In many capacitors there is an insulating material such as paper or plastic between the plates. Such material, called a dielectric, can be used to maintain a physical separation of the plates.There are non – conductors up to a certain value of field depending upon theirnature. If the field exceeds the limiting value, called dielectric strength, dielectric loses its insulting property and begins to conduct.
What is a Dielectric Constant?
When a dielectric material is placed between the plates of a capacitor, the capacitance of the capacitor increases.The ratio of the capacitance of a given capacitor with the material filling theen tire space between its plates to the capacitance of the same capacitor in vacuum is called dielectric constant of that material.
The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. It is an expression of the extent to which a material concentrates electric flux, and is the electrical equivalent of relative magnetic permeability.
K = ε/ ε₀
Now, the ratio of the capacitance of the capacitor with a dielectric medium to the capacitor with vacuum between theplates can be given as,
Dielectric Constant (K) = C/ C₀.
As the dielectric constant increases, the electric flux density increases, if all other factors remain unchanged.
In the below table, we show some dielectric material with their dielectric constant. Experiments indicates thatall dielectric materials have K > 1. Note that every dielectric material has a characteristic dielectric strength which is the maximum value of electricfield before breakdown occurs and charges begin to flow.
|Material||K||Dielectric Strength (10⁶ V/ m)|
|Glass||4 – 6||9|