问题 选择题

如图11所示是一种延时开关,当S1闭合时,电磁铁F将衔铁D吸下,C线路接通。当S1断开时,由于电磁感应作用,D将延迟一段时间才被释放。则(     )

A.由于A线圈的电磁感应作用,才产生延时释放D的作用

B.由于B线圈的电磁感应作用,才产生延时释放D的作用

C.如果断开B线圈的电键S2,无延时作用

D.如果断开B线圈的电键S2,延时将变长

答案

BC

A线圈有电流通过,使F产生磁场使得D被F吸下,这是显然。当S1断开时,励磁电流消失,此时磁场强度减小,A,B线圈中穿过的磁感线数目均发生变化,由于A线圈已经断开,在其中不产生感应电流,对磁场强度的减小没有抑制作用;而B线圈中产生感应电流,该电流产生的磁场抑制F中原磁场的减弱,这即是延迟效应产生的原因。当然,S2断开的话线圈B也不产生感生电流,不会对F中磁场的减弱产生阻碍。BC正确。故本题选BC。

单项选择题 共用题干题
阅读理解

There is no doubt that much of the profit of a business—sometimes the whole of its success—depends upon the use of the odds and ends.The odds and ends are various small things,which are left over when the main things are produced.But they possess a real value of their own.

If a business,big or small,looked down upon these odds and ends,it would mean a big difference in the amount of the benefit of the business.Take a meat factory for instance, there are countless odds and ends—bones and hair,which can be made into glue and rope to increase its profit greatly.

Then,if we are college students,what about our odds and ends—the odd moments? Take time for example.Every one of us has the exact same amount of it.Everyone’s success or failure depends on the use of their time.But everyone uses the time more or less in the same way.However,why many great men in science or art have made huge successes for themselves in the world?Because they have made best use of their odd moments.Take Thomas A.Edison, he never allowed his odd moments to slip by.He thought,planned,and tried his inventions.He always worked twenty hours out of each twenty-four.His inventions made him famous all over the world,and provided valuable wealth for the human beings.

So, remember this axiom:very busy people always find time for everything.However,people with great spare time find time for nothing.Is it very strange?Not at all!The question is how to gather up fragments of time and make full use of them.As many big businesses have found,that the real profit is in using the odds and ends.We also must do in this way to make best use of our odd moments and manage to be successful in something that we do.

小题1: What are odds and ends?

A.They are nothing useful.

B.They are various small,but valuable things.

C.They are the main things that factories produce.

D.They are odd moments students deny to gather up.小题2: Why should the odds and ends be made full use of ?Because  ____   .

A.lots of factors in success or in failure depend on the best use of odds and ends

B.they control to possess a value of their own

C.they are various small things people don’t want

D.they are useless things left over when the main things are produced小题3:What does the word “Axiom” in the fourth paragraph mean?

A.clear and evident without proof

B.statement accepted as true without proof of argument

C.statement that can be argued

D.regulation accepted in scientific usage小题4: “Fragments of time” equals  “____   ”in the above passage.

A.the odds and ends

B.immense leisure

C.the main things

D.the odd moments