author

Akshit Sharma

teacher | Maths Physics Chemistry

Description

Myself Akshit Sharma a graduate with passionate to learn and teach. I am pretty good in Mathematics while i do have teaching experience and good exposure in Physics and Chemistry as well.

Qualification

B.Sc

Experience

1-3 Years

Teaching Classes

11-12

Current Organization

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

Dielectrics – Polar and Non-Polar Dielectrics

Dielectrics are insulating (non-conducting) substances which transmits electric effect without conducting. It has no free electrons.

                                         

There are two types of dielectrics –

 

1.      Polar dielectrics: Like water, alcohol, CO2, NH3, HCL. etc are made of polar atoms/molecules.

 

A polar molecule has permanent electric dipole moment in the absence of electric field also. But a polar dielectric has net dipole moment zero in the absence of electric field because polar molecules are randomly oriented.

In the presence of electric field polar molecules trends to line up in the direction of electric field, and the substances has finite dipole moment.

If Eext is the external field applied and Ein is the field due to alignment of dipoles.

 

2.      Non polar dielectrics: Like N2, O2, Benzene, Methane, etc are made of non-polar atoms/molecules.

 

In non-polar molecules, when no electric field is applied the centre of positive charge coincides with the centre of negative charge in the molecule. Each molecule has zero dipole moment in its normal state.

When electric field is applied, positive charge experiences a force in the direction of electric field and negative charge experiences a force in the direction opposite to the field i.e. molecules becomes included electric-dipole.

If Eext is the external field applied and Eind is the field induced.

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