Permittivity - Vacuum Permittivity

Vacuum Permittivity

The vacuum permittivity ε₀ (also called permittivity of free space or the electric constant) is the ratio D/E in free space. It also appears in the Coulomb force constant, k_e = 1/(4πε₀).

Its value is

$\begin{align} \varepsilon_0 & \stackrel{\mathrm{def}}{=}\ \frac{1}{c_0^2\mu_0} = \frac{1}{35950207149.4727056\pi}\ \frac{\text{F}}{\text{m}} \approx 8.8541878176\ldots\times 10^{-12}\ \text{F/m} \end{align}$

where

c₀ is the speed of light in free space,

µ₀ is the vacuum permeability.

Constants c₀ and μ₀ are defined in SI units to have exact numerical values, shifting responsibility of experiment to the determination of the meter and the ampere. (The approximation in the second value of ε₀ above stems from π being an irrational number.)

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