A historic failure of classical physics is its description of the electro- magnetic radiation from a black body. Consider a simple model for an ideal black body consisting of a cubic cavity of side L with a small hole in one side. (a) Assuming the classical equipartition of energy, derive an expression for the average energy per unit volume and unit frequency range (Rayleigh- Jeans' Law). In what way does this result deviate from actual observation? 0 Fig. 2.16. (b) Repeat the calculation, now using quantum ideas, to obtain an expression that properly accounts for the observed spectral distribution (Planck's Law). (c) Find the temperature dependence of the total power emitted from the hole.

A historic failure of classical physics is its description of the electro- magnetic radiation from a black body. Consider a simple model for an ideal black body consisting of a cubic cavity of side L with a small hole in one side. (a) Assuming the classical equipartition of energy, derive an expression for the average energy per unit volume and unit frequency range (Rayleigh- Jeans' Law). In what way does this result deviate from actual observation? 0 Fig. 2.16. (b) Repeat the calculation, now using quantum ideas, to obtain an expression that properly accounts for the observed spectral distribution (Planck's Law). (c) Find the temperature dependence of the total power emitted from the hole.