Parallel Plate Capacitor

A capacitor essentially consists of two conductors, one charged and the other usually earthed.

Parallel Plate Capacitor

A parallel plate capacitor is one of the simplest capacitors in which two parallel metallic plates, each of area A, are separated from one another by a small distance d. An insulating medium like air, paper, mica, glass, etc separates the plates. The plates are connected to the terminals of a battery.

Suppose that these plates acquire +q and –q charge when the capacitor is fully charged. These charges set up a uniform electric field E between the plates. When the separation d is small compared to the size of the plates, distortion of electric field at the boundaries of the plates can be neglected.

If σ is surface charge density on either plate, the magnitude of electric field between the plates is given by

E = σ/ε₀ = q/ε₀A

The potential difference between the plates is given by

V = Ed

Capacitance of a parallel plate capacitor is given by

C₀ = q/V = ε₀A/d

The capacitance of a parallel plate capacitor is directly proportional to the area of the plates and inversely proportional to their separation. It means that to obtain high capacitance, area of the plates should be large and separation between them should be small.

If the plates of a capacitor are separated by a dielectric material other than air or vacuum, the capacitance of a parallel plate capacitor is given by

C = εA/d = kε₀A/d

C = kC₀