① 断开R5电阻,则开路电压: Uabo = - I2 * R2 + I1 * R1 = 15 V
其中:I1 = U / (R1 + R3) = 15 / (3 + 5) = 15/8 A
I2 = U / (R2 + R4) = 15 / (6 + 20) = 15/26 A
② 除源的等效内阻(电压源短路):
Rabo = (R2//R4) + (R1//R3) = 6//20 + 3//5 = 675/104 Ω ≈ 6.5 Ω
③ I5 = Uabo / (Rabo + R5) = 15 / (675/104 + 1.5) = 1.8773 A
也可以近似为 = 15 / (6.5 + 1.5) = 15/8 A