题目内容
某一阻值不变的纯电阻元件(阻值Rx约100Ω),额定功率为0.25w,要用伏安法较准确地测量它的阻值,实验器材有:
电流表A1:量程为60mA,内阻约为5Ω;
电流表A2:量程为1A,内阻约为0.5Ω;
电压表V1:量程为6V内阻约为10kΩ;
电压表V2:量程为30V,内阻约为50kΩ;
滑动变阻器R:0~10Ω,2A;
电源(E=9V),开关,导线若干。
(1)实验中应选用电流表为 ,电压表为 ;(填入器材符号)
(2)在虚线框内画出实验电路图:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241527103162769.jpg)
(3)实验中电阻测量值与真实值相比 (填“偏大”、“偏小”或“相等”)
电流表A1:量程为60mA,内阻约为5Ω;
电流表A2:量程为1A,内阻约为0.5Ω;
电压表V1:量程为6V内阻约为10kΩ;
电压表V2:量程为30V,内阻约为50kΩ;
滑动变阻器R:0~10Ω,2A;
电源(E=9V),开关,导线若干。
(1)实验中应选用电流表为 ,电压表为 ;(填入器材符号)
(2)在虚线框内画出实验电路图:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241527103162769.jpg)
(3)实验中电阻测量值与真实值相比 (填“偏大”、“偏小”或“相等”)
(1)
;
(2)实验电路图如图所示
(3)偏小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152710784342.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152710847356.png)
(2)实验电路图如图所示
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241527109725401.jpg)
(3)偏小
试题分析:(1)电源电动势为9V,电路中的最大电流为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241527109871085.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152711050367.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152710784342.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152711174386.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152710847356.png)
(2)由于
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241527117201012.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152710847356.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241527119703588.jpg)
(3)电流表外接,由于电压表的分流作用,所以测量值比真实值偏小。
点评:本题关键,一要根据要求选择合适器材;二要选择合适的电路。
![](http://thumb2018.1010pic.com/images/loading.gif)
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