Explanation (1) the force acts along the line joining the two charges, (in the direction r1) (2)the force is o the product QaQb, so the force is repulsive if @a&@b are of the same sign attractive if @a&@b are of the different sign (3 the force x r, important.(what if not Unit: (in SI Unit System) ab- newton; @a Qb-coulomb; r--meter