题目内容
在如图所示的电路中,E为电源电动势,r为电源内阻,R1和R3均为定值电阻,R2为滑动变阻器.当R2的滑动触点在a端时合上开关S,此时三个电表A1、A2和V的示数分别为I1、I2和U.现将R2的滑动触点向b端移动,则三个电表示数的变化情况是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241650287993342.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241650287993342.png)
A.I1增大,I2不变,U增大 | B.I1减小,I2增大,U减小 |
C.I1增大,I2减小,U增大 | D.I1减小,I2不变,U减小 |
B
试题分析:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029173361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029173361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029626365.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029891327.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029173361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029891327.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165030999292.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165031467338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165029173361.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165032013324.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165032325354.png)
故选B.
点评:解决本题的关键抓住电动势和内电阻不变,结合闭合电路欧姆定律求解.注意做题前一定要理清电路,看电压表测的是什么电压,电流表测的是什么电流.
![](http://thumb2018.1010pic.com/images/loading.gif)
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