A thermodynamic system goes from state A to B along path ACB and is brought back to A along path BDA in the P–V diagram. The net work done during the complete cycle is given by the area:
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A thermodynamic system goes from state A to B along path ACB and is brought back to A along path BDA in the P–V diagram. The net work done during the complete cycle is given by the area:

G1 Physics · Accepted Answer

Step 1: The work done over a path in the P–V diagram is the signed area under the path, W = ∫P dV. Step 2: During A→C→B (expansion), the work is the positive area below the upper curve ACB. Step 3: During B→D→A (compression), work is negative and equals minus the area below the lower return curve BDA. Step 4: Subtracting the two areas leaves exactly the area enclosed between curves ACB and BDA. Step 5: The enclosed loop is labelled A→C→B→D→A, i.e. ACBDA. Final answer: (C) area ACBDA.