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Thermal efficiency of engine

  1. Dec 12, 2016 #1
    1. The problem statement, all variables and given/known data
    http://i.imgur.com/SQ6jx94.png
    SQ6jx94.png
    (sorry for the low resolution~ it's already the best i can make it~)

    2. Relevant equations
    U=Q+W
    the three variables of isobaric, isochoric, adiabatic process (can i save my effort from typing all of them out?)
    e=(Qh-Qc)/Qh

    3. The attempt at a solution
    Substitute the relevant equations in order to get Qc & Qh
    it always seems a lack of information to the three points
    there should be a specific route for substituting the variables to the cycle and the few thought by me should be wrong
    can anyone tell me the right way to get option "e" here?

    Thank you
     
  2. jcsd
  3. Dec 12, 2016 #2

    CWatters

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    Show your working.

    I haven't attempted a solution but usually these come from the data provided on the graph combined with your knowledge about what is constant during an isobaric, isochoric, or adiabatic process.
     
  4. Dec 12, 2016 #3
    isobaric=>p constant
    isochoric=>v constant
    adiabatic=>q constant
     
  5. Dec 12, 2016 #4

    CWatters

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    So of P, V, and T which are you missing at each of the three points and how might you work them out from the info provided?
     
  6. Dec 12, 2016 #5
    You must attempt the question yourself. Get as far as you can and then post that attempt here so that the homework helpers can see where your misunderstanding comes in.
     
  7. Dec 12, 2016 #6
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