####
Terms

**
Boltzmann Factor
** -
Any term of the form *e*^{-/τ} is called a Boltzmann
Factor.

**
Gibbs Factor
** -
Any term of the form *e*^{(Nμ-)/τ} is called a Gibbs factor.

**
Gibbs Sum
** -
The Gibbs Sum is the sum of all of the Gibbs Factors for the states and numbers of a system, and is given by:

*Z*_{G}(

*μ*,

*τ*) =

*e*^{(Nμ-)/τ}**
Partition Function
** -
The Partition Function represents the sum of all of the Boltzmann Factors for the states of a system, and is given by:

*Z* =

*e*^{-/τ}**
Planck distribution function
** -
The Planck distribution function describes the average number of photons

< *s* > in a particular frequency

*σ* for blackbody radiation and is given by:

<

*s* > =

**
Stefan-Boltzmann law of radiation
** -
The Stefan-Boltzmann law of radiation gives the energy density of radiation in a cavity, as can be expressed:

=

*τ*^{4}####
Formulae

**
The probability of finding a system in energy state if the system is in thermal contact with a reservoir
** | *P*( ) = |

**
The entropy of blackbody radiation
** | *σ* = ( ) ^{3} |