Electric Field due to a Point Charge

Let P be a point lying in vaccum at a distance r from a point charge q lying at O. Let a test charge q0 be place at P.

According to Coulomb’s law the force F acting on q0 due to q is

        F =     ___1___ qq0 r
           ____ 4П ε₀       r²

The direction of E is along the line joining O and P, pointing outward if q is positive and inward if q is negative.