问题 选择题

如图所示,一个矩形线框从匀强磁场的上方自由落下,进入匀强磁场中,然后再从磁场中穿出,已知匀强磁场区域的宽度L大于线框的高度h,则下列说法正确的是

A.线框只在进入和穿出磁场的过程中,才有感应电流产生

B.线框从进入到穿出磁场的整个过程中,都有感应电流生

C.线框在进入和穿出磁场的过程中,都是机械能转化成电能

D.整个线框都在磁场中运动时,机械能转化成电能

答案

AC

题目分析:AB:只在进入和穿出磁场的过程中,线框的磁通量才发生变化,线框中才有感应电流产生;A正确B错误;C、由能量守恒可知,线框在进入和穿出磁场的过程中,都是机械能变成电能;正确

D、整个线框都在磁场中运动时,线框的磁通量不变,没有感应电流产生,机械能不变;错误;故选AC

点评:本题关键是,整个线框都在磁场中运动时,没有感应电流产生;在磁感应过程中能量是守恒的。

阅读理解

“Have a nice day!” may be a pleasant gesture or a meaningless expression. When my friend Maxie says “have a nice day” with a smile, I know she sincerely cares about what happens to me. I feel loved and secure since another person cares about me and wishes me well.

“Have a nice day. Next!” this version of the expression is spoken by a salesgirl at the supermarket who is rushing me and my groceries out of the door. The words come out in the same tone (腔调)with a fixed procedure. They are spoken at me, not to me. Obviously, the concern for my day and everyone else’s is the management’s attempt to increase business.

The expression is one of those behaviors that help people get along with each other. Sometimes it indicates the end of a meeting. As soon as you hear it, you know the meeting is at an end. Sometimes the expression saves us when we don’t know what to say. “oh, you just had a tooth out? I’m terribly sorry, but have a nice day.”

The expression can be pleasant. If a stranger says “Have a nice day!” to you, you may find it heart-warming because someone you don’t know has tried to be nice to you.

Although the use of the expression is an insincere, meaningless social custom at times, there is nothing wrong with the sentence except that it is a little uninteresting. The salesgirl, the waitress, the teacher, and all the countless others who speak it without thinking may not really care about my day. But in a strange and comfortable way, it’s nice to know they care enough to pretend they care when they really don’t care all that much. While the expression may not often be sincere, it is always spoken. The point is that people say it all the time when they like.

小题1:How does the author understand Maxie’s word?

A.Maxie shows her anxiety to the author.

B.Maxie really wishes the author a good day.

C.Maxie encourages the author to stay happy.

D.Maxie really worries about the author’s security.小题2:What does the underlined sentence in Paragraph 2 mean?

A.The salesgirl is rude.

B.The salesgirl is bored.

C.The salesgirl cares about me.

D.The salesgirl says the words as a routine.小题3:By saying “Have a nice day,” a stranger may______.

A.try to be polite to you

B.express respects to you

C.give his blessing to you

D.share his pleasure with you.小题4:According to the last paragraph, people say “Have a good day” __________

A.sincerely

B.as thanks

C.as a habit

D.encouragingly小题5:What is the best title of the passage?

A.Have a Nice Day---- a Social Custom

B.Have a Nice Day----- a pleasant Gesture

C.Have a Nice Day----- a heart-warming Greeting

D.Have a Nice Day----- a polite ending of a Conversation

问答题 简答题