题目内容
(8分)如图所示电路,R3=12Ω,当滑动变阻器R1调到6Ω时,电源的总功率为P=63W,输出功率为P出=54W,电源的内电阻为r=1Ω。求电源电动势E和流过滑动变阻器R1的电流I1。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032551012459.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032551012459.jpg)
21V,2A.
试题分析:
根据功能关系和闭合电路欧姆定律有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003255117441.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003255148530.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003255164569.png)
由于R1和R3并联,根据并联电路关系有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003255179461.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003255195538.png)
联解①②③④⑤式并代入数据得:
E=21V ⑥
I1=2A ⑦
评分参考意见:本题满分8分,其中③式2分,①②④⑤⑥⑦式各1分;若有其他合理解法且答案正确,可同样给分。
![](http://thumb2018.1010pic.com/images/loading.gif)
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