问题 选择题

如图所示,匀强磁场垂直于yOz平面竖直向上,要使速率相同的电子进入磁场后,受到的洛伦兹力最大,并且方向指向y轴正方向,那么电子运动方向可能是(   )

A.沿z轴正方向进入磁场

B.沿y轴正方向进入磁场

C.在yOz平面内,沿任何方向进入磁场

D.在xOz平面内,沿z轴负方向射入磁场

答案

答案:D

A项洛伦兹力沿y轴负方向,B项洛伦兹力沿z轴负方向,故A、B错误.在yOz平面内,沿任何方向进入磁场的电子,虽然都满足洛伦兹力最大,但不能使洛伦兹力沿y轴正方向,C错.在xOz平面内,沿任何方向进入磁场的电子,都能满足洛伦兹力最大,只要电子沿z轴负方向射入,就能使洛伦兹力方向沿y轴正方向,D正确.

单项选择题 A1型题
完形填空

SECTION B(18 points)

Directions: For each blank in the following passage there are four words or phrases marked A,B,C and D.Fill in each blank with word or phrases that best fits the context.

Those days I’ve prepared to complete my college degree. The last project was named “smile”, which required us to go out and smile at three people and   36   their reactions.

It was freezing. My friend and I went out to a fast food restaurant. We were standing in line, waiting to be   37  , when all of a sudden people around us began to back away from their position.

As I   38  I smelt a terrible “dirty body” smell, and there standing behind me were two poor homeless men. As I looked down at the short gentleman close to me, he was smiling and his nice sky – blue eyes searched for   39  .

To sit in the restaurant and   40  up, they had to buy something. When the young casher at the counter asked what they wanted to order, one of them said coffee because that was all they could   41  . I smiled and asked the casher for two more breakfast meals on two   42  plates. Then I walked around the corner to the table that the men had chosen as a resting spot. I put the plates on the table and   43   the blue – eyed little man’s cold hands with my hands. With tears in his eyes, he said. “Thank you”. I noticed that all the   44  in the restaurant were set on me at that time.

I returned to college and   45   a paper about this story as my project to the instructor. She read it and though highly of my project. Just then I realized in my own way I had   46   the people at the restaurant, my friend, the instructor, and every person that shared the classroom. I graduated with one of the biggest lessons I would ever learn unconditional acceptance.

Much love and compassion is sent to each person who may read this and learn how to   47  people.

36.A.recognize  B.record         C.describe       D.imagine

37.A.paid     B.treated         C.served         D.charged

38.A.turn up     B.turn down     C.turn to         D.turned around

39.A.assistance  B.acceptance       C.advice         D.admission

40.A.break          B.pick         C.cheer         D.warm

41.A.afford      B.enjoy          C.spend          D.drink

42.A.big       B.separate       C.beautiful      D.special

43.A.shook       B.shared         C.clapped        D.covered

44.A.customers B.hands          C.eyes         D.sounds

45.A.handed in B.wrote down      C.took out       D.search for

46.A.involved   B.contacted     C.investigated      D.touched

47.A.hate     B.please          C.love         D.beat