题目内容
如图所示,有一带电量为+q的点电荷与均匀带电圆形薄板相距为2d,+q到带电薄板的垂线通过板的圆心.若图中a点处的电场强度为零,则下列说法正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241230597538466.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241230597538466.png)
A.圆形薄板带负电 |
B.图中b点的电场强度大小为![]() |
C.图中b点的电场强度大小为![]() |
D.图中b点的电场强度大小为0 |
B
图中a点处的电场强度为零,可知圆形薄板在a处的场强跟+q产生的场强平衡,大小为
,方向水平向右,根据对称性可知圆形薄板在b点产生的场强大小为
,方向水平向左,+q在b点产生的场强大小为
,方向水平向左,所以图中b点的电场强度大小为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123059816837.png)
故选B
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123059863599.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123059863599.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123059909954.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123059816837.png)
故选B
![](http://thumb2018.1010pic.com/images/loading.gif)
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