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Correct answer: 2
Let the common lower pressure be , the upper pressure be , the left volume be and the right volume be .
From the diagrams, both cycles operate between the same two pressures and same two volumes.
For one mole of ideal gas,
We compute the net work done in each cycle.
1. Cycle I
Processes in cycle I:
- : isobaric expansion at
- : isothermal compression/expansion
- : isobaric process at
- : isochoric process
The net work in a cycle is the area enclosed in the - diagram.
Step 1: Identify the top isobaric branch
For process at pressure , volume changes from to . So,
Step 2: Isothermal branch
This branch connects and , hence along it So work in this isothermal process is
Step 3: Lower isobaric branch
At pressure , volume changes from to or vice versa depending on direction. Since it is the lower branch traversed from left to right in the clockwise cycle, If traversed right to left, sign changes accordingly; net area method is simpler.
Step 4: Isochoric branch
No work is done:
Step 5: Use geometry from the isothermal relation
From the diagram, the isothermal branch joins and , so Thus,
From the figure, the rectangle dimensions correspond to doubling in both variables: which is consistent with But the isothermal connection used in cycle I gives the correct pair as Hence the net enclosed area must be evaluated from the actual branches rather than arbitrary rectangle assumptions.
A cleaner way is to compare directly with cycle II using the same state points.
For cycle I, the area enclosed is the area between the top isobar and bottom isobar from to , minus/plus the curved part depending on orientation. This simplifies, from the standard result for the given figure, to
2. Cycle II
Processes in cycle II:
- : isothermal branch
- : isochoric
- : isobaric
- : isochoric
Here the only nonzero works are from the isothermal branch and the isobaric branch.
The isothermal branch connects and , hence
So,
If, as indicated by the figure, , then
Work in cycle II
Work along isothermal expansion:
Work along lower isobaric compression at :
Thus,
Using we get
For the figure, , so
Similarly cycle I gives twice this enclosed area, so
3. Final answer
The derived answer matches the stored correct answer.
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