1、W=100r/(2000r/kwh)=0.05kwh,P=3min=0.05h

实际功率P=W/t=0.05kwh/0.05h=1kw=1000w

2、U1=U-U2=12V-4V=8V

通过灯泡L1电流I=U1/R1=8V/8Ω=1A