where ke is a constant called the Coulomb constant. In his experiments, Coulomb was
able to show that the value of the exponent of r was 2 to within an uncertainty of a few
percent. Modern experiments have shown that the exponent is 2 to within an uncertainty
of a few parts in 1016.
The value of the Coulomb constant depends on the choice of units. The SI unit of
charge is the coulomb (C). The Coulomb constant ke in SI units has the value
ke ! 8.987 5 & 109 N'm2/C2