问题 选择题
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

答案:A

阅读理解

Do you have a dictionary? I think almost everyone has one.But ,how often do you use a dictionary? I don't believe that everyone makes good use of it.You may come across lots of new words in your study and you will ask someone for the answers. But if you have a dictionary ,

please don't let it sleep.You should make better use of it .It can tell you not only the meaning of the words but also the use of them.What's more, it can tell you how to use them.

It is true that dictionaries are very useful and important to us.They are like silent teachers. When you have a question, you can turn to them.They will give you the right answer.They are also like a trusted friend and stay with you forever. You can learn a lot from them .

Don't be lazy. Don't let your dictionary sleep any more. You will find it is a new world if you walk to it.

小题1:Does everyone make good use of the dictionary?

A.No,they aren't.

B.No,they don't.

C.Yes,they do.

D.I don't know.小题2:What does a student often do if he comes across lots of new words in the study?

A.He will look them up in the dictionary.

B.He will ask his parents.

C.He will ask someone for the answers.

D.I don't know.小题3:What can a dictionary tell you?

A. The meaning of the words.               B. The use of the words.

C. How to use the words.                   D. A,B and C.

小题4:What are dictionaries like according to the passage?

A.They are like silent teachers and trusted friends.

B.They are of medium height.

C.They are very cute.

D.They are very beautiful.小题5:Which is TRUE according to the passage?

A.We should let the dictionary sleep.

B.Dictionaries are like our mothers.

C.Dictionaries are very useful to us.

D.We can see the film in the dictionary.

单项选择题