Vacuum permittivity
F/m
A measure of how much electric field lines 'spread out' in vacuum — it sets the strength of electric forces and appears in Coulomb's law. Together with the vacuum permeability it determines the speed of light: c² = 1/(ε₀μ₀).
Used in
- Coulomb's law F = q₁q₂/(4πε₀r²)
- Capacitance calculations
- Deriving the speed of light
Source: SI defining constants / CODATA 2018