问题
单项选择题
有一个额定值为220V、100W白炽灯，在正常使用时，其电流近似为（）。
A.A
B.B
C.C
D.D
答案
参考答案：A
解析：
已知白炽灯的额定功率为PN＝100W，额定电压为UN＝220V。
因为：PN＝UNlN所以额定电：
[点评] 掌握功率与电压、电流、电阻之间的关系，掌握欧姆定律。
本题如果求电阻R，则：
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有一个额定值为220V、100W白炽灯，在正常使用时，其电流近似为（）。
A.A
B.B
C.C
D.D
参考答案：A
解析：
已知白炽灯的额定功率为PN＝100W，额定电压为UN＝220V。
因为：PN＝UNlN所以额定电：
[点评] 掌握功率与电压、电流、电阻之间的关系，掌握欧姆定律。
本题如果求电阻R，则：
Jim is a boy who thinks a lot and learns a lot. One day when he was passing the elephants, he suddenly stopped. He saw a group of elephants and these big animals had a rope around their front . The rope was very , so the elephants could break it easily. But to his surprise, did not. Jim saw a trainer near the elephants. Then he walked over and asked him . “Well,” the trainer said, “When they were very young and much smaller , we used the same ropes to tie around their legs and, at that age, they were sure they hold(约束)them. As they get bigger and bigger, thy still believe the ropes can hold them, so they try to get away.” Jim thought a lot that. These animals could break their ropes at any time, but because they they couldn’t, they didn’t give it a try. Like the many of us believe that we can’t do something in our life, just because we didn’t do it successfully in the past.
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