R与L串联
灯L正常发光,则I=P/U=3W/6V=0.5A
U1=U-U2=9V-6V=3V
R=U1/I=3V/0.5A=6欧
P1=U1I=3V*0.5A=1.5W 此时灯P2=P额=3W
p2/p1=3W/1.5W=2