# Permittivity of free space

The permittivity of free space, ε0, is a physical constant used often in electromagnetism. It represents the capability of a vacuum to permit electric fields. It is also connected to the energy stored within an electric field and capacitance. Perhaps more surprisingly, it's fundamentally related to the speed of light. The permittivity of free space, ε0, is defined as:[1]

where

An electric field, , in a region of space has field energy associated with it, that energy density is:[2]

The energy stored in a capacitor (with no dielectric) is:

Energy

where

• is the area of the plates,
• is the distance between the plates
• is the voltage between the plates.

The permittivity of free space can also be used to find the Coulomb force. The constant gives how strong the force is between two charges separated by a distance:[1]

where

• is the Coulomb force,
• and are two charges, and
• is the separation between the charges.