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: Intensive or extensive variables.

  1. Oct 9, 2006 #1
    Hello,
    In my book:
    [PLAIN]http://img84.imageshack.us/img84/6264/variabelwk1.jpg[/PLAIN] [Broken]

    But why do the tell me that the need do discribe the extensieve state of a system by using intensive and at least one extensive variable?

    Thanks a lot.
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Dec 22, 2011 #2
    Hello Bert: you are probably retired from PF by now but the issue might be interesting for others too:
    we take a system consisting of 1 kind of species present (we take helium). internal energy U is an extensive quantity so we need 1+2=3 variables to know it. But U=n(3/2)RT, so here two variables seem to be sufficient, with n extensive and T intensive. In general thermodynamics takes U=U(S,V) which also has only 2 varibles, but for G=G(p,T) 2 would not be enough because both p and T are intensive. ??
    Sorry for the mess.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook