# electric susceptibility

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## Electric susceptibility

A dimensionless parameter measuring the ease of polarization of a dielectric. In a vacuum, the electric flux density **D** (measured in coulombs/m^{2}) and electric field strength **E** (volts/m) are related by Eq. (1) where

(1)

ε_{0}is the permittivity of free space, having the value 8.854 × 10

^{-1}

^{2}farad/m. In a dielectric material, polarization occurs, and the flux density has the value given by Eq. (2),

(2)

where ε_{r}is the relative permittivity of the material and

**P**is the polarization flux density. This can be written as Eq. (3), where &khgr;

_{e}=

(3)

ε_{r}- 1 is known as the electric susceptibility of the dielectric material. It is 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 α by expressing the polarization in terms of molecular parameters. Thus Eqs. (4)

(4)

hold, where *N*is the number of molecules per unit 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

*See*Permittivity, Polarization of dielectrics

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

## electric susceptibility

[i¦lek·trik sə‚sep·tə′bil·əd·ē] (electricity)

A dimensionless parameter measuring the ease of polarization of a dielectric, equal (in meter-kilogram-second units) to the ratio of the polarization to the product of the electric field strength and the vacuum permittivity. Also known as dielectric susceptibility.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.