问题 问答题

伏安法测电阻,当被测电阻不知估计值时,在连接测量电路时可采用以下试接的方法:电压表一端连接于电路中C点,另一端分别接电路中a点或b点(图中用单刀双掷开关K进行变换),观察两电表读数变化情况,来选择电流表的接法.设两表的量程及所接电源都合适.

(1)当K分别接a和接b时,发现电流表读数比电压表计数变化明显,则应采用K接______点的方法

(2)用上述接法测出的Rx值比它的真实值______.误差是由于______造成的.

(3)若已知电压表内阻RV,电流表内阻RA,测量时电压表和电流表读数分别为U和I,则被测电阻真实值计算表达式Rx=______

(4)要描绘出该被测电阻的伏安特性曲线,除上面图示中测量电路中已有的器件外,还有电源、开关、导线和______.并把测量电路的E、F两点接入完整的电路中(画出虚线内的电路图)

答案

(1)当K分别接a和接b时,发现电流表读数比电压表计数变化明显,说明电流表的分压作用较小,所以要用内接法,即应采用K接a点的方法;

(2)用此接法电压表测量的是电流表和被测电阻的总电压,电流表测量的是被测电阻的电流,根据欧姆定律R=

U
I
可知,电压偏大,电流准确,所以电阻值偏大;

(3)电阻两端的电压U′=U-IRA

根据欧姆定律R=

U′
I
得:

Rx=

U-IRA
I

(4)要描绘出该被测电阻的伏安特性曲线,则要得出多做U、I值,所以要用到滑动变阻器调节电路,为了使被测电压可以从零开始,所以滑动变阻器要用分压式,

电路图如图所示:

故答案为:(1)a点

(2)偏大;电流表的分压

(3)

U-IRA
I
   

(4)滑动变阻器,如图所示.

阅读理解

信息匹配(共5小题;每小题2分,满分10分)

阅读下列应用文及相关信息,并按照要求匹配信息。请在答题卡上将对应题号的相应选项字母涂黑。请阅读以下学生的基本信息,为他们选择合适的团体。

小题1:.Nancy comes from China and wants to join a club that can help her know more about   America.Her major is linguistics which requires her to know the cultural differences.And she is busy on weekends because of her part—time job.

小题2:Catty is an outgoing person.She loves nature very much and always goes cycling around the university.Since she is not familiar with America,she wants to know more about it.

小题3:Both of Margaret’s parents are doctors.She has been wanting to be a doctor since she was a little girl.She hopes that the club will help her get to know more about the recent development on medicine.

小题4:Thompson always gave a performance in his middle school whenever there was an event.He loves music and movies very much.But he is busy finishing his course and has no time to attend the club meetings.

小题5:Lucy always keeps an eye on the daily life problems that happen around the campus.She is ready to help others and she hopes that she can help more people through the club.

The information about extra curricular activities

A.Asian—American Students Union

Set up for more than thirty years,this club has been mainly focusing on the cultural differences between Asia and America.The members in this club should come from Asia or America and they will hold a meeting every Thursday evening to discuss the interesting points they have found in their daily lives.Besides,they will conduct some surveys among their classmates to dig the roots of the differences.

B.Yale Film Society

Students who are movie-lovers come here to enjoy wonderful movies together and they will learn the actors’ lines.More than that,some nice films produced by themselves will have the chance to be praised by teachers and students on the campus.They will get together every Friday night to hold a small meeting where they will have their opinions exchanged and may recommend some new movies.

C.Yale AIDS Watch

All the members in this club should have some basic knowledge about AIDS and be interested in the serious headache for the people all around the world---AIDS. They will collect the latest reports on the development of the study of the disease.At the same time,they will have some leaflets printed to give out to the students.The time for them to meet is Friday afternoon twice a month.

D.Society of WomenThe members are female only and they will pay attention to the problems they come across in their school lives and outside the campus.All the girls are welcome to this club as long as they want to protect their rights as women.They will get together every Sunday afternoon to deal with the letters from girls and try to solve their problems.

E.Yale Pop Band

This band has been very popular among students who are keen on pop music.The members introduce latest albums and most of them are good at singing and each of them plays a key role in any party.They have no regular meetings but keep in touch by mail.

F.Yale Camping Club

There are many opportunities for the members to go hiking or sightseeing.If the weather allows,they will camp along the seaside or river banks.It attracts many students who come from abroad because this will give them opportunity to see more places in the US.

单项选择题