Practice question · Select all that apply
Which statements about cyclic processes are correct?
Hints
- Three follow from U being a state function and from the P-V diagram; one contradicts the second law.
- Even a perfect engine must reject heat.
Show the answer
- A. The net work equals the difference between heat absorbed and heat rejected
- C. The internal energy change over a complete cycle is zero
- D. The net work is the area enclosed by the cycle on a P-V diagram
Why
Returning to the same state makes , so the net work is the difference of the heats, and it appears as the enclosed area. Full conversion is forbidden by the second law regardless of friction.
Practise Cyclic Processes and the Carnot Cycle
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