Consider a positive charge +q due to which the intensity of the electric field at a point P is to be calculated.
To find the intensity of electric field at point P, consider the positive test charge qₒ situated at that point.
Therefore,
Electric force on positive test charge qₒ
F = [1/4π€₀].[q.q₀/r²] Newton
Electric field intensity at a point P,
E=F/qₒ
F = E.qₒ
E.qₒ = [1/4π€₀].[q.q₀/r²]
E = [1/4π€₀].[q/r²] N/C