34 R1∥R1+R,∥R2 R 11 R R R+Re =0.6A R R r+r 1.2A 所以 =1 0.64A I R R R I A I R R R I S S 1.2 0.6 2 3 3 2 1 4 4 1 = + = = + = (2) A R R R R u I S S 3 // // 1 4 2 3 = + = 所以 I = I1 − I2 = −0.6A + us - R4 R1 R3 I1 R2 I Is I2