試題詳解

12. A non-conducting sphere of radius R has a total charge Q spread uniformly throughout its volume. What is the potential energy U of the sphere?k = Coulomb-law constant)
(A) kQ²/R；
(B)kQ²/2R；
(C) 3kQ^2/2R；
(D) 3kQ²/4R；
(E) 3kQ²/5R.