问题 实验题

在《练习使用多用电表》的实验中:

(1)用欧姆档测量一定值电阻的阻值。机械调零、欧姆调零后,用“”档测量,发现表针偏转角度极小,正确的判断和做法是            

A.被测电阻值很大

B.被测电阻值很小

C.为了把电阻值测得更准一些,应换用“” 档,重新欧姆调零后再测量

D.为了把电阻值测得更准一些,应换用“” 档,重新欧姆调零后再测量(2)某同学用多用电表欧姆档测量一只“220V,100W”的白炽灯的灯丝电阻,测出其阻值是64Ω,他又用公式R =U2/ P =2202/100算出了灯丝的电阻却是484Ω,两者明显不等。他所使用的电表以及整个测量的过程均没有任何问题。造成电阻不等的原因是       

答案

(1)A、C  ;(2)用公式算出的是灯正常工作时的电阻。温度升高,电阻率变大,因此电阻变大

题目分析:(1)发现表针偏转角度极小,说明电阻很小,需要应换用“” 档,重新欧姆调零后再测量,AC正确,

(2)用公式算出的是灯正常工作时的电阻。温度升高,电阻率变大,因此电阻变大

点评:在使用欧姆表时,指针偏小,说明被测电阻很小,需要换用较小的档位,指针偏转角度大,被测电阻较大,需要换用较大的档位

阅读理解

阅读理解。

     Mr Jones has a special way of waking Lily in the morning. He sends Lily's dog, Frank, into her bedroom.

Frank jumps up and licks (舔) Lily's face, then Lily gets out of her bed. That's how every school day starts.

     One Monday morning, Lily got out of bed and looked at the clock. It was 6:45. Lily washed and dressed.

She moved quickly. She knew she didn't have much time to get ready for school. The school bus usually stops

at the corner of her street at 7:30. She has to be at the bus stop by then.

      "What's for breakfast?" asked Lily. Her father gave her two eggs and a glass of orange juice.

      "Hurry up," said Mr Jones."Where's your homework? Do you have that note I gave you for Mrs Brown?

Don't forget it. Here's your lunch money."

     Lily got her books and homework all together. She found the note and took the lunch money. She put

everything in her schoolbag. Then she rushed off to catch the bus at 7:30.

     The bus was right on time. Lily got on and sat down next to her friend Bill. Then Lily and Bill started to

tell each other jokes. It was nice to relax.

1. In the morning  _______ wakes up Lily.

A. Mrs Jones

B. Mr Jones

C. Frank

D. the clock

2. One Monday morning Lily got up at ________.

A. 6: 45

B. 7: 00

C. 7: 20

D. 7: 30

3. Lily had to take ________ to Mrs Brown.

A. her homework

B. her dog

C. lunch money

D. a note

4. This passage tells us Lily usually ________ to school.

A. walks

B. rides her bicyle

C. takes the bus

D. takes the subway

5. Which of the following is TRUE?

A. Lily has a dog.

B. Mrs Jones is an English teacher.

C. Bill is Lily's brother.

D. Lily likes hamburgers for breakfast.

填空题