Why use k = 1/[4(pi)(epislon)] and epsilon = 8.8 * 10^(-12) and subsequently, k = 9 * 10^9 It could simply be k = 9 * 10^9, and different k for different medium instead of different permittivity for different medium. What I mean is why does Pi, (I can handle the 4) comes into the equation, one reason I can think of is that it comes if you use Gauss Law to derive Coulomb's law but I am looking for something more convincing. The Permittivity of free space is a constant experimentally derived. Why would one derive that in the first place? If the force between two charges was directly proportional to some constant K. One would experimentally see that it is 9 * 10^9. Where was the idea of breaking it down to 1/[4(pi)(epislon)] entertained?