题目内容
(16分)如图所示,AB、CD为两根平行的相同的均匀电阻丝,EF为另一根电阻丝,其电阻为R,它可以在AB、CD上滑动并保持与AB垂直,EF与AB、CD接触良好.图中电压表为理想电压表.电池的电动势和内阻都不变.B、D与电池两极连接的导线的电阻可忽略.当EF处于图中位置时,电压表的读数为U1="4.0" V.已知将EF由图中位置向左移动一段距离△L后,电压表的读数变为U2="3.0" V.若将EF由图中位置向右移动一段距离△L,电压表的读数U3是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008336912371.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008336912371.jpg)
6 V
试题分析:假设电源的电动势为E,内阻为r,E、B之间的长度为x,两电阻丝单位长度上的电阻为△R,根据题意和闭合电路的欧姆定律有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000833706897.png)
电压表的示数为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000833738493.png)
当向左移动时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008337531134.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000833769520.png)
当向右移动时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008337841119.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000833816530.png)
联系以上各式,根据已知数据可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000833831571.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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