In particular, if the electric susceptibility is introduced through the approximation:

This changes P, and the result is electric susceptibility (and hence permittivity).

Under transient conditions, the displacement field can be expressed as (see electric susceptibility):

In analogy to magnetic susceptibility, electric susceptibility only occurs above T.

Here χ is not a number as before but a tensor of rank 2, the electric susceptibility tensor.

The hyperpolarizability, a nonlinear-optical property of a molecule, is the second-order electric susceptibility per unit volume.

A more general version of this model (which allows the polarization to vary with position) is the customary approach using electric susceptibility or electrical permittivity.

The polarizability of individual particles is related to the average electric susceptibility of the medium by the Clausius-Mossotti relation.

By contrast, the electric susceptibility is unitless in both systems, but has different numeric values in the two systems for the same material:

The electric susceptibility χ of a dielectric material is a measure of how easily it polarizes in response to an electric field.

For the actual calculation of P due to an applied electric field, however, the electric susceptibility χ of the dielectric must be known (see below).

In SI units, permittivity ε is measured in farads per meter (F/m); electric susceptibility χ is dimensionless.

As a result, by measuring the threshold electric field one can effectively measure the twist Frank constant so long as the anisotropy in the electric susceptibility and plate separation is known.

Electric susceptibility is defined as the constant of proportionality (which may be a tensor) relating an electric field E to the induced dielectric polarization density P such that:

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 (and store energy).

In electromagnetism, the electric susceptibility (latin: susceptibilis "receptive") is a dimensionless proportionality constant that indicates the degree of polarization of a dielectric material in response to an applied electric field.

More formally, it states that the coefficient of the second order electric susceptibility response () is proportional to the product of the first-order susceptibilities () at the three frequencies which is dependant upon.

It is in this way that the electric susceptibility influences the electric permittivity of the material and thus influences many other phenomena in that medium, from the capacitance of capacitors to the speed of light.

At the microscale, an electromagnetic wave's phase speed is slowed in a material because the electric field creates a disturbance in the charges of each atom (primarily the electrons) proportional to the electric susceptibility of the medium.

The topic did not appeal to Rabi, but after William Lawrence Bragg gave a seminar at Columbia about the electric susceptibility of certain crystals called Tutton's salts, Rabi decided to research their magnetic susceptibility, and Willis agreed to be his supervisor.