题目内容
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.闭合开关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/20140824/201408241450513512662.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241450513512662.png)
A.保持R1不变,缓慢增大R2时,F将变大 |
B.保持R1不变,缓慢增大R2时,F将变小 |
C.保持R2不变,缓慢增大R1时,F将变大 |
D.保持R2不变,缓慢增大R1时,F将变小 |
B
试题分析:保持R1不变,缓慢增大R2时,电路的总电阻增大,由闭合电路欧姆定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145051507612.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145051570452.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145051928545.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145052006479.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145051507612.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145051570452.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145051928545.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824145052006479.png)
点评:学生要知道含电容器的电路没有恒定电流,分析时按断路处理,本题的R1只起到导线的作用,没有和其他的元件构成回路。
![](http://thumb2018.1010pic.com/images/loading.gif)
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