如图所示的电路中，电源的电动势E=12V，内阻未知，R1=8Ω，R2=1.5Ω，L为规格“3V，3W”的灯泡，开关S断开时，灯泡恰好正常发光。（不考虑温度对灯泡电阻的影响）试求：
（1）灯泡的额定电流和和灯丝电阻；
（2）电源的内阻；
（3）开关S闭合时，灯泡实际消耗的功率。
解：（1）灯泡的额定电流
灯丝电阻
（2）断开S时，灯L正常发光，即I1=I0，根据闭合电路欧姆定律
得
（3）闭合S时，设外电路总电阻为R外
设干路电流为I总，
灯两端的电压UL，
灯的实际功率PL，
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| My father has smoked for over twenty years. One evening,I asked my father 1 he couldn't quit smoking. He explained that he had 2 to quit several times before but he failed.I didn't want my father to get sick or die; 3 that night I begged him to try to quit one more time. He agreed. He 4 all of his cigarettes away in the garbage (垃圾) outside. The next day,my father and I 5 early to go fishing. As we drove out of the town,I noticed that Dad was more worried than usual .I forgot what it was, but I did something that made Dad 6 with me. He shouted at me, which is something he 7 did! I was so frightened that I started crying. Dad came over and told me how sorry he was. It was because of the 8 , he said. He just had to have one! We.got back in the car and 9 to the nearest country store quickly. Dad ran in and a moment later came out with a 10 of cigarettes. At last,l wasn't able to help Dad quit smoking,either. | ||||
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