Dielectric Material

Introduction to dielectric material:

Dielectrics are insulating materials. In dielectrics all the electrons are bound to their parent molecules and there are no free charges. Even with normal voltage or thermal energy electrons are not released. Dielectrics are non metallic materials of high specific resistance and have negative temperature coefficient of resistance.


Dielectric Constant and electric polarization:


Dielectric Constant  ( `epsi`r ) :   The dielectric characteristics of a material are determined by the dielectric constant or relative permittivity      `epsi`r  of that material. It is the ratio between the permittivity of the medium and the permittivity of  free space .

i.e.,      `epsi_r`  =  `(epsi)/(epsi_0)`  .  Since it is the ratio of same quantity, `epsi_r`  has no unit. It is a measure of polarization in the dielectric material.

Electric Polarization :  Let us consider an atom placed inside an electric field. The centre of positive charge is displaced along the applied field direction. Thus a dipole is produced. When a dielectric material is placed inside an electric field such dipoles are created in all the atoms inside. This process of producing electric dipoles which are oriented along the field direction is called polarization in dielectrics.


Important applications of dielectric materials:


Dielectrics are very widely used as insulating materials.

1. Electrical conductors made of Aluminium Copper which are used for electric wiring are insulated with a  outer jacket of plastic or rubber.

2. In heater coils ceramic bead are used to avoid short circuiting as well as to insulate the outer body from electric current.

3. In electric iron, mica or asbestos insulation is provided to prevent the flow of electric current to the outer body of the iron.

4. In transformers as well as in motor and generator windings varnished cotton is used as insulator.

5. In electricity distribution lines, porcelain structures are used as insulators between points of different potential. In between aluminium or steel - cored aluminium conductors running through different distribution points, acts as insulator.