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Polarisation in Dielectric (Short Notes)

Definition:
When an external electric field is applied to a dielectric, positive and negative charges shift in opposite directions, creating electric dipoles. This is called polarisation.

Formula:
P = χₑ ε₀ E
where,
P = Polarisation, χₑ = Electric susceptibility, ε₀ = Permittivity of free space, E = Electric field.

Types of Polarisation:

1. Electronic: Shift of electron cloud.


2. Ionic: Displacement of ions in crystals.


3. Orientation: Alignment of permanent dipoles.


4. Space-charge: Accumulation at interfaces.



Effects:

Reduces internal electric field.

Increases capacitance.


Relation:
ε = ε₀(1 + χₑ) , K = 1 + χₑ