题目内容
如图9所示,在竖直放置的光滑半圆形绝缘细管的圆心O处放一带负电的点电荷,将质量为
、带电量为
的小球从圆弧管的水平直径端点A由静止释放,小球沿细管滑到最低点B时,对管壁恰好无压力,则圆心处电荷在B点处的电场强度的大小为( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241355101843964.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135510075337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135510137330.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241355101843964.jpg)
A.![]() | B.![]() |
C.![]() | D.不能确定 |
C
由O点放的点电荷的电场线分布可知小球从A到B电场力不做功,
,在B点F-mg=
,F=3mg,C对;
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135510418784.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135510481582.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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A.![]() | B.![]() |
C.![]() | D.不能确定 |