OE aH 对ggh a at H·d=I do E+B、Hl(H2+lH)l d(ee, ldx) dx dt OE HH+ dH =8-yldx at H oH OE dx ax at 图18-13 dt d H dl I e l   = +    对efgh: e f g h Hy Hy+ dHy dx l j 图18-1 x y z Hz Ey a b c d Ey Ey+ dEy dx l t H μ x E z o y   = −    Hz l-(Hz+dHz )l dt d(εEy ldx) = t E ε x Hz y   = −    ldx t E ε y   =