E·dS_q 分V·E=P/E0 F。dC=0 E·dC=0 U()-U(=Fde y-v(i E·dC E(r=-VV(r) Vo()= 1 p(r)dr 48 r 4 Eor-r V(∞)=00 0 / q E d S E     =    =  0 0 c c F d E d =   =   ( ) ( ) f i U f U i F d − = −   ( ) ( ) f i V f V i E d − = −   0 0 1 1 1 ( ) ( ) ( ) 4 4 | | ( ) 0 Q Q r dr V r V r r r r V      =  = −   =  E r V r ( ) ( ) = −