Stefan’s constant

The Stefan-Boltzmann Law and Wien s Law for black body radiation have been unified into Planck s Law for black body radiation, from which Planck s constant was first introduced. Planck s analysis of the spectral distribution of black body radiation led him to an understanding of the quantisation of energy and radiation and the role of the photon in the theory of radiation. The precise law relates the intensity of the radiation at all wavelengths with the temperature and has the form ... 

Two large parallel plates with grey surfaces are situated 75 mm apart one has an emissivity of 0.8 and is at a temperature of 350 K and the other has an emissivity of 0.4 and is at a temperature of 300 K. Calculate the net rate of heat exchange by radiation per square metre taking the Stefan-Boltzmann constant as 5.67 x 10-8 W/m2 K4. Any formula (other than Stefan s law) which you use must be proved. 

If 1 jvg is neglected in comparison with 1 jvi, the law of rectilinear diameter of Cailletet and Mathias ( 5.VIIB) gives llvi=A—BTy where A and B are constants, and r=abs. temp. Hence, from Bakker s equation ( 4.VIIIL), l. =alvi, it foUows that l —a A—BT), where a is van der Waals s constant. From Stefan s equation ( 6.VIII G),... 

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