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What is dielectric polarization and dielectric susceptibility? Find the relation between them.

Mumbai university > FE > SEM 1 > Applied Physics 1

Marks: 5M

Year: Dec 2013

1 Answer
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Dielectric Polarization

  • When a Dielectric material is subjected to an external electric field, the polar molecules rearrange themselves along the electric field giving rise to net dipole moment.

  • This phenomenon is called Dielectric Polarization.

  • The induced dipole moment per unit volume of the dielectric is called Polarization vector (P).

Dielectric Susceptibility

  • It is a dimensionless proportionality constant that indicates the degree of polarization of a dielectric material in response to an applied electric field.

  • The greater the electric susceptibility, the greater the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material.

The Relation

Consider a parallel plate capacitor with a dielectric medium of constant εr placed between the two plates

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Polarization of Dielectric Medium between Two Capacitor Plates If σ is the Charge per unit area of the surface of the plate, then by using Gauss’ Theorem, we have,

E0=σε0

Also,

Ei=σpε0

Where, σp is the charge per unit area of the surface of the slab

The resultant electric field (E) is given by,

E=E0Ei=σε0σpε0

∴ ε_0 E = σ - σ_p

The magnitude of polarization P = σ_p, And the Electric Flux Density D = σ = ε_0 ε_r E

∴ ε_0 E = P - ε_0 ε_r E

∴ P = ε_0 (ε_r - 1)E

Or,

P = ε_0 χE

Where,

χ = (ε_r-1)

…And is called Dielectric Susceptibility.

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