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PV diagrams for ideal gas

  1. Aug 22, 2014 #1
    1. The problem statement, all variables and given/known data
    Imagine a graph of pressure in kPa (y-axis) against volume in L (x-axis). There is a straight line moving from point A at 300kPa, 0.5L to point B at 500kPa, 1L. The false origin on this graph is 200kPa, 0L. What is the work done by the gas?


    2. Relevant equations

    W=pV

    3. The attempt at a solution
    I know that work is area under graph so its basically the area of a triangle plus area of trapezium. But this gives work = 100J but textbook says 200J. Where have I gone wrong?
     
  2. jcsd
  3. Aug 22, 2014 #2

    ehild

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    See the picture . You need the blue area from the really zero pressure.

    ehild
     

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  4. Aug 22, 2014 #3

    Andrew Mason

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    Use the formula for area of a trapezoid: (L1 + L2)/2 x W

    AM
     
    Last edited: Aug 22, 2014
  5. Aug 22, 2014 #4

    ehild

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    You meant trapezoid, I think :smile:

    ehild
     
  6. Aug 22, 2014 #5

    Andrew Mason

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    Right. A trapezoid.

    AM
     
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