问题 问答题

如图所示,有两个同心导体圆环。内环中通有顺时针方向的电流,外环中原来无电流。当内环中电流逐渐增大时,外环中有无感应电流?方向如何?

 

答案

由于磁感线是闭合曲线,内环内部向里的磁感线条数和内环外向外的所有磁感线条数相等,所以外环所围面积内的总磁通向里、增大,所以外环中感应电流磁场的方向为向外,由安培定则,外环中感应电流方向为逆时针。

由于磁感线是闭合曲线,内环内部向里的磁感线条数和内环外向外的所有磁感线条数相等,所以外环所围面积内的总磁通向里、增大,所以外环中感应电流磁场的方向为向外,由安培定则,外环中感应电流方向为逆时针。

点评:本题要求考生掌握净磁通的概念,练习使用楞次定律的步骤。

选择题
阅读理解

阅读理解。

    One day a few years ago, a very funny thing happened to a neighbor of mine. He is a teacher at one of

London's big medical schools. He had finished his teaching for the summer term and was at the airport on

his way to Russia to give a lecture.

    He had put a few clothes and his lecture notes in his shoulder bag, and he had put Rupert, the skeleton

(人体骨架) to be used in his lecture, in a large brown suitcase. At the airport desk, he suddenly thought

that he had forgotten to buy a newspaper. He left his suitcase near the desk and went over to the shop.

    When he got back, he discovered that someone had taken his suitcase by mistake. He often wonders

what they said when they got home and found Rupert.

1. Who wrote the story? [ ]

A. Rupert's teacher.

B. The neighbor's teacher.

C. A medical school teacher.

D. The teacher's neighbor.

2. Why did the teacher put a skeleton in his suitcase? [ ]

A. He needed it for the summer term in London.

B. He needed it for the lecture he was going to give.

C. He wanted to take it to Russia for medical research.

D. He wanted to take it home as he had finished his teaching.

3. What happened at the airport? [ ]

A. The skeleton went missing.

B. The skeleton was stolen.

C. The teacher forgot his suitcase.

D. The teacher took the wrong suitcase.

4. Which of the following best tells the teacher's feeling about the incident? [ ]

A. He was angry.

B. He thinks it very funny.

C. He feels helpless without Rupert.

D. He feels good without Rupert.

5. Which of the following might have happened afterwards? [ ]

A. The teacher got back the suitcase but not Rupert.

B. The teacher got back neither the suitcase nor Rupert.

C. The teacher got back Rupert but not the suitcase.

D. The teacher got back both the suitcase and Rupert.