q = charge (Coulombs, C)
r = distance between charges (m)
ε 0 = permittivity of space or vacuum
The quantity of charge (number of electrons) is measured in the unit Coulomb - C - where
1 coulomb (C) = 6.24 10 18 electrons
The smallest charge that exists is the charge carried by an electron equal to -1.602 10 -19 coulomb .
Two spheres in air with distance 20 mm is both charged with 2 μC (2 10 -6 C) . The force acting between the two spheres can be calculated as
F = ( 8.98755 10 9 Nm 2 /C 2 ) ( (2 μC ) (10 -6 C/ μC )) ( (2 μC ) (10 -6 C/ μC )) / ((20 mm)(10 -3 m/mm)) 2
= 90 N
Electrical units, amps and electrical wiring, wire gauge and AWG, electrical formulas and motors.
Common materials and their relative permittivity.
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