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Homework Help: Entropy and Maximum work for two idential, finite sized bodies

  1. Nov 6, 2011 #1
    Two idential, finite sized bodies of constant volume and constant heat capacity are used to drive a heat engine- heat is taken from the hot (Th) body, work is done, and heat is ejected to the cold (Tc) body. Both bodies wind up at Tf

    (a) What is the change in the entropy of the system?

    (b) What is the maximum amount of work that can be done?

    Relevant equations
    Cv is not time dependent

    (a) I got ΔS=nCv*ln(Th/Tc)
    (b) No idea where to start, any help would be great!
  2. jcsd
  3. Nov 8, 2011 #2

    I like Serena

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    Homework Helper

    Welcome to PF, J.Welder12! :smile:

    For (a) you need to consider the 2 bodies separately and apply your formula ΔS=nCv*ln(T2/T1) to them.
    This gives 2 contributions to ΔS.

    For (b) you should calculate U for both bodies before and after.
    The difference is the maximum amount of work that can be extracted.
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