问题 实验题

(8分)在测定小灯泡电阻的实验中,已知该小灯泡的阻值约为5Ω左右,现备有以下器材:

A.电池组E(3V)

B.滑动变阻器R1(0~10Ω,额定电流2A)

C. 滑动变阻器R1(0~50Ω,额定电流1A)

D.电流表A1(0~3A,内阻约0.1Ω)

E.电流表A2(0~0.6A,内阻约0.5Ω)

F.电压表V1(0~3V,内阻约6kΩ)

G.电压表V2(0~15V,内阻约30kΩ)

G.电键、导线

(1)本实验中滑动变阻器、电流表、电压表应选用的是____________。(填写各器材前面的字母代号)

(2)请在方框中画出实验电路图,并以笔划线代替导线将实物图补充完整。

(3)在闭合开关S前,滑动变阻器触头应放在_________端。(选填“a”或“b”)

(4)该实验存在系统误差,误差的结果是测量值         真实值。(选填“大于”或“小于”)

答案

(1)①BEF(2分)  ②  电路图见解析(4分 )   ③b (1分)   ④小于(1分)

题目分析:(1)由于电源电压为3V,因此电压表选F测量准确;由于待测电阻5,因此回路中的电流最大值为,因此电流表选E,滑动变阻器阻值接近待测电阻时,调节起来比较方便,因此滑动变阻器选B。

(2)由于待测电阻值小较小,因此选用电流表外接法,滑动变阻器采用限流法就可以较准确测量出灯的电阻,连接电路如图所示。(当然滑动变阻器采用分压式也可以)如图所示

(3)采用分压式时,闭合电键前,滑动变阻器调到最大值,使得回路电流最小,以保护电压表和电流表。因此滑动变阻器的触头调到b端

(4)由于采用电流表的外接,因此测量值小于真实值,

单项选择题
阅读理解

E

A year after graduation, I was offered a position teaching a writing class. Teaching was a profession I had never seriously considered, though several of my stories had been published. I accepted the job without hesitation, as it would allow me to wear a tie and go by the name of Mr. Davis. My father went by the same name, and I liked to imagine people getting the two of us confused. “Wait a minute” someone might say, “are you talking about Mr. Davis the retired man, or Mr. Davis the respectable scholar?”

The position was offered at the last minute, and I was given two weeks to prepare, a period I spent searching for briefcase (公文包) and standing before my full-length mirror, repeating the words, “Hello, class. I’m Mr. Davis.” Sometimes I would give myself an aggressive voice. Sometimes I would sound experienced. But when the day eventually came, my nerves kicked in and the true Mr. Davis was there. I sounded not like a thoughtful professor, but rather a 12-year-old boy.

I arrived in the classroom with paper cards designed in the shape of maple leaves. I had cut them myself out of orange construction paper. I saw nine students along a long table. I handed out the cards, and the students wrote down their names and fastened them to their breast pockets as I required.

“All right then,” I said. “Okey, here we go.” Then I opened my briefcase and realized that I had never thought beyond this moment. I had been thinking that the students would be the first to talk, offering their thoughts and opinions on the events of the day. I had imagined that I would sit at the edge of the desk, overlooking a forest of hands. Every student would yell. “Calm down, you’ll all get your turn. Once at a time, once at a time!”

A terrible silence ruled the room, and seeing no other opinions, I inspected the students to pull out their notebooks and write a brief essay related to the theme of deep disappointment.

小题1:The author took the job to teach writing because ______.

A.he had written some stories

B.he wanted to be expected

C.he wanted to please his father

D.he had dreamed of being a teacher小题2:Before he started his class, the author asked the students to ______.

A.write down their suggestions on the paper cards

B.cut maple leaves out of the construction paper

C.cut some cards out of the construction paper

D.write down their names on the paper cards小题3:What did the students do when the author started his class?

A.They began to talk.

B.They stayed silent.

C.They raised their hands.

D.They shouted to be heard.小题4:The author chose the composition topic probably because ______.

A.he got disappointed with his first class

B.he had prepared the topic before class

C.he wanted to calm down the students

D.he thought it was an easy topic