6v,3w灯泡电阻 R1=U^2/P1=36/3=12欧 ，6v,3w灯泡电阻 R2=U^2/P2=36/6=6欧 串联 l1正常发光，电流强度 I1=P1/U1=3/6=0.5A l2两端电压 U2=I1R2=3V 实际功率 P2=I1U2=1.5w 电源电压 U=U1+U2=6+3=9V
