To measure electrical quantities in SI the basic unit is entered — unit of current amps. Unit of charge in this system is derived and displayed from the formula

q=It. (14.6)

Units for charge are

q=1A*1C=1A*s=1Кл.

The SI unit of charge Coulomb is accepted (TC). The pendant is called electric charge, flowing through the cross section of the conductor at 1C with a current of 1A. The pendant is a very large unit of charge. It turns out, a charge of one Coulomb has 625*10¹⁶ protons (electrons). Measurements have shown, what:

e₊ = 1,60 *10^-19-TC, e_—=-1,60*10^-19 TC.

Unit ε_C the SI can be expressed as:

ε_C=q₁q₂/4πr²F=1 TC*1 TC/[4π*1 m2(1/4π)N]=1 KL²/(N*m²).

The SI unit for ε_C accepted dielectric constant of this medium, where two charges on each 1Кл, located at a distance of 1 m, interact with the force (1/4π)N.

Through experiments it was found the following value of the electric constant ε₀:

ε₀ = (1/36π *10⁹) TC²/ (N*m²) = 8,85*10^-12 TC²/(N*m²). (14.7)