题目内容
(10分)如图所示电路中,两个电流表A1和A2的示数分别为0.20A和0.30A,当R1和R2交换位置后,两电流表示数不变。各电流表的内阻不计,则电流表A3的示数是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412481160214163.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412481160214163.png)
0.35A
有电路图可知,三个电阻并联,并且
测量的是通过
、
的总电流;
测量的是通过
的总电流;而
测量的是通过三个电阻的总电阻;当调换
的位置后个电流表示数不变,说明
,即
,由此可得:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124812007670.png)
所以通过
的电流为0.35A
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811633330.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811664312.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811695321.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811726331.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811742378.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811882339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811742378.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811929380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811945336.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124812007670.png)
所以通过
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124811882339.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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