(2013•重庆模拟)如图所示,灯L1标有“6V 3W”字样,开关闭合后L1恰好正常发光,电流表A1的示数为1.5A,假设灯泡电阻不变,求:
(1)电源电压;
(2)L2的电阻;
(3)1min内电流对电路所做的功.