题目内容
(8分)如图所示电路中,电阻R1=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:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241606277777803.png)
(1)电源的电动势E和内阻r(电流表内阻不计);
(2)S扳至2时,电源的输出功率。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241606277777803.png)
(1)电源的电动势E和内阻r(电流表内阻不计);
(2)S扳至2时,电源的输出功率。
(1)E=6.0V,r=1.0Ω(2)6.75W
试题分析:如图,开关S扳至1时,电阻R1、R3并联后与R2串联.S扳至2时,电阻R1、R2串联联后与R2并联.分别求出外电路总电阻,根据闭合电路欧姆定律列出两个方程,组成方程组求解电源的电动势E和内阻r。
(1)根据闭合电路欧姆定律得
当开关S接1时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160628011970.png)
当开关S接2时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241606281201043.png)
代入数据,求解方程组
得:E=6.0V,r=1.0Ω
(2) S扳至2时
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160628385468.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160628619168.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241606288061035.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160628994876.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160629118976.png)
点评:关于电源的电动势和内电阻的求解,经常出现两种情况,根据闭合电路欧姆定律列两个方程,组成方程组求解.
![](http://thumb2018.1010pic.com/images/loading.gif)
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