Question: what is the magnitude of the electric force on q?
Answer: Using Coulomb's law, F=k∣q1q2∣r2 F = k ∣ q 1 q 2 ∣ r 2 , its magnitude is given by the equation F=k∣qQ∣r2 F = k ∣ q Q ∣ r 2 , for a point charge (a particle having a charge Q) acting on a test charge q at a distance r (see Figure 1).