如图所示,标有“5V 5W”字样的小灯泡L与电阻R串联在电路中,电源电压为8V.当开关S闭合时,小灯泡恰好正

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  • 5;3

    (1)灯泡正常发光时的电阻R=

    =

    =5Ω;

    (2)灯泡正常发光时的电流I=

    =

    =1A,

    电阻R两端的电压U R=U﹣U L=8V﹣5V=3V,

    电阻消耗的功率P=UI=3A×1A=3W