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Entropy and Temperature
Two crucial concepts of Thermodynamics that spring directly from our work in the previous
section are entropy and temperature. Here we define both and discuss how they relate to their
more common definitions.
Entropy
We begin by revisiting the multiplicity function we looked at earlier. Let us modify the function
slightly, so that instead of being a function of
N
and
N
up
, the total number of particles and the
number of up magnets, let us generalize and let
g
now be a function of
N
and
U
, the energy of
the system at hand. Now, this does not alter the definition at all;
g
still represents the number of
states of the system with the same value of a particular variable, though in this case that variable
is the energy
U
.
The entropy is defined as:
σ
(
N
,
U
)âÉálog
g
(
N
,
U
)
Notice that entropy is unitless. (Here, log is used to represent the natural logarithm, ln .) You
might wonder why the entropy is defined this way. We will get at the answer via a short
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This note was uploaded on 02/09/2012 for the course PHY PHY2053 taught by Professor Davidjudd during the Fall '10 term at Broward College.
 Fall '10
 DavidJudd
 Physics, Work, Entropy

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