Insulating Materials

The larger the plate area and the smaller the spacing between the plates, the greater the capacitance. The capacitance also depends on the kind of insulating material between the plates; it is smallest with air insulation. Substituting other insulating materials for air may increase the capacitance many times.

The ratio of the capacitance with some material other than air between the plates, to the capacitance with air between the plates, is called the dielectric constant of the insulating material. The material itself is called a dielectric.

The dielectric constants of a number of common materials in capacitors are shown in this table. For example, if a sheet of polystyrene is substituted for air between the plates of a capacitor, the capacitance will be increased 2.6 times.