题目内容
.如图所示,均匀的长方形薄片合金电阻板abcd,ab边长为L1,ad边长为L2。当端点Ⅰ、Ⅱ或Ⅲ、Ⅳ接入电路时,导体的电阻分别为R1、R2,则R1:R2为 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241504305242371.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241504305242371.jpg)
A.L1:L2 | B.L2:L1 |
C.![]() ![]() | D.![]() ![]() |
C
试题分析:设导体的厚度为d,
当把端点Ⅲ、Ⅳ接入电路时,而
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150431226413.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150431398559.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150431460341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150431570939.png)
当把端点Ⅰ、Ⅱ接入电路时,而ad边为L2,
则此时导体的横截面积为:S2=L2d,
而此时导体的长度为L1,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824150431679940.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241504318041272.png)
点评:本题的关键是对导体长度的正确判断,
![](http://thumb2018.1010pic.com/images/loading.gif)
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