例.平行板电容器:S>>d2 E oo g/s C AB=Ed gd g= 例.球形电容器: E=0 R E=0r≥R2 R E R<r<R 4兀Er 0 − 0 E  q =  S  0 例. 平行板电容器： d S C 0 0   = 0 0 0 /    q S  E = = 2 S  d S qd UAB Ed 0   = = 例. 球形电容器： R1 R2 o q o − q 0 R1 E = r   0 R2 E = r   2 1 2 0 0 ˆ 4 r R r R r q E =     