TABLE OF CONTENTS When an emf E (Fig. 16.5a) is applied to the plates of a condenser (see Sec. 7) with a capacity C, an electrostatic field is established between these plates owing to the accumulation of negative and positive charges on their surfaces. The amount of charge Q that accumulates on the plates depends on (1) the potential E impressed on the plates, (2) the area A of the plates, (3) the distance d between the plates, (4) the kind of dielectric occupying the space between the plates, and (5) the time that elapses from the instant of impressing E to the instant of measuring the charge Q.
In most commercial dielectrics, the variation of charge with each of these factors can be ascertained only by experiment. Indeed, there seems to be no general law which all dielectrics do obey. In order to simplify this discussion, assume a perfect dielectric, i.e., one for which there exists a linear relation between Q and E, and Q and A, as well as between Q and 1/ h. Moreover, such a perfect dielectric will have an infinite resistance so that no conduction current will flow through it. Finally, in such a dielectric, Q is independent of time, so that the dielectric will be assumed to take its full charge instantly. With the foregoing assumptions (which, except for time, hold true for air and vacuum),...
