题目内容
(2010·海南物理·4)如右图, M、N和P是以
为直径的半圈弧上的三点,O点为半圆弧的圆心,
.电荷量相等、符号相反的两个点电荷分别置于M、N两点,这时O点电场强度的大小为
;若将N点处的点电荷移至P点,则O点的场场强大小变为
,
与
之比为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241409186391785.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918249513.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918295743.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918358351.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918405372.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918358351.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918405372.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241409186391785.png)
A.![]() | B.![]() | C.![]() | D.![]() |
B
依题意,每个点电荷在O点产生的场强为
,则当N点处的点电荷移至P点时,O点场强如图所示,合场强大小为
,则
,B正确。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241409192161250.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140918966454.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140919075574.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140919169605.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241409192161250.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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A.![]() | B.![]() | C.![]() | D.![]() |