11.由闭合电路欧姆定律(1)当U1=4V I1=0.5AR0=U1/I1=8欧（2）E=U1+I1R+I1r=4+0.5x6+0.5r E=I2R+I2r=6+r E=8v r=2欧12.S断开U=I1(R2+R3)=3VS闭合U‘=I2R2=2.88VE=U+(I1+U/R1)rE=U'+（I2+U'/R1)rE=3.6V r=1.2欧
第一个
第二个
