The permittivity of free space has been represented as ε 0 and is equal to 8.85 × 10–12 F/m. The permitivity of any dielectric material can be represented as ε and it is equal to εr ε0 i.e.,
where εr is called the relative permittivity or dielectric constant of the dielectric material. It is a dimensionless quantity.
The dielectric constant can also be obtained from electric flux density (D) and an applied electric field (E).
The number of electric force lines passing per unit area perpendicular to field is called electric flux density (D). It is proportional to the applied electric field (E).
So D ∝ E or D = εE ...