EasyPhysicsHigh School (11–12)Heat & Thermodynamics › Laws of ThermodynamicsConceptualBoard ExamAPA-LevelIB
A gas takes in 210 J of heat. At the same time a piston does 75 J of work on it…
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 takes in of heat. At the same time a piston does of work on it. Give the signs of and in our convention, and find . Does an ideal gas get warmer or cooler?
Need a reminder? The key ideaShow
The first law: . is positive when heat goes into the gas; is positive when the gas does work on its surroundings, so work done on the gas is negative. For an ideal gas, means it gets warmer.
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. Signs. Heat goes in: . Work is done on the gas: .
Step 2. First law. .
Answer: , , : it gets warmer.
Check. Both the heat and the work add energy, so must be larger than either.
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