题目内容
I.某同学在测一节干电池的电动势和内电阻的实验中,测得若干组电池两端电压值和对应的通过干电池的电流值,并利用这些数据画出了如图9所示的U-I图象.则由此U-I图象可知,该干电池的电动势的测量值为______V,内电阻的测量值为______Ω.(本题结果保留到小数点后2位)II.用电流表和电压表测一个电阻值约为25kΩ、额定功率为
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_ST/0.png)
①量程0~100μA,内阻约为500Ω的电流表A1
②量程0~500μA,内阻约为300Ω的电流表A2
③量程0~1V,内阻约为10kΩ的电压表V1
④量程0~15V,内阻约为100kΩ的电压表V2
⑤量程0~50V,内阻约为500kΩ的电压表V3
⑥直流稳压电源两端的输出电压为16V
⑦滑动变阻器,阻值范围 0~500Ω,允许最大电流 lA
⑧待测电阻Rx,开关和导线若干
(1)为了测量准确,电压表应选______,电流表应选______.(填写仪器前的序号)
(2)画出实验电路图.
(3)若测量值为R测,真实值为R真,那么在操作、读数、计算均正确无误的情况下,R测______R真(选填“大于”、“等于”或“小于”).
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_ST/images1.png)
【答案】分析:(1)电源的U-I图象与纵坐标轴的交点是电源电动势,图象斜率的绝对值等于电源内阻.
(2)电表量程的选择应根据待测电阻的额定电流和额定电压来选择,并且通过电表的电流应在满刻度的
~
之间较合理;当
<
时电流表应选内接法,
时电流表应选外接法;当要求电流从零调时或滑动变阻器最大阻值远小于待测电阻时变阻器应用分压式接法.
解答:解:(1)由图示图象可知,电源电动势是1.49V,![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/images5.png)
电源内阻r=
;
(2)解:①根据P=
可求出待测电阻的额定电压为
V,由于电源的输出电压只有16V,所以电压表应选④,由P=I2R可得额定电流
,所以电流表应选②
②因为
,所以电流表应用内接法接法,又滑动变阻器最大电阻远小于待测电阻阻值,所以应用分压式接法,电路图如图所示
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/images11.png)
③由电路图可知,电压表的读数是电流表内阻与待测电阻的和,根据欧姆定律可知,所以R测>R真.
故答案为:(1)1.49;0.90.
(2)④;②;电路如图;大于
点评:(1)要会由电源的U-I图象求电源电动势与电源内阻,要掌握图象法处理实验数据的方法.
(2)在电学实验中应通过计算选择器材和电路,要求通过电表的电流不小于量程的
,伏安法测电阻时根据比值当
与
时的大小选择电流表内外接法,当滑动变阻器最大电阻远小于待测电阻值时或题目要求电流从零调时,滑动变阻器应用分压式.
(2)电表量程的选择应根据待测电阻的额定电流和额定电压来选择,并且通过电表的电流应在满刻度的
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/0.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/1.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/2.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/3.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/4.png)
解答:解:(1)由图示图象可知,电源电动势是1.49V,
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/images5.png)
电源内阻r=
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/5.png)
(2)解:①根据P=
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/6.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/7.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/8.png)
②因为
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/9.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/images11.png)
③由电路图可知,电压表的读数是电流表内阻与待测电阻的和,根据欧姆定律可知,所以R测>R真.
故答案为:(1)1.49;0.90.
(2)④;②;电路如图;大于
点评:(1)要会由电源的U-I图象求电源电动势与电源内阻,要掌握图象法处理实验数据的方法.
(2)在电学实验中应通过计算选择器材和电路,要求通过电表的电流不小于量程的
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/10.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/11.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029200537373660660/SYS201310292005373736606008_DA/12.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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