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Calculation actual efficiency problem

  1. Oct 31, 2013 #1
    1. The problem statement, all variables and given/known data

    A heat engine takes in 1030 J of energy at 1000 K and exhausts 585 J at 250 K. What are the actual and maximum theoretical efficiencies of this heat engine?

    2. Relevant equations

    For maximum efficiency I got 75 % by taking 1 - (250K / 1000K). For actual efficiency the equation is W/ Q or work out / heat in.

    3. The attempt at a solution

    I am not sure where to start on this problem and any help would be very nice!
     
  2. jcsd
  3. Oct 31, 2013 #2

    CWatters

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    The max efficiency is the Carnot efficiency which you seem to have right (I think).

    As for the actual efficiency...
    Correct.

    If 1030 J goes into the engine and 585J comes out of the exhaust how much is used elsewhere by the engine, presumably doing useful work?
     
  4. Oct 31, 2013 #3
    445 j?
     
  5. Oct 31, 2013 #4

    haruspex

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    Yes.
     
  6. Oct 31, 2013 #5

    CWatters

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    So if 1030J goes in and only 445J comes out in the form of useful work the efficiency is ?
     
  7. Nov 1, 2013 #6
    445 J / 1030 J = 43 % thanks very much!
     
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