题目内容
平行板电容大路两极板之间距离为
在中央有一块带电网,网与正极板B之间的电势差为网与负极板A之间电势差的2倍,从板A与水平成
角飞出一个带正电粒子,最高到达B板
处,求粒子起飞到返回A上点之间的距离。(重力作用不计)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317061223856.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131705950395.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131705981310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706013395.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317061223856.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317062471020.png)
设粒子在板A与网之间运动的加速度为
,运动时间为
,在网与板B之间的加速度为
,运动时间为
,
令
则![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706527698.png)
且加速度![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706559903.png)
带电粒子从轨道最高点向下运动时有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706683759.png)
而由动能定理得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317067151268.png)
由于到最高点时原点的竖直分速度为0,故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706746865.png)
所以![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317068241224.png)
于是得水平距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317062471020.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706278313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706309385.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706387343.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706481416.png)
令
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706496463.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706527698.png)
且加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706559903.png)
带电粒子从轨道最高点向下运动时有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706683759.png)
而由动能定理得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317067151268.png)
由于到最高点时原点的竖直分速度为0,故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131706746865.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317068241224.png)
于是得水平距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241317062471020.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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