答疑 如何求r? 3电流源及其特性曲线 I=s+lrl =IstU,/r Is+l2 Is+U/r △I=12-1 (U2-U1)/r =△U/r △U/△I答疑 3.电流源及其特性曲线 U I I IS S U I U I Ir IS r U I IS I1=IS+Ir1 =IS+U1 /r I2=IS+Ir2 =IS+U2 /r I= I2 -I1 =（ U2 - U1 ）/r = U/r r= U/ I 如何求r？