JEE Main & Advanced Physics Transmission of Heat Law of Distribution of Energy (Plank's Hypothesis)

(1) The theoretical explanation of black body radiation was done by Planck.

(2) According to Plank's atoms of the walls of a uniform temperature enclosure behave as oscillators, each with a characteristic frequency of oscillation.

(3) These oscillations emits electromagnetic radiations in the form of photons (The radiation coming out from a small hole in the enclosure are called black body radiation). The energy of each photon is hn. Where n  is the frequency of oscillator and h is the Plank's constant. Thus emitted energies may be hn, 2hn, 3hn ... nhn but not in between.

According to Planck's law \[{{E}_{\lambda }}d\lambda =\frac{8\pi hc}{{{\lambda }^{5}}}\,\frac{1}{[{{e}^{hc/\lambda KT}}-1]}\,d\lambda \]

where c = speed of light and k = Boltzmann's constant. This equation is known as Plank's radiation law. It is correct and complete law of radiation

(4) This law is valid for radiations of all wavelengths ranging from zero to infinite.

(5) For radiations of short wavelength \[\left( \lambda <<\frac{hc}{KT} \right)\] Planck's law reduces to Wien's energy distribution law \[{{E}_{\lambda }}d\lambda =\frac{A}{{{\lambda }^{5}}}{{e}^{-\,B/\lambda T}}d\lambda \]

(6) For radiations of long wavelength \[\left( \lambda >>\frac{hc}{KT} \right)\] Planck's law reduces to Rayleigh-Jeans energy distribution law \[{{E}_{\lambda }}d\lambda =\frac{8\pi KT}{{{\lambda }^{4}}}d\lambda \]