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Work in a PV curve

  1. Dec 26, 2011 #1
    Hey all,

    In one of my textbooks, there is a passage in the thermodynamics section that states that:

    For a closed cycle where the system returns to its initial state, the work done is the area enclosed by the curve (when looking at a Pressure-Volume graph).

    Shouldn't the work done by this process be a total of 0 instead???

    Thanks in advance.
     
  2. jcsd
  3. Dec 26, 2011 #2

    cjl

    User Avatar

    Not necessarily. A closed cycle can do work. Suppose it cycles between two states. If the work done getting from state 1 to state 2 is much larger than the work done (with the opposite sign of course) from state 2 back to state 1, the cycle will do net work. Note that this does require the system to be under a different load during different parts of the cycle. This changing load is what allows the system to end at the same state that it started while still doing work.
     
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