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: Pressure on system and work done by the system

  1. Sep 27, 2014 #1
    A certain insulating material has 5 x 1022 atoms, each having six degrees of freedom. It initially occupies a volume of 10-6 m3 at a pressure of 105 Pa. The pressure and volume are related by p(V - V0) = constant, where V0 = 0.94 x 10-6 m3

    2. Relevant equations
    [tex]W = -\int p\, dV[/tex]
    PV = nRT
    [tex]\bigtriangleup E = \bigtriangleup Q - \bigtriangleup W[/tex]
    PiVi = PfVf

    3. The attempt at a solution

    This one is confusing because it gives me one initial volume, and then gives me a V0 that's almost the same as the initial volume, so I don't know if I only use the V0 for that equation with the constant, or if I use that as the initial volume for something else. No idea why it gives me two different (but almost identical) initial volumes.
    I solved for the constant, using the initial volume and the other initial volume for V, and then tried to use that constant and plugging in what I had in V in for V0 and solving for the V, which would be the final volume, and then plugging that into the limits of integration. That did nothing good.

    I tried solving for the final volume, using PiVi = PfVf and then plugging that into my limits of integration, and multiplying P times ten. That didn't work.

    I tried using PV = nRT and solving for T, but I don't know what to do with T. But the question gives me numbers of atoms, which is why I tried using the ideal gas law. Otherwise it would have been irrelevant information, as far as I can tell. It's an insulating material, so I guess it's not an ideal gas. It's probably a solid.
    It gives me the degrees of freedom of the atoms. I have no idea how that's relevant.
  2. jcsd
  3. Sep 27, 2014 #2
    I forgot to ask the question and I can't edit. But I figured out that part. The next part asks "Suppose that the potential energy per particle remains constant, and that the pressure increases sufficiently quickly that no heat enters or leaves the system during the process, ie, the process is adiabatic. By how much does the temperature of the insulator rise?"

    I tried the ideal gas law, but it's not a gas, so I don't think it applies. I'm getting an answer with that equation that's close to the real answer; it has the same order of magnitude, but it's not close enough. I need something that relates pressure, temperature, moles, and volume, that can be relevant to a solid. I'm assuming it's a solid, and I don't think the ideal gas law applies to solids.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted