如图所示，接于理想变压器中的三个规格相同的灯泡A、B、C都正常发光，试求：（1）理想变压器的原副线圈匝数比n1：n2为多少？
（2）若仅将B、C改为串联，输入电压U不变，则此时三个灯泡的功率之比多大？
（1）由于三个灯泡均正常发光，所以变压器的输出电流I2与输入电流I1之比为2：1
则有：
=n1 n2
=2：1I2 I1
（2）当B、C串联时，流过它们的电流相等，它们的功率之比为：PB=PC
此时流过B、C的电流等于变压器的输出电流
，流过A的电流等于变压器的输入电流I ′2
，I ′1
所以：
：I ′2
=2：1 I ′1
故A、B灯泡的功率之比：PA：PB=1：4，
所以三个灯泡的功率之比为：PA：PB：PC=1；4：4．
(2013·高考陕西卷)To celebrate the end of our exams，my friends and I went to a fast food restaurant.We____hamburgers and Coca Cola at the counter.When our____came，I started walking towards an empty table.By bad luck，my purse strap(带子)got____on a chair and the tray(托盘)that I was holding slipped___my hands and went flying in the air.The tray，and its contents，____on a man who was just about to____a bite of his sandwich.I stared，greatly____，as the drinks soaked(浸湿)his white shirt. Then I___my eyes and prepared myself for his burst of____.Instead，he said“It’s OK”to____me before he disappeared into the washroom. Still shaky and unsure____to do next，my friends and I went to a table and sat there，trying our best to look____.A moment later，the man came out of the washroom and___our table.My heart almost stopped____.I thought he was going to ask for my father’s__and call him. To my surprise，he merely smiled at us，handed us some cash and said，“____yourself new hamburgers.”He then walked____without even finishing his food. He could have made what was already an uncomfortable situation worse，____he chose a different way and gave us a reason to believe that there is still____in this world.I’ll never____his actions.
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