问题 计算题

(18分)如图所示,相距为d、板间电压为U的平行金属板M、N间有垂直纸面向里、磁感应强度为B0的匀强磁场;在POy区域内有垂直纸面向外、磁感应强度为B的匀强磁场;POx区域为无场区.一正离子沿平行于金属板、垂直磁场射入两板间并做匀速直线运动,从H(0,a)点垂直y轴进入第Ⅰ象限.

(1)求离子在平行金属板间的运动速度;

(2)若离子经OP上某点离开磁场,最后垂直x轴离开第Ⅰ象限,求离子在第Ⅰ象限磁场区域的运动时间;

(3)要使离子一定能打在x轴上,则离子的荷质比应满足什么条件?

答案

(1)(2)(3)

题目分析:(1)粒子在平行板内做匀速直线运动,有,又

解得离子在平行板内的速度为:

(2)如图为离子在第一象限内的运动轨迹图,由几何关系可得,轨迹半径为

轨迹对应的圆心角为 ;运动的周期为:

运动时间为:

(3)要使粒子一定能打到x轴上,离子在磁场中运动的最小半径为r2,由几何关系

解得:

 可得:

阅读理解

阅读理解

Mr. White works in an office. One day, when he had lunch, a friend came to visit him . They were very happy and talked a lot. Then they looked at the clock on the wall. It was time to go to office. He had to say goodbye to his friend and left. It was raining hard and the streets were wet. He drove too fast to see the red lights . And he couldn’t stop his car and hit a car in front of his. An old man got off and called out angrily, “ What are you doing? Do you want to hit me to death?”

“I’m sorry , sir,” said Mr. White . “I didn’t find the lights turned red.” Then he brought out a bottle of wine and gave it to the old man .

“ It’s very cold today , sir ,” said Mr. white . “Please drink a little , then you’ll be warmer.” The old man drank some wine and became happy. “I’m feeling much better now. Why don’t you drink any?” he asked.

I can’t drink anything now ,sir,” answered Mr. White.

I’m waiting for the policeman to come. Only drunkards (酒鬼) cause accidents, you know!”

小题1: The story happened________________.

A.in the morning

B.in the afternoon

C.in the evening

D.at night小题2:Mr White drove too fast because _______________

A.he was happy that day

B.he was good at drinking

C.there were few cars in the street

D.he was afraid to be late小题3:Mr White hit the car because  ________.

A.he didn’t see it

B.it was raining hard

C.he couldn’t stop his in time

D.he couldn’t drive at all.小题4: Mr. White gave a bottle of wine to the old man ________.

A.to put the blame onto the old man

B.to make him happy

C.to make him warm

D.to leave there before the policeman小题5:At last ___________________.

A.the old man felt much better

B.the old man was friendly to Mr. White

C.Mr. White drank some ,too.

D.Mr. White fooled the old man .

单项选择题