Characteristics of blackbody radiation spectrum :

1. The emissive power R_λ for every wavelength λ increases with increasing temperature.

2. Each curve has a characteristic form with a maximum for R_λ at a certain wavelength λ_m .

3. λ_m depends on the absolute temperature of the body and, with increasing temperature, shifts towards shorter wavelengths, i.e., towards the ultraviolet end of the spectrum.

4. λ_mT = a constant.

5. The area under each curve gives the total radiant power per unit area of a blackbody at that temperature and is proportional to T⁴ , (Stefan-Boltzmann law)

Notes :

1. Experimental work on the distribution of energy in blackbody radiation, was carried out by German physicists Otto Lummer (1860-1925), Wilhelm Wien (1864-1928) and Ernst Pringsheim (1859-1917).

2. Explanation of the radiation spectrum, given by Wien on the basis of thermodynamics could account only for the short wavelength region. The formula obtained by Rayleigh and Jeans, on the basis of the equipartition of energy could account only for long wavelength region. Planck’s empirical formula, put forward in 1900, could account for the entire spectrum.