Consider a Carnot cycle starting at the state of highest pressure and smallest volume.Call the isothermal expansion from this state step 1,the adiabatic expansion which follows step 2,the isothermal compression that then follows step 3,and the adiabatic compression which returns the system to the initial state step 4.In which steps does the internal energy of the system increase?
A)1 and 2
B)3 and 4
C)1 and 3
D)2 and 4

Question

Quizplus · Accepted Answer

During an isothermal expansion, the internal energy of the system increases as heat flows into the system. During an adiabatic expansion, however, there is no heat transfer and therefore no increase in internal energy. Similarly, during an isothermal compression, heat leaves the system and the internal energy decreases. Finally, during an adiabatic compression, there is no heat transfer and no change in internal energy.

So, in the Carnot cycle described, the internal energy increases during steps 3 and 4, when heat is leaving the system during the isothermal compression and the subsequent adiabatic compression. The internal energy does not increase during steps 1 and 2, because there is heat flowing into the system during the isothermal expansion, but no increase in internal energy during the adiabatic expansion. Therefore, the correct answer is option B.

Consider a Carnot Cycle Starting at the State of Highest