题目内容
如图所示,长为L(L=ab=dc),高为L(L=bc=ad)的矩形区域abcd内存在着匀强电场。电量为q、质量为m、初速度为
的带电粒子从a点沿ab方向进入电场,不计粒子重力。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458257021190.png)
(1)若粒子从c点离开电场,求电场强度的大小
(2)若粒子从bc边某处离开电场时速度为
,求电场强度的大小
(3) 若粒子从cd边某处离开电场时速度为
,求电场强度的大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825640325.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458257021190.png)
(1)若粒子从c点离开电场,求电场强度的大小
(2)若粒子从bc边某处离开电场时速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825749265.png)
(3) 若粒子从cd边某处离开电场时速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825749265.png)
(1)
(2)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458261231041.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825936878.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458260141044.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458261231041.png)
试题分析:(1)a→c过程粒子类平抛 沿
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825640325.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145826326465.png)
垂直
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825640325.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145826654625.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145826716684.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825936878.png)
(2)离开电场时垂直
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145825640325.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145827153622.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145827246169.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458273091011.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458260141044.png)
(3)由动能定理
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145827512982.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241458261231041.png)
点评:做此类问题的关键是找出粒子在各个方向上的运动,然后结合牛顿定律以及动能定理解题
![](http://thumb2018.1010pic.com/images/loading.gif)
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