Dielectric constant, breakdown, strength and polarization

Dielectric Constant is defined as the ratio of Eext/Enet = K, where K is called dielectric constant.


·         K is also known as relative permittivity (Er) of the material.

·         The value of K is always greater than one.

·         For vacuum there is no Em and hence K-1

·         For air K = 1.00054 = K for vacuum.

·         For perfect conductor Em = 0, hence K= infinity.


Dielectric breakdown and dielectric strength


If a very high electric field is created in a dielectric, the outer electrons may get detached from their parent atoms. The dielectric then behaves like a conductor. This phenomenon is known as dielectric breakdown.


The maximum value of electric field (or potential gradient) that a dielectric material can tolerate without its electric breakdown is called its dielectric strength.


S.I. unit of dielectric strength of a material is V/m.


Polarization of a dielectric slab Suppose a dielectric slab is inserted between the plates of a capacitor having charge Q and –Q as shown in the figure.

If charge on plates are +Q and –Q and area of the plates are A Q, is induced charge

Post By : Akshit Sharma 25 Dec, 2018 2491 views Physics