Non-polar and polar dielectrics

Non-polar and polar dielectrics –

In this topic we will discuss about Non-polar and polar dielectrics and dielectric polarization with electrical susceptibility.

Non polar and polar dielectrics  –

As we know the dielectrics are insulating material which transmit electric effect without conducting electricity .

Dielectrics is of two types , Non-polar Dielectrics and polar Dielectrics .

In non-polar dielectric ,  in the molecule of the dielectric the centre of mass of the positive charge coincide with the centre of mass of the negative charge . Like , Hydrogen , nitrogen , oxygen , carbon dioxide , methane , benzene etc . In such kind of molecule each molecule has zero dipole moment and they are symmetric in shape .

But in case of polar dielectric . The  centre of mass of positive and negative charges do not coincide  because of the asymmetric shape of the molecules. It has permanent dipole moment . example – HCl , NH3 H2O, alcohol etc .

Dielectric polarization –

When a non polar dielectric is held in external electric field , the two centres of positive and negative charges in the molecules are separated . The molecules gets distorted and is said to be polarized as a small dipole moment .

The dipole moment acquired is given as , p = αϵ0E0  Where α is the constant of proportionality called molecular polarizability .  Its unit is m3 .

If N is the number of atoms per unit volume then , electric polarization P = N p   or,  P = N qx .

Its unit is C-m-2

If we consider a small volume element in the interior of the slab  as shown in figure . , each volume has no net charge ,though it has net dipole moment . This is because positive charge of each dipole sits close to the negative charge of the adjacent dipole . . The negative end of the dipole remain un-neutralized  at the surface AB and positive end of the dipole at CD . then the effective electric field E = E0 -EP  ;

Further EP = σ/ϵ =  p/ϵ.

Electric susceptibility –  As we know that the electric polarization P αE    or, p= ϵ  χ E

Where  χ is constant called electrical susceptibility .

For vacuum χ = 0 ;

But as we know ,   E = E0 -EP  = E0 – P/ϵ = E0  –  ϵ  χ E/ϵ

Or , E = E0 -χE  ;

E0 = E  +   χ E  = E( 1+ χ )

OR ,             E0/E  =  1 + χ

K ( Dielectric constant or relative permittivity ) = 1 + χ   [ since  K= E0/E  ]

K (ϵr) = 1 +  χ …………………This is the relation between relative permittivity and susceptibility .

475 thoughts on “Non-polar and polar dielectrics