There are two ways you can represent your component diagram, viz
 Have one component diagram per use case, so it will be 3 or 4 depending on number of use cases(Refer worked out example in Mark Cade and Simon ).
 One component diagram for all usecases ( Refer chapter 9 of Cade and Sheil book ).
In fact, I have done both versions in my assignment.
Bottomline, does not matter whether you use 1 or 2 or both in the above, you should clearly seggregate the Tiers/Layers, if you use color for your diagram, then clearly state color coding explanation ( suggestion by cade and sheil in chapter 9).