Planck’s law of radiation The spectral energy distribution from a black body , at a given temperature, has a unique form as shown in the fig. p4. Max Planck in 1900, obtained the correct form of this distribution which is known as Planck’s law. Planck abandoned the hypothesis that radiation can be absorbed or emitted continuously, but instead assumed that it can only happen in discrete steps. The Planck’s radiation law is given as,
En dn = 8p V h c-3 n 3 [exp(h n /(kT)) -1]-1 dn
where En dn is the amount of energy between frequency range n and n +dn , V the volume of the cavity, c the velocity of light, k the Boltzmann constant, T the absolute temperature and h the Planck’s constant. The Planck’s investigation on the black body radiation led to the quantum theory of radiation.