题目内容
如图所示,平行板电容器的两个极板A、B分别接在电压为60 V的恒压电源上,两极板间距为3 cm,电容器带电荷量为6×10-8C,A极板接地.求:
(1)平行板电容器的电容;
(2)平行板电容器两板之间的电场强度;
(3)距B板为2 cm的C点处的电势.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241518447042057.jpg)
(1)平行板电容器的电容;
(2)平行板电容器两板之间的电场强度;
(3)距B板为2 cm的C点处的电势.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241518447042057.jpg)
(1)
(2)
,方向竖直向下 (3)-20 V
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151844735503.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151844985684.png)
试题分析:由电容器电容的定义式计算电容的大小,由匀强电场的场强与电势差的关系得到电场强度的大小,由电源极性判断场强方向,由A板接地的处C点的电势。
(1)由电容定义式可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241518451871154.png)
(2) 两板之间为匀强电场,由匀强电场的场强与电势差的关系有,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241518453121385.png)
(3)C点距A板间距离为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151845390756.png)
则A、C间电势差
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151845499850.png)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151845593610.png)
A极板接地所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151845671434.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151845811619.png)
点评:注意在用公式
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151845999592.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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