如图所示,第II象限中存在竖直向下的匀强电场，在ｘ轴的下方Ｌ处存在一个处置纸面向外的单边界匀强磁场。今有一个电量为+q、质量为m的粒子（不计重力）从A点
处以速度V0水平射入电场，恰好从坐标原点O处飞出，运动一段时间之后进入匀强磁场，并在磁场中经过P点（
）。求:
（1）平行板间的电场强度的大小；
（2）匀强磁场的磁感应强度的大小；
（3）粒子从A点运动到P点的时间。
(1) 
,(2) 
,(3) 
题目分析：（1）电场中，类平抛。
水平：
竖直：
且：
联立得：
（1分）
（2）飞出电场瞬间竖直速度
（2分）
粒子进入以450进入磁场，轨迹如图示。
由几何关系可得：
（2分）
因（2分）
(3)由（1）可知电场中运动时间：
（不计分）
出电场到磁场匀速直线运动用时：
（2分）
磁场中用时：
（2分）
总用时：（2分）
完形填空 (共20 小题；每小题1分；满分20分) 阅读下面短文, 掌握其大意, 然后从1---20各题所给的四个选项中,选出最佳选项. Seven loyal readers came to the Teens’ office two weeks ago. They had a wonderful day learning how to make a newspaper. But what 1 made them excited was that they had their say(发言权). "What most 2 me was when I was saying something, I found all eyes were on me," said Tang Shining, one of the students. Her friend, Li Chunbei 3 , and felt very glad that when she was talking, the editors nodded and 4 took notes. Students are happy to see the editors listen to their 5 . You may often 6 about being neglected（忽视） by teachers and parents. 7 before complaining please make sure that you have already spoken about your 8 . Traditionally in China, teachers at school and parents were 9 the ones to tell teenagers what they should and shouldn’t do. The young are 10 to doing what they are told, rather than thinking by themselves. But then their ideas would be locked in their brain and not be 11 . A girl wrote to Teens about her family story. She 12 to be very sad because her father seldom talked and played with her. After years of consideration, she 13 decided to write her father a letter, telling him about her sadness. To her 14 , the father 15 , saying that he didn’t realize his mistake. From then on, he really 16 . Sometimes, we need to let our 17 be heard, so others can understand our thoughts and feelings. Don’ t be afraid of being 18 for what you have done. You know it is your 19 to speak your mind. Even if your suggestions are denied, at least you have tried your best. You will not be left with any 20 .
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