问题 选择题

如图12-2所示,把一个闭合线圈放在蹄形磁铁两磁极之间(两磁极间磁场可视为匀强磁场),蹄形磁铁和闭合线圈都可以绕OO′轴转动.当蹄形磁铁匀速转动时,线圈也开始转动,当线圈的转动稳定后,有(  )

图12-2

A.线圈与蹄形磁铁的转动方向相同

B.线圈与蹄形磁铁的转动方向相反

C.线圈中产生交流电

D.线圈中产生为大小改变、方向不变的电流

答案

AC

本题考查法拉第电磁感应定律、楞次定律等考点.根据楞次定律的推广含义可知A正确、B错误;最终达到稳定状态时磁铁比线圈的转速大,则磁铁相对线圈中心轴做匀速圆周运动,所以产生的电流为交流电.

阅读理解

At times my mom has been uncomfortable seeing these qualities in me. For example, when I was 12, I went to Puerto Rico all by myself to stay with my grandmother for the summer. My mom was extremely nervous about it. She kept telling me how things were different in Puerto Rico, to always put on sunscreen, not to wander away from my grandmother, and other warnings. She helped me pack and did not leave the airport until she saw my plane take off.

But despite her worries, she let me go on my own. As I moved into my teens, she continued to give me space to grow and learn, even when it might have been difficult for her. When I reached my senior year, I decided to move away for college. Once again I found that I differed from my peers. While many of them wanted to stay close to home, I couldn't wait to be out in the world on my own. I had been looking forward to this chance for longer than I could remember. And once again, while my mom may not have been happy at the thought of me going away, she was supportive and excited for me. Sure, there were times when she’d nag (不断地唠叨)me about certain choices I made, but for the most part she did not stand in my way.

One big thing I realized during my senior year was that she actually believes in me and trusts me. That means a lot. Most of my life, and especially when I was little, the main person I tried to impress was my mother. I knew she expected nothing but the best from me. Sometimes it was hard to live up to her standards; getting a single B on my report card would make me feel bad because I knew she wanted me to have all A’s.

I know that her high standards have helped me stay focused on what's important, like education, and made me who I am. I am thankful for her support and involvement in my life. Most of all I respect her; she is the strongest woman I know and that's why I have turned out so strong and independent.

小题1:When the author decided to go to Puerto Rico, his mother ________.

A.wanted to go with him

B.worried about his safety

C.didn’t allow him to go

D.asked his grandmother for advice小题2:The author decided to move away for college to ________.

A.be different from his peers

B.keep away from his mother

C.be independent in outside world

D.make his mother unhappy小题3:We can learn from the third paragraph that the author’s mother ________.

A.had a high expectation from him

B.was too strict with him

C.used to expect nothing from him

D.cared little about his learning小题4:We can learn from the last paragraph that the author ________.

A.is quite grateful for his mother’s trust

B.still doesn’t quite understand his mother’s attitude

C.doesn’t like his mother’s involvement in his life

D.wishes to have more freedom from his mother

单项选择题