Electrical Engineering ⇒ Topic : Parallel Plate Capacitor

A parallel plate capacitor consists of two large plates separated by a small distance between them. A dielectric material is placed between the plates as shown in Fig. The plates are separated by a distance d. Let the area of plate be A and Er be K. Assume that the electric field between the two plates is uniform and the firing field at the ends is neglected.

                                                             Parallel plate capacitor

 If q is the charge on each plate, then the charge density on each plate will be

Let V be the potential difference between the plates. Then 

Therefore, the capacitance of a parallel plate capacitor is

The capacitance of a parallel plate capacitor is directly proportional to the area of the plate and the permittivity of the dielectric medium and is inversely proportional to the distance between the plates. This suggests that the capacitance of a mica filled capacitor is more than that of an air filled capacitor for the same physical dimensions. Values of the dielectric constant (Er = K) of some important dielectric materials used in capacitors.