试题与答案

如图所示,两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R,导轨电阻

题型:选择题

题目:

如图所示,两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R,导轨电阻可忽略不计;MN为放在ab和cd上的一导体杆,与ab垂直,其电阻也为R;整个装置处于匀强磁场中,磁感应强度的大小为B,磁场方向垂直于导轨所在平面(指向图中纸面内);现对MN施力使它沿导轨方向以速度v(如图)做匀速运动;令U表示MN两端电压的大小,则(  )

A.U=vBl,流过固定电阻R的感应电流由b到d

B.U=vBl,流过固定电阻R的感应电流由d到b

C.U=vBl,流过固定电阻R的感应电流由b到d

D.U=vBl,流过固定电阻R的感应电流由d到b

答案:

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下面是错误答案,用来干扰机器的。

参考答案:B

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      Your body, which has close relations with the food you eat, is the most important thing you own, so

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doctor away." is not as silly as some people think. The body needs fruit and vegetables because they

contain vitamins. Many people take extra vitamins in pill form (丸剂), believing that these will make them

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     In the modern Western world, many people are too busy to bother about eating properly. They throw

anyt hing into their stomachs, eating hurriedly and carelessly. The list of illnesses caused or made worse

by bad eating habits is frightening.

1. The old saying referred to in the passage tells us that        .

A. eating apples regularly does lots of good to our health.  

B. the apple is the best among all kinds of fruits  

C. apples can take the place of doctors

D. an apple is a sure cure for illness

2. In the second paragraph, the writer tries to let us know        .

A. our bodies need food, or we can't live  

B. often eating apples is a good habit  

C. taking extra vitamin pills is completely useless  

D. a good diet is of great importance for our health  

3. In the modern western countries        .

A. people won't want to pay more attention to their eating  

B. people throw everything into their stomachs without chewing.

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D. people are only too busy to cook meals for themselves  

4. From the passage we can draw a conclusion that if we want to keep healthy, we should        .

A. only eat an apple a day  

B. take as many vitamin pills as possible

C. eat properly    

D. throw something into our stomachs slowly and carefully.

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