Coulomb’s law, or Coulomb’s inverse-square law is a law of physics that describes force interacting between static electrically charged particles. Consider two positive charges q1 and q2, separated by a distance r. the force interaction between the charges is directionally proportional to the magnitude of charges and the inversely proportional to the square of the distance between the two charges. It is mathematically expressed as…

where ke is Coulomb’s constant (ke = 8.9875×10^9 N m2 C−2), q1 and q2 are the signed magnitudes of the charges, and the scalar r is the distance between the charges. The force F of the interaction between the charges is attractive if the charges have opposite signs (i.e., F is negative) and repulsive if like-signed (i.e., F is positive).

Here the q1 and q2 is expressed by Coulombs.

r is in meter

Also, the above equation is written as

Here 4 * pi is the proportionality factor, € is permeability of air.