In a cyclic process, after one complete cycle the internal energy of the system
- A. increases by the work done
- B. decreases by the heat rejected
- C. returns to its original value, so the net heat supplied equals the net work done
- D. becomes zero
Explanation
Internal energy is a function of state, so returning to the same pressure, volume and temperature restores it exactly, and the first law then reduces to net heat equals net work. That work is the area enclosed by the loop on a pressure volume diagram. Every heat engine relies on this, since it must return to its starting state to run continuously.