1恒定电流的电场 U=p=RN=g《CA Ba-g0-as列 E△1：n= A7d E.n=j.n ·对任意n成立，故j=oE 81 恒定电流的电场  对任意 成立，故 (J S ) S l U R I       =  =  =   (J S n) S l E l           =  S J n S l E l n            =  E n J n      =   1 n  J E   =  8