Electric susceptibility

A dimensionless parameter measuring the ease of polarization of a dielectric. In a vacuum, the electric flux density D (measured in coulombs/m² and electric field strength E (volts/m) are related by Eq. (1) where e is

D = ε₀E (1)

the permittivity of free space, having the value 8.854 x 10^-12 farad/m. In a dielectric material, polarization occurs, and the flux density has the value given by Eq. (2), where E_r is the relative

D = ε₀ε_r E = ε₀E + P (2)

permittivity of the material and P is the polarization flux density. This can be written as Eq. (3), where Χ_e = ε_r - 1 is known as the

P = ε₀(ε_r — 1)E = E₀Χ_eE

electric susceptibility of the dielectric material. It's a measure of that part of the relative permittivity which is due to the material itself.

The electric susceptibility can be related to the polarizability a by expressing the polarization in terms of molecular parameters. Thus Eqs. (4) hold, where N is the number of molecules per unit

P = N(μ)_avg = N_αE_L

Χ_e =((N_αE_L)/e₀E))

volume, (μ_avg) is their average dipole moment, and E_L is the local electric field strength at a molecular site. At low concentrations, E_L approaches E, and the susceptibility is proportional to the concentration N. For a discussion of the properties and measurement of electric susceptibility Google POLARIZATION OF DIELECTRICS.

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