Heat Transfer

Thermal energy is transferred only when there is a difference in the temperature and it always flows from a region of higher temperature to a region of lower temperature.

When two objects are at same temperature, they are in thermal equilibrium. This means there is no net heat transfer between them.

Note
  • No net heat transfer ≠ no heat transfer
Reason: 
When we say there is no net heat transfer between two objects, A and B, actually there is still heat transfer between them. It is so because the amount of heat transfer from A to B is same as that amount transferred from B to A. Thus, no net heat transferred between A and B. This means at thermal equilibrium, there is still heat transfer between two objects but no net heat transfer between them.
  • A is in thermal equilibrium with B and B is in thermal equilibrium with C, then A, B and C are all in thermal equilibrium.

Thermal energy is transferred by three processes:
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