Question

如图23所示电路，断开开关S3,只闭合S1时，电阻R1消耗的功率为P1，断开S3，只闭合S2时，

如图23所示电路，断开开关S3,只闭合S1时，电阻R1消耗的功率为P1，断开S3，只闭合S2时， 宝宝57368 | 2010-12-18 | 分享 问题补充：电阻R2消耗的功率为P2，已知P1：P2=4:3，R1=3R2，开关都闭合时，电路消耗的总功率为64W，求 （1）电阻R2：R3为多少？ （2）当断开S3，只闭合S2时，电阻R3消耗的电功率是多少？

Answer 1

P1=[U/(R1+R3)]^2R1
P2=[U/(R2+R3)]^2R2
R1=3R2,P1:P2=4:3=(R2+R3)^2R1/[R1+R3)^2R2]=3(R2+R3)^2/(3R2+R3)^2
(R2+R3)^2/(3R2+R3)^2=4/9
(R2+R3)/(3R2+R3)=2/3
R3=3R2=R1,R2:R3=1:3

P=64W=U^2/[R1R2/(R1+R2)]=4U^2/(3R2),U^2=64*3R2/4=48R2
P3=[U/(R2+R3)]^2R3=U^2R3/(R2+R3)^2=48R2*3R2/(R2+3R2)^2=9W