题目内容
在场强为E的匀强电场中,放一个电量为Q的点电荷,并以它为圆心在平行于电场线的平面内做一个圆。过圆心的电场线和圆交于A、B两点,A、B的垂直平分线交圆于C、D,如右图所示。A点的电场强度是零。电荷带 电,圆的半径R= ,B点的合场强大小是 ,C点的合场强大小是 。
、负、
、2E、![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838980454.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838917642.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838980454.png)
因为A点电场强度为零,所以可知点电荷的电场与匀强电场合场强为零,即可判断A处场强方向指向点电荷Q,则说明电荷带负电,因为
,所以可知圆的半径R=
,B点的合场强大小是
,因为ABC在同一圆周上,所以各点电场强度大小相等,则C点的合场强大小是![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124839479668.png)
故答案为:负、
、2E、![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838980454.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124839058697.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838917642.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124839151817.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124839479668.png)
故答案为:负、
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838917642.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124838980454.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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