permittivity (electric permittivity)

Permittivity, also called electric permittivity, is a constant of proportionality that exists between electric displacement and electric field intensity. This constant is equal to approximately 8.85 x 10^-12 farad per meter (F/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the free-space value, which is symbolized e_o.

In engineering applications, permittivity is often expressed in relative, rather than in absolute, terms. If e_o represents the permittivity of free space (that is, 8.85 x 10^-12 F/m) ande represents the permittivity of the substance in question (also specified in farads per meter), then the relative permittivity, also called the dielectric constant e_r, is given by:

e_r = e / e_o
= e (1.13 x 10¹¹)