题目内容
如图所示电路,用伏安法测量电阻的大小。电阻R=320Ω时,电流表的示数是15 mA,电压表的示数是4.5 V。如果用这个电路测量未知电阻
,电流表的示数是13 mA,电压表的示数是5.2 V,则电阻
的大小是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241141187291264.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118682213.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118682213.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241141187291264.jpg)
A.![]() | B.400Ω<![]() |
C.![]() | D.无法确定 |
A
R=320Ω时,两端电压U="4.5" V,则通过R的电流
0. 014 A="14" mA
通过电压表的电流
1 mA
电压表内阻
4 500Ω
当电阻为
时,电压
=5.2V
通过电压表的电流
1.15 mA
通过
的电流
(13-1.15)mA="11.85" mA
电阻
439Ω。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118791345.gif)
通过电压表的电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118807316.gif)
电压表内阻
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118822472.gif)
当电阻为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118682213.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118853213.gif)
通过电压表的电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118869483.gif)
通过
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114118682213.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114119103341.gif)
电阻
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114119181488.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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