Question
A body of surface area A and emissivity e is heated to a temperature T and placed in an enclosure maintained at temperature T0 (T0<T). Find the net rate of loss of heat by the body by radiation.
Solution
According to Stefan’s law, at temperature T, the energy emitted per second per unit area by black body is,

Therefore heat energy emitted by any body at temperature T per second is given by,
According to Prevost’s theory, due to temperature of enclosure, body absorbs the thermal radiation.
Therefore, due to temperature T0 of enclosures, the heat energy absorbed by body per second is,

Net heat lost by body at T placed in enclosure at temperature T is,
Negative sign mplies heat lost by the body.

Therefore heat energy emitted by any body at temperature T per second is given by,

According to Prevost’s theory, due to temperature of enclosure, body absorbs the thermal radiation.
Therefore, due to temperature T0 of enclosures, the heat energy absorbed by body per second is,

Net heat lost by body at T placed in enclosure at temperature T is,


Negative sign mplies heat lost by the body.