问题 实验题

在测定电压为3.8V的小灯泡额定功率的实验中:

(1)某同学连实验电路如图所示,他的连接有三处明显的错误,请在图中把错误的地方指出来。

_________

_________

                    

(2)伏安法测量电功率的原理是              

(3)若用闭合开关之后,电压表的示数为3V,为了测灯泡的额定功率,则变阻器的滑片应向_________ 移动,直到电压表的示数等于 _________ 为止。

(4)若小灯泡正常发光时,如图所示,电流表示数为 _________ A,则小灯泡的额定功率是_________

(5)夏季的晚上七到十点是用电高峰期,此时加在灯泡两端的实际电压U<U,使得P ___      ____ P,灯也较暗;而夏季的下半夜是用电低峰期,此时加在灯泡两端的实际电压U>U,使得P________ P,灯则较亮;若实际电压远大于灯泡的额定电压,则灯丝可能会 _________

  

答案

(1)①电流表正负接线柱接反,

②电压表的量程选小,

③滑动变阻器没有调到最大;

(2)P=UI

(3)左;3.8V

(4)0.5;1.9W

(5)<;>;烧坏。

阅读理解

阅读理解。    

     Once there were two brothers who were twins. They looked exactly alike. They both had the same

dark brown hair, blue eyes and beautiful teeth. They were both 5'10" tall and both weighed 150 pounds.    

     They not only looked alike but also sounded alike on the telephone.  Not even their family could tell the difference. They dressed alike, listened to the same music, and read the same books. They even laughed at the same jokes.    

     When they were twenty-three ,they both got married and a year later both had sons. The years went by and as they began to grow old, they both wore glasses and finally they both became bald (秃头的). Then one day, one of the brothers got sick  and died. A few days later a man stopped the other twin on the

street.    

    “Excuse me for asking,” he said, “but was it you or your brother who died?” 

 l. It was not easy to tell the two men from each other because _________.   

A. they were brothers

B. they were handsome    

C. they were at the same age

D. they were twins  

2. The twin brothers ______.    

A. looked very much alike

B. had different colored hair    

C. looked like movie stars

D. wore different clothes  

3. They both became bald means ___.   

A. they became old

B. they had sons    

C. they had little hair

D. they got sick   

4.The only difference between the twins was ________.  

A. one was shorter than the other

B. one got sick and died    

C. one got married and had a son

D. one was bald and the other wasn't      

5. The man stopped the other twin on the street because______. 

A. he wanted to talk with him

B. he didn't know which of them died    

C. he wanted to make friends with him

D. he was surprised to see him on the street

选择题