EasyPhysicsHigh School (11–12)Heat & Thermodynamics › Laws of ThermodynamicsNumericalBoard ExamAPA-LevelIB
Find Δ U for a gas in each case, and say whether it gets warmer or cooler…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Find for a gas in each case, and say whether it gets 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. (a) : warmer.
Step 2. (b) : cooler. It loses heat and does work.
Step 3. (c) : warmer, squeezed with no heat out.
Step 4. (d) : warmer, heated in a rigid tank.
Answer: (a) , (b) , (c) , (d) .
Watch out. Subtracting a negative adds it.
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