题目内容
如图所示,M、N是平行板电容器的两个极板,R0为定值电阻,R1、R2为可调电阻,用绝缘细线将质量为m、带正电的小球悬于电容器内部.闭合电键S,小球静止时受到悬线的拉力为F.调节R1、R2,关于F的大小判断正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242137244751834.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242137244751834.png)
A.保持R1不变,缓慢增大![]() |
B.保持R1不变,缓慢增大![]() |
C.保持R2不变,缓慢增大![]() |
D.保持R2不变,缓慢增大![]() |
B
试题分析:当电路接通后,对小球受力分析:小球受重力、电场力和悬线的拉力F三个力的作用,其中重力为恒力,当电路稳定后,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213727782306.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213730590342.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213725489351.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213727782306.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213727782306.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213725489351.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824213730590342.png)
故选B
点评:解决本题的关键是1、熟悉含容电路的特点:电容两端间的电压与其并联部分的电压相等;含容支路中的电阻相当于导线.2、会正确的进行受力分析,搞清楚什么力变化导致拉力的变化.
![](http://thumb2018.1010pic.com/images/loading.gif)
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