Capacitance of two parallel plates
The most common capacitor consists of two parallel plates. First, we derive the capacitance which depends on the area of the plates A and their separation d. According to Gauss's law, the electric field between two plates is:
Since the capacitance is defined by one can see that capacitance is:
Thus you get the most capacitance when the plates are large and close together.
If a dielectric material is inserted between the plates, the microscopic dipole moments of the material will shield the charges on the plates and alter the relation. Materials have a permeability e which is sometimes given by the relative permeability k, e=ke0. The capacitance is then given by: