题目内容
(10分)如图所示电路中,电阻R1=R2=R3=12Ω,当电键S断开时,电压表的示数为6V;电键S接在b点时,电压表的示数是7.8V。求:(电压表的内阻非常大,流过电压表的电流可忽略不计)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032196745172.jpg)
(1)电键S接a点时电压表的示数
(2)电源的电动势和内阻
(3)电键S接在b点时,电源总功率和电阻R3的功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032196745172.jpg)
(1)电键S接a点时电压表的示数
(2)电源的电动势和内阻
(3)电键S接在b点时,电源总功率和电阻R3的功率
(1)0 (2)
(3)
;![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032197521732.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003219721744.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032197361534.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032197521732.png)
试题分析:(1)电阻R1和电压表被短路,电压表示数为0
(2)S断开时
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032197832140.png)
S接b时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032197991103.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003219814798.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003219721744.png)
(3)S接b时
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032198451530.png)
电阻R3的功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250032198771726.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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