题目内容
如图所示, xoy平面内的正方形区域abcd,边长为L,oa=od=
,在该区域内有与y轴平行的匀强电场和垂直于平面的匀强磁场,一个带电粒子(不计重力)从原点沿+x轴进入场区,恰好沿+x轴直线射出。若撤去电场只保留磁场,其他条件不变,该粒子从cd边上距d点
处射出,若撤去磁场,只保留电场,其他条件不变,该粒子从哪条边上何处射出?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241242007582626.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200711234.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200727234.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241242007582626.jpg)
解:从原点沿x轴直线射出过程匀速直线运动,受力平衡:
①----------3分
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241242008204414.jpg)
当撤去电场,在匀强磁场中匀速圆周运动,如图所示,设半径为r
在
内有:
②----------3分
③----------3分
若撤去磁场,只保留电场,带电粒子向上偏转,做类平抛运动,设从f点射出:
④----------2分
⑤----------2分
⑥---------2分
由①②③④⑤式得:
⑦----------4分
该粒子从ab边射出,射出点距a点距离![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124201085465.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200773428.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241242008204414.jpg)
当撤去电场,在匀强磁场中匀速圆周运动,如图所示,设半径为r
在
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200836331.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200867676.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200883556.gif)
若撤去磁场,只保留电场,带电粒子向上偏转,做类平抛运动,设从f点射出:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200898453.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200914525.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124200992253.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412420100772.gif)
由①②③④⑤式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124201054504.gif)
该粒子从ab边射出,射出点距a点距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124201085465.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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