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Homework Help: Gas Cycle Process; Adiabatic, Isovolumetric and Isothermal

  1. Jun 8, 2010 #1
    1. The problem statement, all variables and given/known data

    A monatomic gas has V1 P1 and T1 (volume pressure and temp) at state 1
    The gas then goes through the following process

    adiabatic expansion to stage 2 (exapands to twice its volume)
    isovolumetric heating so it gets back to T1; stage 3
    isothermal compression back to intial state

    2. Relevant equations
    - Sketch on pV diagram? (done this)
    - derive expressions for P2 and P3 (in terms of p1 and [tex]\gamma[/tex]) ?
    - derive expressions for T2 and T3 (in terms of T1 and [tex]\gamma[/tex])?

    - expression for net work done in 1 cycle?
    - is this an engine or refridgerator?

    3. The attempt at a solution

    i've managed to find

    P2 = P1 / (2^[tex]\gamma[/tex])
    and that [tex]\gamma[/tex] = 5/3

    The 2 questions in bold are the ones really stressing me out; if someone could please put up some solutions or just point me in the right way that would be great :)
  2. jcsd
  3. Jun 9, 2010 #2


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    Can you find p3 in terms of p1? What is the equation for an isotherm? Use it the same way you used the adiabatic equation to find the relation between the two pressures. Once you have p2 and p3 in terms of p1, use the ideal gas Law to get the temperatures.
  4. Jun 9, 2010 #3
    The isotherm eqn; W = nRT*ln(vi/vf)
    where vi = v1 and vf = v3?
  5. Jun 9, 2010 #4


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    That's the work for an isothermal process. How about p1V1=p3V3? A straightforward result of the ideal gas law.
  6. Jun 9, 2010 #5
    Ah ofcourse :| .. Sounds like me to over think the simple(correct) answer

    Thank you :)
    - i'll post on here if i can't figure the rest
    Last edited: Jun 9, 2010
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