## College Physics (4th Edition)

We can find a general expression for the electric potential at a point: $V = \frac{k~Q}{r_1}+\frac{k~Q}{r_2}-\frac{k~Q}{r_3}-\frac{k~Q}{r_4}$ At points A, B, and C: $r_1 = r_3$ and $r_2 = r_4$ Then $V = 0$ At point D: $r_1 \lt r_3$ and $r_2 \lt r_4$ Then $V \gt 0$ At point E: $r_1 \gt r_3$ and $r_2 \gt r_4$ Then $V \lt 0$ The correct answer is: (c) A, B, and C