题目内容
一平行板电容器充电后与电源断开,正极板接地,在两极板间有一带电油滴(电量很小,不影响电场分布)位于
点且恰好处于平衡状.如图所示,若保持正极板不动,将负极板移到图中虚线所示的位置,则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241532262641064.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153226170290.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241532262641064.png)
A.带电油滴将沿竖直方向向下运动 | B.![]() |
C.带电油滴的电势能不变 | D.电容器的电压增大 |
C
试题分析:充完电的电容器,与电源断开,则移动板时可以认为电荷量Q保持不变。通过
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153226513862.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153226638575.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241532268101054.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153226872877.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153227012547.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153227106564.png)
点评:这类问题的关键是看电键开关是否断开。若电键始终闭合,则说明电动势保持不变;若充好电之后电键断开,说明电容器电荷量保持不变。本题需要注意的地方是如何推导电容器间的电场。
![](http://thumb2018.1010pic.com/images/loading.gif)
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