题目内容
(6分)现要测量某一电压表V的内阻。给定的器材有:待测电压V(量程2V,内阻约4k
);电流表mA(量程1.2mA,内阻约500
);直流电源E(电动势约2.4V,
阻不计);固定电阻3个;R1="4" 000
,R2="10" 000
,R3="15" 000
;电键S及导线若干。
要求:测量时两电表指针偏转均超过其量程的一半。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152348046583.png)
i.试从3个固定电阻中选用1个,与其它器材一起组成测量电路,并在虚线框内画出测量电路的原理图。(要求电路中各器材用题中给定的符号标出。)
ii.电路接通后,若电压表读数为U,电流表读数为I,则电压表内阻RV= 。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152347688333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152347688333.png)
阻不计);固定电阻3个;R1="4" 000
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152347688333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152347688333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152347688333.png)
要求:测量时两电表指针偏转均超过其量程的一半。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152348046583.png)
i.试从3个固定电阻中选用1个,与其它器材一起组成测量电路,并在虚线框内画出测量电路的原理图。(要求电路中各器材用题中给定的符号标出。)
ii.电路接通后,若电压表读数为U,电流表读数为I,则电压表内阻RV= 。
i.电路图请画在方框中
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241523482497271.png)
ii.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241523482497271.png)
ii.
试题分析:电源的电动势为2.4v,而电压表的量程为2v,故要测量电压表的内阻,需知道电压表两端的电压(可直接从电压表上读出)和流经电压表的电流,由于要求电流表和电压表的示数要大于其量程的一半,故需要为待测电压表并联定值电阻,而流经电压表的电流可用毫安表的示数减去流经定值电阻的电流,电压表的示数除以定值电阻的阻值就是流经定值电阻的电流.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241523483584665.jpg)
i.根据闭合电路欧姆定律可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152348436690.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241523486241408.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152348702690.png)
故固定电阻应选
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152348858304.png)
ii.流过定值电阻的电流大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152349029401.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152349092450.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824152349185943.png)
点评:掌握了实验的基本原理就能驾轻就熟的解决各种问题,所以在日常的学习过程中要加强对基本原理的学习和积累.
![](http://thumb2018.1010pic.com/images/loading.gif)
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