原来很快乐
幼苗
共回答了24个问题采纳率:75% 举报
(1)当开关S1、S2都闭合时,R1与R2串联,电压表V1测电源的电压,电压表V2测R2两端的电压,
∵串联电路中各处的电流相等,且总电阻等于各分电阻之和,
∴
UV1
UV2=
I21(R1+R2)
I21R2=
R1+R2
R2=[5/3],
解得:R2=[3/2]R1;
(2)当开关S1闭合,S2断开时,电压表V1测电源的电压,电压表V2测R1、R2两端的电压之和,
U′V1
U′V2=
I22(R1+R2+R3)
I22(R2+R3)=
R1+R2+R3
R2+R3=
R1+
3
2R1+R3
3
2R1+R3=
5R1+2R3
3R1+2R3=[3/2],
解得:
R1
R3=[2/1],
∴
P1
P3=
I22R1
I22R3=
R1
R3=[2/1].
故选C.
1年前
4