Two families of units are useful in the areas of electrostatics: the mks system and the system of cgs electrostatic units (esu). The electrostatic units will first be considered because of their historical significance and their simplicity.
If can be seen that there are two new concepts to be defined that have not previously been considered, namely, those represented by the electrostatic system to selected the concept represented by the symbols k and Q. it is most convenient in the electrostatic system to selected the concept represented by k as the one to be arbitrarily designated as fundamental (like length, mass, and time in mechanics). Then Q can be defined from Coulomb’s law. From this agreement, k is arbitrarily assigned the value of exactly. I dyn cm2 per unit charge2 for empty space. The esu of charge, usually called the statcoulomb (statiC), is defined as a point charge of such a magnitude that it is repelled by a force of one dyne if it is placed one centimeter away from an equal charge in empty space. The size of the statcoulomb makes it convenient for many problems in electrostatics.   _{Your Comment}