Vacuum Permittivity

The physical constant ε₀, commonly called the vacuum permittivity, permittivity of free space or electric constant is an ideal, (baseline) physical constant, which is the value of the absolute (not relative) dielectric permittivity of classical vacuum. Its value is:

ε₀ ≈ 8.854 187 817 620... × 10−12 farads per metre (F·m−1).

This constant relates the units for electric charge to mechanical quantities such as length and force. For example, the force between two separated electric charges (in the vacuum of classical electromagnetism) is given by Coulomb's law:

where q₁ and q₂ are the charges, and r is the distance between them. Likewise, ε₀ appears in Maxwell's equations, which describe the properties of electric and magnetic fields and electromagnetic radiation, and relate them to their sources.