题目内容
(12分) 如右图所示,一个变阻箱与理想电流表串联后接到电源上,用一个理想电压表直接
连接在电源两端,开关K闭合后调整变阻箱的阻值,发现电路中的电流为0.4A时,电压
表的示数为2.8V,当电阻变小电流变为0.6A时,电压表示数为2.7V。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521785359.png)
(1)电源的电动势和内电阻。
(2)变阻器阻值调为2.5Ω,电流表、电压表的示数。
(3)变阻器阻值调为2.5Ω,电源的输出功率和效率各为多少?
连接在电源两端,开关K闭合后调整变阻箱的阻值,发现电路中的电流为0.4A时,电压
表的示数为2.8V,当电阻变小电流变为0.6A时,电压表示数为2.7V。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521785359.png)
(1)电源的电动势和内电阻。
(2)变阻器阻值调为2.5Ω,电流表、电压表的示数。
(3)变阻器阻值调为2.5Ω,电源的输出功率和效率各为多少?
:(1)
(2)1A 2.5V (3)83.3%
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521832498.png)
:
试题分析:(1)根据闭合电路欧姆定律![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521910569.png)
当
时
,则![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522128683.png)
当
时
,则![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522550674.png)
联解得
, ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522706530.png)
(2)当变阻器阻值为
时
根据闭合电路欧姆定律![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241445232201079.png)
由部分电路欧姆定律![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523314434.png)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523423919.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523470875.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241445235641133.png)
点评:闭合电路欧姆定律的应用,充分利用题目的已知条件,结合欧姆定律I=
列方程求解,有时求电流I是关键,I是联系内外电路的桥梁
试题分析:(1)根据闭合电路欧姆定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521910569.png)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521957526.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522035612.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522128683.png)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522175537.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522300589.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522550674.png)
联解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144521832498.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522706530.png)
(2)当变阻器阻值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144522815398.png)
根据闭合电路欧姆定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241445232201079.png)
由部分电路欧姆定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523314434.png)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523423919.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523470875.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241445235641133.png)
点评:闭合电路欧姆定律的应用,充分利用题目的已知条件,结合欧姆定律I=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144523642482.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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