Please stop reading unless you have Kittel's Solid-state physics book. I have the 8th edition.
I am working on problem 6.6 "Frequency dependence of the electrical conductivity". Could someone just give me a total rewording of what is going on in this question? For example, what is [itex]\omega[/itex] and and why doesn't the [itex]\omega[/itex] dependence of [itex]\sigma[/itex] show up in equation (43)?