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,

选择题
阅读理解

阅读理解。

                                                              History has arrived

      Nine-year-old Barack Obama was looking through magazine. But the African-America boy was shocked by

a series of photos. The pictures were of a black man who destroyed his skin with chemicals that promised to

make him white.

     For the first time, the boy began to doubt who he was. "I stood in front of the mirror and wondered if

something was wrong with me," Obama said.

     However, now the boy who used to struggle with his identity doesn't see it as a problem any more, but an

advantage for his career. Last week, Obama made history by being elected as the first black president of the

US. He defeated John MaCain in a landslide (压倒性的) victory.

     Obama's story starts in opposite corners of the world. His white mother was born in the heartland of the

US. His black father grew up in a tiny village in Kenya. They met during in Hawaii, but his father left the family when Obama was just two years old and his mother moved to Indonesia.

     At 10, Obama moved back to live with his white grandparents in Hawaii where his sense that he didn't

belong grew. At his class a white boy asked Obama if his father ate people. Out of embarrassment, Obama lied

to his classmates that his father was prince, "I kept asking who I am and I ended up trying drugs and

drinking," Obama recalled.

     Things came to change after the young man made friends with those with a similar background at college.

Their experiences back in Africa helped Obama to finally face up to his African origin. He worked hard to

become a star at Harvard Law School and the third black senator (参议院) in US history.

     At the beginning of his campaign for the White House, few people viewed Obama favorably (赞同地).

Many doubted his unusual background, which left him neither "black" enough nor white enough.

     But Obama turned his pain of growing up into a tool to make Americans believe: "There is not a black

America, an Asian America. There's the United States of America."

     Barack Obama's victory is "a historic victory that promised change and overcame centuries of prejudice

(偏见). His success fulfilled Martin Luther King's dream that a man he judged not by the color of his skin, but

by the content of his character," wrote ABC news.

1. From the above passage we can know that Barack Obama was born in ______.

A. Kenya, Africa

B. Hawaii, the USA

C. Indonesia, Asia

D. an unknown city, in Latino America

2. He lied to his classmates that his father was prince because ______.

A. he felt ashamed of his African origin

B. he had unusual background- neither black nor white

C. his black father deserted him when he was very young

D. he didn't have the sense of belonging

3. Put the following things in order of time.

a. Obama is the third black senator(参议院) in US history

b. Obama's mother settled down in Indonesia with Barack Obama

c. Obama stood out among his classmates in Harvard Law School

d. Obama lived with his white grandparents in Hawaii

e. Obama's black father left him and his mother

A. c, d, a, b, e

B. e, d, b, c, a

C. d, b, a,e, c

D. e, b, d, c, a

4. What does the title "History has arrived" probably mean?

A. Barack Obama eventually defeated his white opponent, John MaCain in a landslide victory.

B. Barack Obama's victory has given blacks and other minorities a true national role model.

C. Barack Obama has become the first African-American President, overcoming centuries of prejudice.

D. Through his great efforts, Barack Obama became the third black senator in the US history.