1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How To Find Work If I have Pressure and Volume

  1. Mar 28, 2008 #1
    I have

    P_1 = 1 x 10^5 Pa
    p_2 = 11.764x10^5 Pa

    V_1 0.826 m^3
    V_2 0.142 m^3


    Expansion / Compression Index of 1.4

    I need to calculate Work Done.

    First of all i identify 1-2 as an Isothermal Process, which gives equation.

    W = P_2 * V_2 * ln (V_2 / V_1)

    If i use that formula i get an answer.

    What i am unsure of is

    1) Am i using the right formula based on what data i have, i only have data that i have above.

    2) How and what do i use expansion and compression index for?

    Thanks for any help, needed urgent to solve a question.
  2. jcsd
  3. Mar 28, 2008 #2


    User Avatar
    Homework Helper

    If you are given an index of 1.4, you are probably supposed to be looking at an adiabatic process for a diatomic gas. So you don't want to use the work formula for an isothermal process.

    In a (reversible) adiabatic process, the relationship is [tex]P_{1}V_{1}^{\gamma} = P_{2}V_{2}^{\gamma}[/tex], where gamma is the adiabatic index (in your case, [tex]\gamma = 1.4[/tex]). In such a process, Q = 0 ; you would still calculate work by integrating P dV between the two values for volume, but the result is now a little more complicated...
    Last edited: Mar 28, 2008
  4. Aug 31, 2008 #3
    well if u r talking abt the work done in a cycle then it is

    Workdone/cycle = n/n-1 x P1V1 x [ (P2/P1)power n-1/n - 1 ]

    but put pressure in KN/m2 this will give u the answer in KJ/minute, and if u divide the answer by 60 then it will b Kilo-Joules/Sec that is Watts, so that will b the Power in KW.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook