Dielectric And Its Effects


Energy in the electric field in a dielectric

where is the dielectric constant



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.


Dielectric constant

The ratio of permittivity of a medium to the permittivity of free space is known as the dielectric constant or relative permittivity of the medium. It is denoted by or .

where for free space


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.