EasyPhysicsHigh School (11–12)Heat & Thermodynamics › Heat Engines, the Second Law and EntropyNumericalBoard ExamAPIB
A gas goes round a rectangle on a pressure-volume graph…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A gas goes round a rectangle on a pressure-volume graph. The bottom side is at and the top at ; the volume goes from to litres. Find the net work and the net heat when the loop is traced (a) clockwise and (b) anticlockwise.
Need a reminder? The key ideaShow
In a cycle the gas returns to its start, so and the net heat equals the net work. The net work is the area of the loop on a pressure-volume graph: positive for a clockwise loop, negative for an anticlockwise one.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Area. .
Step 2. Clockwise. The gas expands at the high pressure and is squeezed at the low one: .
Step 3. Anticlockwise. The other way round: ; the gas gives out of net heat.
Answer: (a) each; (b) each.
Check. Clockwise: out at the top, in at the bottom.
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