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用如图所示的电路测定一节铅蓄电池的电动势和内阻．因蓄电池的内阻较小，为防止调节滑动变阻器时造成短路，电路中用了一个保护电阻R0．除蓄电池、开关、导线外，可供使用的实验器材还有：

A．电流表A1：量程为0.6A；

B．电流表A2：量程为3A；

C．电压表V1：量程为3V；

D．电压表V2：量程为15V；

E．定值电阻R01（阻值2.0Ω、额定功率5W）

F．定值电阻R02（阻值10Ω、额定功率10W）

G．滑动变阻器R1（阻值范围0～10Ω、额定电流2A）

H．滑动变阻器R2（阻值范围0～200Ω、额定电流1A）

（1）电流表应选用______，定值电阻应选用______，滑动变阻器应选用______．（填写器材前的字母代号）

（2）实验中调节滑动变阻器共测得五组电流、电压的数据，如下表．

电流表示数I/A0.160.340.420.520.58
电压表示数U/V1.901.791.751.691.66
请作出蓄电池路端电压U随电流I变化的U-I图象，

并根据图象得出蓄电池的电动势为______V，内阻为______Ω．

只考虑由于电表不是理想表而引起的系统误差，则测出的电动势与真实值相比______，测出的内阻与真实值相比______．（填“偏大”、“等于”或“偏小”）．

答案

（1）一节铅蓄电池的电动势约为2V，为了多次几组实验数据，电路电流变化量应大一些，因此保护电阻阻值不能太大，保护电阻应选定值电阻：E．定值电阻R01（阻值2.0Ω、额定功率5W）；电动势约为2V，保护电阻阻值为2.0Ω，则电路最大电流不超过1A，为减小电流表的读数误差，电流表应选A．电流表A1：量程为0.6A；为方便实验操作，滑动变阻器应选最大阻值较小的滑动变阻器，因此滑动变阻器应选：G．滑动变阻器R1（阻值范围0～10Ω、额定电流2A）．

（2）根据表中实验数据在坐标系中描出对应的点，然后根据描出的点作出U-I图象如图所示；由U-I图象可知，蓄电池的电动势

E=1.98V，内阻r=

△U
△I
=
1.98-1.60
0.68
≈0.56Ω；由于电压表的分流，导致电流测量值小于真实值，只有电路的短路电流等于真实值，测量值与真实值的U-I图象如（下）图所示，由图象可知，蓄电池电动势与内阻的测量值均小于真实值．

故答案为：（

1）A；E；G；（2）图象如图所示；1.98；0.56；偏小；偏小．

单项选择题

足少阳胆经作为阳经循行于（）。

A.身侧边

B.身前

C.身后

D.足阳明胃经内侧

E.足太阳膀胱经内侧
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阅读理解

      "Everything happens for the best," my mother said whenever I was disappointed. "Don't worry. One

day your luck will change."

      I didn't pay attention to her words. After finishing my college education, I decided to look for a job

in a radio station. I wanted to host a sports programme. I went to Chicago and knocked on the door of

every station. But I got turned down every time.

     In one station, a kind lady said to me that I hadn’t got enough experience. "Get to a small station and

work for some time," she said.

     When I went back home, my dad told me that a businessman had opened a store and needed someone to help him. But again, I didn't get the job.

     I felt really down. "Your luck will change," Mum said to me. Later, I tried another radio station in Iowa. But the owner, a nice man, told me he had already had someone to work for him. As I left his office, I

asked, "How can someone be a sports announcer (播音员) if he can't get a job in a radio station?"

     I was waiting for the lift when I heard the man call, "What did you mean? Do you know anything about football?" He let me sit in front of a microphone and asked me to try to imagine that I was giving my

opinion on a football game, and finally I succeeded.

     On my way home, Mum's words came back to me, "One day your luck will change, Son."

1. What was the writer's ideal（理想的）job?

A. A sportsman.                          

B. A shop assistant.        

C. A sports announcer.                      

D. A businessman.

2. Why didn't the writer get the job in Chicago?  

A. Because he was too young.

B. Because he didn't get a college education.

C. Because he was not a good-looking person.    

D. Because he hadn't got enough experience.

3. The sentence "I got turned down every time" means "           ".

A. I was refused every time            

B. I was successful every time

C. I lost my way every time            

D. The door of every station was closed

4. The writer got a job             in the end.    

A. in Chicago                          

B. in his home town

C. in a college                            

D. in Iowa
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