问题 实验题

物理课上,王老师请同学们设计一个测出未知电阻RX的电路,各组同学都提出自己的设计方案,下面是其中两组同学的实验方案:

甲组:张晴小组设计方案

器材:电压表、电流表、滑动变阻器(最大阻值已知)、开关、电源(电压未知)、未知电阻Rx、导线

电路图:如图1所示;

操作过程:闭合S电压表读数是U,电流表读数是I

乙组:赵亮小组设计方案

器材:已知电阻R0、电流表、开关、电源(电压未知)、未知电阻Rx、导线

电路图:如图2所示;

操作过程:电流表读数S断开时为I1;S闭合时为I2

(1).请你根据他们各自的电路图及操作过程写出未知电阻Rx的表达式:

甲组:Rx=_________;

乙组:Rx= _________

(2).甲组同学的原理图如果去掉电压表还能有办法测出未知电阻Rx吗?

答: _________ (选填“能”或者“不能”)

(3).甲组同学正确接线后实验时,发现无论怎样移动变阻器的滑片,V表的示数很大且不变,而A表指针几乎不偏转,则电路故障可能是 _________

                                                           图1                                      图2

答案

(1)

(2)不能;

(3)未知电阻RX断路.

阅读理解

Last week, while visiting my dad with my daughter, we went to a restaurant for dinner. When we were seated, my dad asked the waitress if there were any soldiers eating at the restaurant. Then waitress said there was a soldier having dinner with his friend. My dad told the waitress to tell the soldier and his friend that their dinner was paid for! He also said that he did not want to be known as the benefactor(施主).

Then waitress later commented on my dad’s thoughtful behavior saying that she had never seen anything like this before. At a local college, she had studied opera and so she used this to thank my dad by performing a piece from The Pearl Fisherman. Her voice brought me to tears because it sounded perfect!

After a while, the soldier appeared at our table (I don’t know how he knew my dad paid the bill for him.) and said that he would be sent to the front the next morning and that he could not leave this country without saying “thanks” to my dad. My dad replied that it was he who wanted to say “thanks”. They shook hands as the soldier left.

Before we left, the waitress came by again. She did a magic show as another way to show her

“thanks” to my dad. Her show was really great. My dad left her a note with email address asking for her next performance time in addition to a $ 50 tip.

Everyone witnessed something exemplary(可作榜样的) in the human spirit that night. I can only hope to see more of this in the future.

68.What did the soldier do in response to the author’s father’s kindness?

A.He gave something to author’s dad.

B.He gave a big tip to the waitress.

C.He said thanks to the author’s dad in person.

D.He did a magic show for the author and her father.

69.The author considered her father’s action to be ____.

A.funny       B.understandable C.worthless  D.honorable

70.Their passage mainly tells us that we should ____.

A.learn to be grateful to others B.find ways to thank others

C.try to learn from each other    D.respect soldiers and waitresses

单项选择题