啊发生大法师的法

(1) S1、S3断开，S2闭合时，R1,R2,R3串联, P1=U1²/(R1+R2)=6.4(2) 断开S1，闭合S2、S3时，R2,R3串联, P2=U2²/R2=8(3) 闭合S1，断开S2、S3时，R1,R2串联, I=E/(R1+R2)=1.6(1)--->U1²=6.4(R1+R2)；(2)--->U2²=8R2U1²:U2² = 6.4(R1+R2):8R2 = 16:9--->R1:R2=11:9设R1=11r，R2=9r--->电源电压E=30r(2)--->E/U2=(R2+R3)/R2(1)--->E/U1=(R1+R2+R3)/(R1+R2)--->E/U2:E/U1=U2:U1=(R2+R3)/R2:(R1+R2+R3)/(R1+R2)=4:3--->5(9r+R3)=3(20r+R3)--->R3=7.5r(2)--->P2=I²R2=[E/(R2+R3)]²R2=(64/33)²×9r=8--->r=8×(11/64)²=121/512--->E=32r=121/16 伏 R3=7.5r=1815/1024 欧