permittivity of free space

The permittivity of free space (a vacuum) is a physical constant equal to approximately 8.85 x 10^-12 farad per meter (F/m). It is symbolized _o. In general, permittivity is symbolized and is a constant of proportionality that exists between electric displacement and electric field intensity in a given medium. In many materials, particularly glass and certain plastics, is substantially greater than _o.

If _o represents the permittivity of free space (that is, 8.85 x 10^-12 F/m) and _s represents the permittivity of a particular substance (also specified in farads per meter), then the relative permittivity, also called the dielectric constant _r, of that particular substance is given by:

_r = _s / _o
= _s x 1.13 x 10¹¹

Also see Table of Physical Units and Constants.