题目内容
某同学要测定一电源的电动势
和内电阻
,实验器材有:一只DIS电流传感器(可视为理想电流表,测得的电流用
表示),一只电阻箱(阻值用
表示),一只开关和导线若干。该同学设计了如图甲所示的电路进行实验和采集数据。
(1)该同学设计实验的原理表达式是
(用
、
、
表示);
(2)该同学在闭合开关之前,应先将电阻箱调到 (填“最大值”、“最小值”或“任意值”),实验过程中,将电阻箱调至如图乙所示位置,则此时电阻箱接入电路的阻值为 Ω;
(3)该同学根据实验采集到的数据作出如图丙所示的
—R图像,则由图像可求得,该电源的电动势![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195414805322.png)
V,内阻r= Ω(结果均保留两位有效数字)。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082419541975016968.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195411997312.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195412761234.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195413338246.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195414181317.png)
(1)该同学设计实验的原理表达式是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195414805322.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195412761234.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195413338246.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195414181317.png)
(2)该同学在闭合开关之前,应先将电阻箱调到 (填“最大值”、“最小值”或“任意值”),实验过程中,将电阻箱调至如图乙所示位置,则此时电阻箱接入电路的阻值为 Ω;
(3)该同学根据实验采集到的数据作出如图丙所示的
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195418190300.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195414805322.png)
V,内阻r= Ω(结果均保留两位有效数字)。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082419541975016968.jpg)
(1)E= I(R+r)(2)最大值 21
(3)E=6.3V, r= 2.5![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195420187310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195420187310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195420187310.png)
试题分析:(1)由图可知,本实验采用的是电流表与电阻箱测定电动势,故表达式应为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195421856594.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195422823616.png)
(2)为了保证电路中的安全,电阻箱应从最大值开始慢慢减小,故开始时应调到最大值;
由图可知,电阻箱接入电阻应为21Ω;
(3)由闭合电路欧姆定律可知:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195423634645.png)
由数学知识可知,图象与纵坐标的交点为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195424492594.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195425428357.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195426021426.png)
故E=6.3V;r=2.5Ω;
点评:本题采用安阻法测电源的电动势,本方法的关键在于能列出电流与滑动变阻器的关系,再结合图象求出电动势和内电阻.
![](http://thumb2018.1010pic.com/images/loading.gif)
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