4、求电容电流 R τ=RC O au d t 解一: CUsd-er dt t>0 R 解二: LUs-U(I-er) R R R ic(t) e t>0 R4、求电容电流: 解一: (1 ) t S U e dt d C − = − , 0 t US e t R − = 解二: R U u i S C C − = [ (1 )] 1 t S S U U e R − = − − , 0 t US e t R − = t O iC =RC R US dt du i C C C =