题干

一个标有“220V  1100W”的电炉,正常工作时电阻丝的电阻有多大?假如电路中的电压降低到198V,电阻丝的电阻不变,这时电炉实际的电功率有多大?

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答案(点此获取答案解析)

【解答】解:
已知电炉的额定电压和额定功率,
由P=
U
2
R
可得电阻丝的电阻:

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阅读理解

    Have you thought about what determines the way we are as we grow up? Remember the TV program Seven Up! It started following the lives of a group of children in 1963. We first meet them as wide-eyed seven-year-olds and then catch up with them at seven-year intervals (间隔): nervous 14-year-olds, serious 21-year-olds, then grown-ups.

    Some of the stories are inspiring, others sad, but what is interesting in almost all the cases is the way in which the children's early hopes and dreams are shown in their future lives, for example, at seven, Tony is a lively child who says he wants to become a sportsman or a taxi driver. When he grows up, he goes on to do both. Nicki says, “I'd like to find out about the moon.” and goes on to become a space scientist. As a child, soft-spoken Bruce says he wants to help “poor children” and ends up teaching in India.

    But if the lives of all the children had followed this pattern, the program would be far less interesting than it actually was. It was the children whose childhood did not prepare them for what was to come that made the program so inspiring. Where did their ideas come from about what they wanted to do when they grew up? Are children influenced by what their parents do, by what they see on television, or by what their teachers say? How great is the effect of a single important event? Many film directors, including Stephen Spielberg, say that an early visit to the cinema was the turning point in their lives. Dr Magaret Me Allister, who has done a lot of research in this area, thinks that the major influences are parents, friends and the wider society.