Eight charges are arranged symmetrically on a circle of radius 0.4 m in air as shown. Their values are +5 μC, -7 μC, -5 μC, +7 μC, -5 μC, +11 μC, +7 μC and +15 μC. Find the electric potential at the centre O.

Question

G1 Physics · Accepted Answer

All eight charges are at the same distance r = 0.4 m from O, so potential is added algebraically. Net charge = (5 - 7 - 5 + 7 - 5 + 11 + 7 + 15) μC = 28 μC. Therefore V = (1/4πε₀)(Σq/r) = (9 × 10⁹)(28 × 10⁻⁶)/0.4 = 6.3 × 10⁵ V = 63 × 10⁴ V. Correct answer: A.