<Dd> The Electrostatic system of units (ESU) was based on Coulomb's quantification in 1783 of the force acting between two charged bodies . This relationship, now known as Coulomb's law can be written <Dl> <Dd> F e = k e q 1 q 2 r 2, (\ displaystyle F_ (\ mathrm (e)) = k_ (\ text (e)) (\ frac (q_ (1) q_ (2)) (r ^ (2))),) where k e = 1 4 π ε 0 (\ displaystyle k_ (\ text (e)) = (\ frac (1) (4 \ pi \ epsilon _ (0)))) (SI units) </Dd> </Dl> </Dd> <Dl> <Dd> F e = k e q 1 q 2 r 2, (\ displaystyle F_ (\ mathrm (e)) = k_ (\ text (e)) (\ frac (q_ (1) q_ (2)) (r ^ (2))),) where k e = 1 4 π ε 0 (\ displaystyle k_ (\ text (e)) = (\ frac (1) (4 \ pi \ epsilon _ (0)))) (SI units) </Dd> </Dl> <Dd> F e = k e q 1 q 2 r 2, (\ displaystyle F_ (\ mathrm (e)) = k_ (\ text (e)) (\ frac (q_ (1) q_ (2)) (r ^ (2))),) where k e = 1 4 π ε 0 (\ displaystyle k_ (\ text (e)) = (\ frac (1) (4 \ pi \ epsilon _ (0)))) (SI units) </Dd> <Dl> <Dd> In this system, the unit for charge is defined by setting the Coulomb force constant (k e (\ displaystyle k_ (\ text (e)))) to unity and the unit for electric potential was defined to ensure the unit of energy calculated by the relation E = Q V (\ displaystyle E = QV) is one erg . The electrostatic units of measure were the statampere, statvolt, and so on . </Dd> </Dl>

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