### 9.1.1. Constitutive Relationships

The electric field and the electric displacement are related through the polarization vector as:

| (9–6)

where is the permittivity of vacuum. For linear materials (typically diamagnetic or paramagnetic), the polarization vector can be written as

| (9–7)

where is the electric susceptibility, which can be a function of the electric field .

A similar relationship is used to relate the magnetic induction to the magnetic field , and the magnetization vector .

| (9–8)

where is the permeability of vacuum. For linear materials, the magnetization vector can written as

| (9–9)

where is the magnetic susceptibility.

Finally, for the current density can be written as

| (9–10)

where is the electrical conductivity.

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