ELECTRIC PERMITTIVITY OF VACUUM
The electrical constant is the proportionality coefficient in the Coulomb's law, which defines the force F of the interaction between two point electric charges q1 and q2 at distance r;
ε0 = (1/4π)·9·109 Ô/ì = 8,8542·10-12 Ô/ì.
The electrical constant, by analogy with the electric permittivity of medium, is also called electric permittivity of vacuum.