# Equilibrium temperature of a black body when the volume of the black body is changed

If a black-body is at an equilibrium temperature T of a certain volume. If we increase size of blackbody does the equilibrium temperature of the blackbody will change?

## 1 Answer

The internal energy per unit mass (the specific internal energy) of a solid is proportional to temperature. The total internal energy equals the internal energy per unit mass times the total mass. Increasing the volume (and thus the mass) of the a solid, in the absence of any heat transfer from the surroundings to the solid, or a black body that generates energy (sum), decreases the internal energy per unit mass. That mean the temperature should decrease. This would apply to any solid, not just a blackbody.

Hope this helps.

• That means you want to say that when the internal energy of a body is used to increase the temperature of itself, as a result the temperature of a body will decrease. – no one Aug 31 '19 at 17:10
• @Bikash Kumar Das what I am saying is if the amount of internal energy is fixed and you just increase the volume the energy density goes down and so does the temperature. – Bob D Aug 31 '19 at 18:58