问题 问答题

AB两地间铺有通讯电缆,长为L,它是由两条并在一起彼此绝缘的均匀导线组成的,通常称为双线电缆。在一次事故中经检查断定是电缆上某处的绝缘保护层损坏,导致两导线之间漏电,相当于该处电缆的两导线之间接了一个电阻。检查人员经过下面的测量可以确定损坏处的位置:(1)令B端的双线断开,在A处测出双线两端间的电阻RA;(2)令A端的双线断开,在B处测出双线两端间的电阻RB;(3)在A端的双线间加一已知电压UA,在B端用内阻很大的电压表测出双线间的电压UB。

试由以上测量结果确定损坏处的位置。

答案

设双线电缆每单位长的电阻为,漏电处距A端为,漏电处的电阻为,则,由欧姆定律可知,解以上三式消去

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Jealous of the kids at school who are smarter than you and seem to learn more quickly? Don’t worry.  小题1: 

  小题2: However, according to a recent study, IQ can rise—not just by one or two points, but by as many as 21 points!

Scientists have found that IQ changes are linked to changes in part of the brain called gray matter, which was seen to grow and become denser(更加密集)in the brains of people whose IQs improved greatly.

  小题3: One is to train your short-term memory. Previous research has proven that short-term memory is the basis for intelligence, so trying to recognize or retell something that you have seen or heard can help raise your overall brain power.   小题4: 

A good night’s sleep will also help improve your concentration.  小题5: It helps you stay focused for longer the next day.

Scientists have also found that exercise helps. Walking 30 minutes a day five times a week and doing exercise will help you become more knowledgeable—as well as healthier and fitter.

A.There are several ways of increasing your brain’s gray matter.

B.Your brain deals more efficiently with things you truly like.

C.With a bit of brain training, the chances are that you can be as smart as they are.

D.So maybe it’s a good idea to get your brain in training right away.E. Getting enough sleep is like pushing the reset button in your brain.

F. The more you work on it, the better you will become.

G. People used to assume that a person’s IQ was unchangeable.

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