Advanced Knowledge of Polarisation of Dielectrics



Energy in the electric field in a dielectric

where is the dielectric constant


Electric field due to a point charge placed in an infinite dielectric

where is the point charge placed inside an infinite dielectric and is the distance at which the electric field is calculated.



Dielectrics are non-conducting substances which are the insulating materials and are bad conductor of electric current.
Mica, Plastics, Glass, Porcelain and Various Metal Oxides and even dry air is also example of dielectric.


Permittivity and relative permittivity

where is the relative permittivity, is the resultant electric field and is the applied electric field. 
The permittivity is


Electric polarization of matter

Polarization occurs when an electric field distorts the negative cloud of electrons around positive atomic nuclei in a direction opposite the field.  By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites.The polarization process always involves the use of a charged object to induce electron movement or electron rearrangement.


Dielectric strength

The maximum electric field that a dielectric medium can withstand without breakdown (of its insulating property) is called its dielectric strength.
For air, it is
This puts a restriction on the value of capacitance of a given size and is the reason why capacitors are in the range of


Dielectric Constant

n parallel plate capacitor, when dielectric slab is placed between the two plates then the ratio of the applied electric field strength to the strength of the reduced value of electric field capacitor is called dielectric constant that is:

K = Dielectric constant

E = Net Field


Effect of dielectric on capacitance

The larger the dielectric constant, the more charge can be stored. Completely filling the space between capacitor plates with a dielectric increases the capacitance by a factor of the dielectric constant
C = KC'
Where C= New capacitance after introduction of dielectric
C' = C
apacitance with no dielectric between the plates.


Effect of electric field on dielectric material

Dielectric are non-conducting substances and have negligible number of charge carriers.
When a conductor is placed in an external electric field, free charges move such that the net field inside the conductor is zero. This is not possible in a dielectric.
In a dielectric, the electric field induces dipole moment by reorienting the molecules of the dielectric. This causes an electric field opposing the external electric field. Hence, the electric field inside a dielectric is smaller than the original electric field. 


Properties of Dielelctrics

1. Dielectrics does not have any free charges.
2. When an electric field is applied there is small displacement of bound charges creating small  electric dipoles within the dielectric. This phenomenon is called Polarization
3. The electric field inside and outside a dielectric gets modified due to presence of dipoles.
4. Dielectrics can store energy.


Polar dielectric

If in any dielectric substance the centre of positive charge and centre of negative charge of each molecule do not coincide, then such type of dielectric material is called polar dielectric.
Ex : water and HCl 


Non-polar dielectric

If in a substance the centre of positive charge and centre of negative charge of each molecule coincide with each other, because of symmetry of molecules, then these substances are called non-polar dielectric substances.
Ex: etc.


Dielectrics-Polar and Non-polar Dielectric Molecules


Basic Knowledge of Polarisation of Dielectrics


Quick Summary With Stories

Important Questions