Coulomb's constant, the electric force constant, or the electrostatic constant (denoted k e ) is a proportionality constant in equations relating electric variables and is exactly equal to k e = 8.9875517873681764×109 N·m2/C2 (m/F). It was named after the French physicist Charles-Augustin de Coulomb (1736–1806).
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Use of Coulomb's constant 
Coulomb's constant is used in many electric equations, although it is sometimes expressed as:
Some examples of use of Coulomb's constant are the following: