题目内容
在如图所示的电路中,R1、R3、R4均为定值电阻,R2是滑动变阻器,电流表内阻不计,电压表阻值很大,当R2的滑片向右滑动时,,电流表和电压表示数变化量的大小分别为DI、DU,下列结论正确的是 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241408377203844.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241408377203844.jpg)
A.电压表示数变大 | B.电流表示数变大 |
C.![]() | D.![]() |
AC
当滑动变阻器
的滑动触头P向右滑动时,
变大,并联电阻增大,回路总电阻增大,干路电流减小,电源电压降减小,路端电压增大,所以电压表示数变大,
组成的并联电阻增大,所以
两端的电压增大,
增大,同理
增大,则
减小,B项错误;
设回路总电流为
,由分析可知
,电压表测的是路端电压,电压表增大
,则电源内阻的电压减小
,由此可得![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838905169.png)
,结合上式得
<r,选项C正确。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140837844361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140837844361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140837922434.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140837985327.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838063293.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838141328.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838219323.png)
设回路总电流为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838297367.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838468578.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838546414.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838546414.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838905169.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140838952712.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140837735526.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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