The first law of thermodynamics states that the heat supplied to a system equals
- A. the work done by the system alone
- B. the increase in internal energy plus the work done by the system
- C. the fall in internal energy
- D. the temperature rise multiplied by the mass
Explanation
The law is conservation of energy applied to heat: energy entering as heat either raises the internal energy or leaves again as work done on the surroundings. Sign conventions matter, since heat supplied to the system and work done by the system are both counted as positive. A machine that produced work with no energy input would violate this law.