Consider a commonly-used capacitor made from two circular parallel plates with a ceramic dielectric between them. The plates have 12.5 mm diameter and the whole thing is 3 mm thick with a capacitance of 10 nF. Neglecting the finite thickness and extent of the plates, what relative permittivity must the material between the plates have to provide this capacitance? Allowing for the finite thickness of the plates, and of the insulation wrapping the outside of the whole thing, is this an underestimate or overestimate of the permittivity? I'm really not sure how to start at all. Without filling in details, can someone please explain how I would go about this problem?