Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Meaning of formula from statistical physics

  1. Mar 19, 2006 #1
    Hi.

    Can anyone explain the meaning of this formula from statistical physics to me:

    [tex]S = -k\sum_r{p_r\ln p_r}[/tex]​

    Ok, I know that S is the entropy, the p's are probabilities of some sort - but somehow this is not satisfactory :-)
     
  2. jcsd
  3. Mar 20, 2006 #2
    What this formula tells you is that for each state of macroscopic equilibrium there corresponds a large number of possible microscopic states or molecular configurations. The entropy, s, of a system is related to the total number of possible microscopic states of that system, called the thermodynamic probability p, by the Boltzmann relation:

    [tex] S= k*ln(p) [/tex]

    So from a microscopic point of view, the entropy of a system increases when the molecular randomness or uncertainty increases.

    (stole most of that from my text book but, eh, gets the job done :tongue:)
    Edit: Your formula is slightly different from mine. It appears that yours takes on the form of a probability mass function, where the sum over all r should equal to one.
     
    Last edited: Mar 20, 2006
  4. Mar 20, 2006 #3
  5. Mar 20, 2006 #4
    Ok, thanks guys!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Meaning of formula from statistical physics
  1. Statistical Physics (Replies: 4)

  2. Statistical Physics (Replies: 2)

  3. Statistical Physics (Replies: 2)

Loading...