Q. What do you mean by Capacitance?

An ideal capacitor is an energy-storage circuit element (with no loss associated with it) representing the electric-field effect. The capacitance in farads (F) is defined by

C = q/v

where q is the charge on each conductor, and v is the potential difference between the two perfect conductors. With v being proportional to q, C is a constant determined by the geometric configuration of the two conductors. Figure (a) illustrates a two-conductor system carrying +q and -q charges, respectively, forming a capacitor.

The general circuit symbol for a capacitor is shown in Figure (b), where the current entering one terminal of the capacitor is equal to the rate of buildup of charge on the plate attached to that terminal,

i(t) = dq / dt = C dv / dt

in which C is assumed to be a constant and not a function of time (which it could be, if the separation distance between the plates changed with time).