半径为r的均匀带电球面1,带电量为q;其外有一同心的半径为R的均匀带电球面2,带电量为Q,则此-|||-两球面之间的电势差 _(1)-(U)_(2) 为 ()-|||-A. dfrac (q)(4pi {varepsilon )_(0)}(dfrac (1)(r)-dfrac (1)(R)) B. dfrac (Q)(4pi {varepsilon )_(0)}(dfrac (1)(R)-dfrac (1)(r)) C. dfrac (1)(4pi {varepsilon )_(0)}(dfrac (q)(r)-dfrac (Q)(R)) D. dfrac (q)(4pi {varepsilon )_(0)r}