问题 选择题

如图甲所示,A、B为两个相同的环形线圈,共轴并靠近放置,A线圈中通过如图乙所示的电流I,则    

A.在t1到t2时间内A、B两线圈相吸引

B.在t2到t3时间内A、B两线圈相排斥

C.t1时刻两线圈作用力为零

D.t2时刻两线圈作用力最大

答案

ABC

题目分析:在t1到t2时间内,A中电流减少,穿过B的磁通量减少,根据楞次定律,则A、B两线圈相吸引;在t2到t3时间内,A中电流增大,A、B两线圈相排斥;t1时刻,A中电流最大,此时A中的电流的变化率为零,所以B中无感应电流产生,所以AB之间作用力为零;t2时刻,A中电流为零,此时A中的电流的变化率最大,在B中感应电流最大,AB之间作用力为零。选项ABC正确。

单项选择题
阅读理解

Mr. King lived with six hundred wild(野生)animals on the Greek Island of Kyklos. Ever since he left school, he had traveled all over the word collecting animals for his own zoo. He hoped to collect(收集) two examples of every kind of animal on his island(岛屿). But he was afraid that people would find him someday.

He wrote books about his travels and about his animals that he collected. The money from the books helped to pay for all the food that these animals ate.

One day, when Mr. King was out looking for drinking water, he found oil(石油). He needed money for his travels and for his zoo, and a little oil would buy enough water for what he needed all his life, but he knew that if he told anyone else about it, it would be the end of his zoo and his life’s work. So he decided not to tell anyone else about what he had found, because oil and water couldn’t mix.

小题1:.  . Mr. King traveled all over the world for collecting ______.

A.oil

B.water

C.animals

D.money小题2:.  . Mr. King was afraid that people would find him someday because ________.

A.he hadn’t got enough money for them

B.that would be the end of his zoo

C.he hadn’t got enough water and oil

D.they would buy his animals小题3:.  . Mr. King wrote books to _______.

A.tell people about his story

B.tell people how to find oil

C.get enough money for his animals

D.make money for his travels小题4:.  . In the passage, “oil and water couldn’t mix” means that “_________”.

A.Mr. King needed not only water but also oil

B.oil and water were rather difficult to be mixed together

C.Mr. King’s animals only needed water, not oil

D.if he told the others he found oil, his life’s work would be stopped