Stefan-Boltzmann Law

Stefan-Boltzmann law of radiation:

According to this law the rate of emission of radiant energy per unit area or the power radiated per unit area of a perfect blackbody is directly proportional to the fourth power of its absolute temperature.

Thus, the power radiated by a perfect blackbody depends only on its temperature and not on any other characteristics such as colour, materials, nature of surface etc. It is written as,

If the perfect blackbody having absolute temperature T is kept in a surrounding which is at a lower absolute temperature T0 , then 

Since the loss or gain of energy per unit area per unit time is proportional to the fourth power of absolute temperature, this law is very significant in deciding the thermal equilibrium of physical systems. If the absolute temperature of a body is doubled, the power radiated will increase by a factor of 24 = 16. Or if a body radiates with some rate at room temperature (300 K), the rate will double even if we increase the temperature of the body by 57 ºC.