题目内容
(10分)如图所示电路,电灯
,电动机绕组的电阻
,当电键S1、S2闭合时,测得电阻
的电功率是
,理想电流表的读数为
,求此时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241534409703977.jpg)
(1)电源的输出功率;
(2)电动机的输出功率。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153439816600.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153439862523.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153440050323.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153440159579.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153440330412.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241534409703977.jpg)
(1)电源的输出功率;
(2)电动机的输出功率。
(1)240W(2)135W
试题分析:(1)由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441032558.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441157585.png)
∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441282511.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441438554.png)
(2)流过电灯的电流I1= U1/R1=2A
流过电动机的电流I0=I—I1=3A
电动机的输入功率为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441594828.png)
电动机的热功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441656876.png)
∴电动机的输出功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153441859648.png)
得 P2="135" W
点评:此类题型属于非常经典的闭合电路欧姆定律结合非纯电阻元件的能量转化问题,非纯电阻不能直接用公式求解,而是需要通过能量守恒定律间接求解。
![](http://thumb2018.1010pic.com/images/loading.gif)
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