Heat and Thermodynamics

12.7 Thermodynamics of Radiation

We have proved that radiation inside an enclosure at a uniform temperature can be regarded as a perfect gas. Accordingly, radiation should obey the laws of perfect gas.

Let V be the total volume of the enclosure and u the energy density inside the enclosure. Then, total energy in the enclosure is

 

U = V u

 

But,

 

u = aT⁴

 

∴          U = VaT⁴            (12.29)

 

This gives

 

 

Again,

 

 

This gives