由串联电路中电流相等得:
P1/P2=81W/9w=9/1=I^2R1/I^2R2=R1/R2
再由串联电路中,各电阻两端的电压之比等于电阻的阻值之比得:
U1/U2=R1/R2=9/1
则有:
U/U1=(U1+U2)/U1=10/9.[注:U代表总电压,即电源电压]
所以有:
P1'/P1=(U^2/R1)/(U1^2/R1)=(U^2/R1)*(R1/U1^2)=U^2/U1^2=(U/U1)^2=(10/9)^2=100/81
即:P1'=100P1/81=100*81W/81=100W