题目内容
如图所示,电阻R1 = 2Ω,小灯泡L上标有“3V,1.5W”(灯泡的电阻不随温度变化),电源内阻r = 1Ω,滑动变阻器的最大阻值为R0(大小未知).当触头P滑动到最上端 a时, 安培表的读数为l A(其电阻不计),小灯泡L恰好正常发光,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241525485883867.jpg)
(1)滑动变阻器的最大阻值R0;
(2)电源的电动势E多大;
(3)当触头P滑动到最下端 b时电源的效率多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241525485883867.jpg)
(1)滑动变阻器的最大阻值R0;
(2)电源的电动势E多大;
(3)当触头P滑动到最下端 b时电源的效率多大?
(1)6Ω (2)6V (3)89%
试题分析:(1)触头P滑到a端,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152548635336.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152548775803.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152548853690.png)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152548993650.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152549305829.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152549633883.png)
(3)P滑到b,灯被短路,
则电源的效率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241525497891698.png)
点评:本题是简单的电路的分析和计算问题,这类问题首先要搞清电路的结构,其次要把握电流、电压的分配关系。
![](http://thumb2018.1010pic.com/images/loading.gif)
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