初中电学物理如图所示,电源电压不变.当纸只闭合开关S1且滑动变阻器R3接入电路电阻值最大时,电压表的示数为3.6V,滑动

P1=3.6*3.6/R1
P2=4.5*4.5/R2
P1/P2=8/1
R1/R2=6/5
R2=5R1/6
I1=E/(R1+R3)
I2=E/(R2+R3/2)
I1/I2= (2R2+R3)/ 2(R1+R3)
I1^2R3=1.44
I1R1=3.6
I2R2=4.5
I1R2/I2R2=[ (2R2+R3)/ 2(R1+R3)]*(6/5)=3.6/4.5
4R1+4R3=6R2+3R3
R3=6R2-4R1=6*5R1/6-4R1=R1
ER1/(R1+R2)=3.6
E=3.6*2=7.2V
P1=1.44W
R1=3.6*3.6/1.44=9Ω
R2=5R1/6=5*9/6=7.5Ω