試題詳解

12. A series of 3 uncharged concentric spherical conducting shells surround a small central charge q. The potential at a point outside the third shell, at distance r from the center, and relative to V = 0 at ∞, is
(A) −3keq/r
(B) +3keq/r
(C) − (ln 3)keq/r
(D) + (ln 3)keq/r
(E) +keq/r