- #1
msaleh87
- 8
- 0
Homework Statement
For a system A consists of two parts A' and A'' which interact only weakly with each other, if the states of A' and A'' are labeled respectively by r and s, then a state of A can be specified by the pair of numbers r,s and its corresponding energy [itex]E_{rs}[/itex] is simply additive, i.e.,
[itex]E_{rs}[/itex] = [itex]E^{'}_{r}[/itex] + [itex]E^{''}_{s}[/itex]
The partition function Z for the total system A is a sum over all states labeled by rs, i.e.,
Z=[itex]\sum_{r,s}e^{-\beta(E^{'}_{r}+E^{''}_{s})}[/itex] = [itex]\sum_{r,s}e^{-\beta E^{'}_{r}} \ e^{E^{''}_{s}}[/itex] = ([itex]\sum_{r}e^{-\beta E^{'}_{r}}[/itex])([itex]\sum_{r}e^{-\beta E^{''}_{s}}[/itex]) = [itex]Z^{'}Z^{''}[/itex]
My question is: how the sum of product [itex]\sum ()()[/itex] is converted to product of sum ([itex]\sum[/itex])([itex]\sum[/itex]), they are not generally equal
Thanks
Last edited: