P1:P2=9:8P=I²RI1²R1:I2²R2=9:8R1:R2=1:2代入上式I1:I2=3:2I1=0.3A I2=0.2AU1:U2=I1R1:I2R2=3:4P=UI 0.8=0.2U0 U0=4V R0=U0/I2=20欧I1(R1+R0)=I2(R2+R0)0.3(R1+20)=0.2(R2+20)R2=2R1R1=20欧R2=40欧U=0.3×(20+20)=12VR0先后功率比I1²R0:I2²R0=9:4所以选A
问一道中考物理题 2010河北物理类似问题答案