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Homework Help: Polytropic process

  1. Nov 8, 2006 #1

    I have a question relating to a polytropic process. The question consists of two parts.

    It says that the pressure (p) and the volume (v) of a gas undergoing a polytropic process are related by the equation:

    p1V1^n = p2V2^n (where P1, P2 etc are individual variables as i dont know how to put sub text into the question)
    the question then says...where n is the polytropic index.


    p1V1/T1 = p2V2/T2

    determine an expression for p!, in terms of p2,T1,T2 and n

    I have had a look on the net for help in answering the question but not luck so far.
  2. jcsd
  3. Nov 9, 2006 #2


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    Science Advisor

    I am assuming that you want to find P1 and not P factorial. This should be basic algebra (I hope). It looks like it could be a bit of a trick question because usually you just deal with P and V in a polytropic compression. To calculate T you need to know about the substance.

    If [tex]P_1 V_1^n = P_2 V_2^n[/tex] Then

    [tex]\frac{P_1 V_1}{T_1}=\frac{P_2 V_2}{T_2}[/tex]

    [tex]\frac{P_1 V_1^n}{T_1}=\frac{P_2 V_2^n}{T_2}[/tex]

    [tex]P_1 = \frac{P_2 T_1}{T_2} \left[ \frac{V_2}{V_1} \right] ^n[/tex]
    Last edited: Nov 9, 2006
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