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Total Energy

  1. Mar 23, 2009 #1
    In my notes,

    http://www.ph.ed.ac.uk/~pmonthou/Statistical-Mechanics/documents/SM3.pdf [Broken]

    on page 1 we are told we're dealing with systems of fixed total E but in the expilicit example on page 3, do we not find 4 different values for the total energy. how is this possible?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 23, 2009 #2

    Ben Niehoff

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    Right. The point is to look at how many different microstates (arrangements of up/down spins) correspond to the same macrostate (total energy). This is used to give us entropy as a function of total energy, S(E).

    Notice that total energy is still an input parameter. So once we find the function S(E), we can fix E to be any particular allowed value.
     
  4. Mar 23, 2009 #3
    yes but this is supposed to be an isolated system hence E is fixed

    yet in the table we have E being -3mH, -mH +mH, +3mH which means it's not fixed. i guess i just cant really follow your argument sorry
     
  5. Mar 23, 2009 #4

    Ben Niehoff

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    We're not talking about a single system, but an ensemble of many possible systems. Each of those systems has a different energy and entropy. Your notes describe how to find the entropy as a function of energy, S(E).

    Once we know S(E), we can then calculate properties of any particular system of some given energy E.
     
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