(1)
外球壳上的电荷为零不变。
U2 = q / (4π ε0 R2)
(2)
接地后,U2 = 0.
设外球壳带电为 Q
U2 = q / (4π ε0 R2) + Q / (4π ε0 R2) = 0
得到 Q = - q
*(3)
内球壳接地,U1 = 0
U1 = = q' / (4π ε0 R1) + (- q) / (4π ε0 R2) = 0
q' = (R1/R2) q
U2 = = q' / (4π ε0 R2) + (- q) / (4π ε0 R2)
= q / (4π ε0 R2) * (R1/R2 - 1)