题目内容
等量正点电荷Q固定在如图所示的菱形长对角线两端,a、b为该菱形的短对角线端点,O为两对角线交点。下列措施中能让a点的电场强度等于零的有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242321079343774.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242321079343774.png)
A.在O点固定点电荷-Q/4 | B.在O点固定点电荷-4Q |
C.在b点固定点电荷-Q | D.在b点固定点电荷+Q |
AC
试题分析:设点a、b到正点电荷Q的距离为r,则两等量正点电荷Q分别在a点产生的场强
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824232109151600.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824232110555603.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824232111865724.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824232113222484.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824232114455391.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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