问题 选择题

关于通电导线所受安培力F的方向、磁感应强度B的方向和电流I的方向之间的关系,下列说法正确的是(   )

A.F、B、I三者总是互相垂直的

B.F总与B和I垂直,但B、I之间可以不垂直

C.B总与F和I垂直,但F、I之间可以不垂直

D.I总与F和B垂直,但F、B之间可以不垂直

答案

答案:B

据左手定则知安培力的方向一定垂直与电流方向,垂直与磁场方向。而电流和磁场方向可以成任意角度。B对。

判断题
阅读理解

阅读理解。

     After giving a talk at a high school, I was asked to pay a visit to a special student. An illness had kept the

boy home, but he was interested in meeting me. I was told it would mean a great deal to him, so I agreed.

     During the nine-mile drive to his home, I found out something about Matthew. He had muscular dystrophy

(肌肉萎缩症). When he was born, the doctor told his parents that he would not live to five, and then they

were told he would not make it to ten. Now he was thirteen. He wanted to meet me because I was a gold-medal

power lifter, and I knew about overcoming difficulties and going for my dreams.

     I spent over an hour talking to Matthew. Never once did he complain or ask, "Why me?" He spoke about

winning and succeeding and going for his dreams. Obviously, he knew what he was talking about. He didn't

mention that his classmates had made fun of him because he was different. He just talked about his hopes for

the future, and how one day he wanted to lift weights with me. When we had finished talking, I went to my

briefcase and pulled out the first gold medal I had won and put it around his neck. I told him he was more of

a winner and knew more about success and overcoming obstacles (困难) than I ever would. He looked at it

for a moment, then took it off and handed it back to me. He said, "You are a champion. You eamed that medal.

Someday when I get to the Olympics and win my own medal, I will show it to you."

     Last summer I received a letter from Matthew's parents telling me that Matthew had passed away. They

wanted me to have a letter he had written to me a few days before:

     Dear Dick,

     My mum said I should send you a thank-you letter for the picture you sent me. I also want to tet you know

that the doctors tell me that I don't have long time to live any more, but I still smile as much as I can.

     I told you someday that I would go to the Olympics and win, a gold medal, but I know now I will never get

to do that. However, I know I'm a champion, and God knows that too. When I get to Heaven, God will give

me my medal and when you get there, I will show it to you. Thank you for loving me.

                                                                                                                                        Your friend,

                                                                                                                                        Matthew

1. The boy looked forward to meeting the author because ____.

A. he was also good at weight lifting

B. he wanted to get to the Olympics and win a medal

C. he was one of the author's fans

D. he admired the author very much

2. From the underlined sentence in the third paragraph we can know the boy never complained about ____.

A. how unlucky he was to have this disease

B. not being able to go to school

C. why the author had never come to see him before

D. not getting a medal

3. From the passage we learn that ____.

A. Matthew was an athlete

B. Matthew had a positive attitude towards life

C. The author used to have the same disease as Matthew

D. Matthew became a champion before he died

4. Matthew didn't accept the author's medal because ____.

A. he thought it was too expensive

B. he was sure that he could win one in the future

C. he thought it was of no use to him as he would die soon

D. he would not be pitied by others

5. What would be the best title of this passage?

A. A Sick Boy

B. A Special Friend

C. A Real Champion

D. A Famous Athlete