Potential energy of point-charges: Two equal positive charges are held in place at a fixed distance. If you put a third positive charge midway between these two charges, its electrical potential energy of the system (relative to infinity) is zero because the electrical forces on the third charge due to the two fixed charges just balance each other.

Question

Quizplus · Accepted Answer

The electrical potential energy of the system is not zero. While the forces on the third charge from the two other charges may balance out, resulting in no net force, the potential energy is determined by the positions of the charges relative to each other. Each pair of charges contributes positively to the total potential energy of the system, so with three positive charges, the system has positive potential energy.

Potential Energy of Point-Charges: Two Equal Positive Charges Are Held