题目内容
如图所示电路中,电阻R1=3Ω,R2=3Ω,R3=6Ω,S扳至1时,电流表的示数为1.0A,S扳至2时,电流表示数为1.5A,求电源的电动势E和内阻r(电流表内阻不计,可分别画出两种情况下的等效电路图,分析电阻的串并联关系)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157136374285.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157136374285.jpg)
E=6V,r=1![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
S扳到1时,R1和R3并联再和R2串联
R13=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713653801.gif)
由闭合电路欧姆定律列式:E=I1(R13+R2+r)
S扳到2时, R1和R2串联再和R3并联
R12=3+3=6![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
R外=
=3![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
由闭合电路欧姆定律列式:E=I2(R外+r)
代入数值解得E=6V,r=1![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
R13=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713653801.gif)
由闭合电路欧姆定律列式:E=I1(R13+R2+r)
S扳到2时, R1和R2串联再和R3并联
R12=3+3=6
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
R外=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713684235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
由闭合电路欧姆定律列式:E=I2(R外+r)
代入数值解得E=6V,r=1
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713637215.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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