck examined these flaws and put forward a new postulate regarding the nature of vibration of the linear harmonic oscillators which are in equilibrium with the electromagnetic radiation within the cavity.
4. A linear harmonic oscillator is defined as a body when displaced from its mean position experiences a force that is proportional to the displacement of the body and in the direction of its mean position.
5. According to Planck, an oscillator can have a discrete set of energies that are integral multiples of a finite quantum of energy ${\epsilon }_0=h\nu$ where $h$ is a constant known as Planck's constant and $\nu$ is the frequency of the oscillator.
6. Thus the energy of the oscillator can only have the values ${\epsilon }_0=n{\epsilon }_0=nh\nu$, where $n$ is an integer or zero.
7. Obviously, the ground state energy of the oscillator will be zero.
8. Planck also hypothesized that the energy change of the oscillator due to the emission or absorption of radiation can also occur in a discrete quantity $h\nu$.
9. Planck estimated the value of $h$ by fitting his theory to the experimental data.
10. Planck's constant $h$ is a universal constant and plays a crucial role in all quantum phenomena.
11. Its value is $h=6.626\times {10}^{-34}Js$.