1. 3 conducting spheres of radius a, b, c (a<b<c) are held at a potential of 0, V, 0 respectively. What is the capacitance of the system? 2. Q=CV (which I assume extends to Qi=CijVj for multiple conductors). 3. I've calculated the fields in the two interesting regions, calculated the charge on each sphere - this gives Qa+Qb+Qc=0. I can't find many references to the "total capacitance" of a system of conductors and how it would relate to my Cij. I might be missing the totally obvious, but that'll be down to my utter incompetence when it comes to physics! Thanks for shedding any light on the matter. It shouldn't be too difficult, because the question comes from an undergraduate example sheet on introductory EM.