题目内容
如图所示,电源的电动势为E,内电阻为r,外电路接有定值电阻
和滑动变阻器R,合上开关S,当滑动变阻器的滑动片P从R的最左端移到最右端的过程中,下述说法正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250037285545989.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003728523327.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250037285545989.png)
A.电压表读数一定变大 | B.电压表读数一定变小 |
C.R消耗的功率一定变大 | D.R消耗的功率一定变小 |
A
试题分析:滑动片P从R的最左端移到最右端的过程中电阻R增大 ,由闭合电路欧姆定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003728570706.png)
可知电流I减少,内电压减少,外电压增大,而电压表测得的是外电压,所以读数一定增大,A对,B错;R消耗的功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250037286011631.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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