场源电荷(+) E R 。r>R: P>R q/(4Sor) 4π80 r<R: q 2 < R 3 4 TCE 0 R 3 8πEnRR 2 R R: UD=0 入 R R.° Pr>R n 2 2T80 gce 0 R <R:0 < R 0 >R: R <R: UR=0 pR2-R OR 2 >R n=<0 28 0 28 0 入 28 0 r<R p (R 2π8 0 48 0 3场源电荷（+） E  U r  R: r r ˆ 2 0    r  R: 0  r  R r r R ˆ 0     UR = 0 r  R: R r ln 20  − r  R: 0 r  R r  R: r r ˆ 2 0    r  R:  r r R ˆ 2 0 2     r r ˆ 2 0    UR = 0 r  R: ln 0 2 0 2    r R R r  R: ( ) 4 2 2 0 R − r   q R r  r  R: r r q ˆ 4 2 0   r  R: r R qr ˆ 4 3 0   r  R: (4 ) 0 q  r r  R: R r R q (3 ) 8 2 2 0 −  3