题目内容
如图,平行金属板中带电质点P原处于静止状态,不考虑电流表和电压表对电路的影响,当滑动变阻器R4的滑片向b端移动时,则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241654084795145.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241654084795145.jpg)
A.电压表读数减小 |
B.电流表读数减小 |
C.质点P将向上运动 |
D.R3上消耗 的功率逐渐增大 |
A
试题分析:由图可知,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408494361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408728347.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408931365.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165409352327.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408931365.png)
AB、当滑片向b移动时,滑动变阻器接入电阻减小,则电路中总电阻减小;由闭合电路欧姆定律可知,电路中总电流增大;路端电压减小,同时
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165409352327.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408931365.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408494361.png)
C、因电容器两端电压减小,故电荷受到的向上电场力减小,则重力大于电场力,电荷向下运动;错误
D、因
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408931365.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165411302606.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165408931365.png)
故选A
点评:动态问题分析思路总体来说是按照先部分后整体再部分的顺序,要充分利用电路中不变部分的电阻不变的特点,间接地讨论电路变化部分.还要注意电源是有内阻的。
![](http://thumb2018.1010pic.com/images/loading.gif)
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