Definition:Vacuum Permittivity/Also known as

Vacuum Permittivity: Also known as
The vacuum permittivity is also known by the terms:


 * permittivity of free space
 * permittivity of empty space
 * permittivity in (or of) vacuum
 * distributed capacitance of the vacuum

The term electric constant has now apparently been accepted by many standards organisations worldwide.

However, as from $20$ May $2019$, the definition of $\varepsilon_0$ is no longer as a defined constant, but derived ultimately from the fine-structure constant, which is a measured value.

Hence many authorities (including ) prefer not to use electric constant.

The following terms are more or less obsolete:


 * dielectric constant
 * dielectric constant of vacuum

Note that the term dielectric constant is also still used sometimes to mean the absolute permittivity (of a material), and so suffers the additional problem of being ambiguous.

Some sources use $\epsilon_0$ instead of $\varepsilon_0$.

Either symbol is acceptable, but (having to choose one or the other) has settled on $\varepsilon_0$ as standard.