问题 实验题

如图甲是小明做“测量小灯泡电功率”的实验的电路图,已知电源电压为3V,小灯泡的额定电压为2.5V(阻值约为10W)

 

(1)小明在检查仪器时,发现电流表指针如图乙所示,则接下来的操作是                 

(2)小明在连接电路时,开关S应     ,电压表应选择         量程,闭合开关前滑片P应置于图中      (选填“最左端”或“最右端”)的位置。

(3)经检查无误后,闭合开关,调节滑动变阻器的滑片到某一位置,电流表和电压表的示数如图丙所示,则此时流过小灯泡的电流是        A,灯泡两端的电压是       V,灯泡的实际功率是       W。

(4)改变滑动变阻器的阻值,多次测量通过小灯泡的电流和它两端的电压,根据记录的数据,小明画出了小灯泡电流随其两端电压变化的关系图像(如图丁),根据图像提供的信息,计算出小灯泡的额定功率为       W,小灯泡灯丝电阻随电压增大而        (选填“增大”、“减小”或“不变”)。

答案

(1)校“零” (2)断开,0~3V,最左端

(3)0.22A,1.8V,0.396W (4)0.625W、增大

实验前,要看电表的指针是否指零刻度,不在零刻度要进行调零.连接电路时,开关处于断开状态和滑动变阻器处于最大阻值处都能保护电路.根据电源电压选择电压表的量程.根据小灯泡的额定电压为2.5V,阻值约为10Ω,确定电压表和电流表的量程,然后读出电压表和电流表的示数,根据P=UI计算灯泡的实际功率;根据小灯泡的额定电压为2.5V,结合U-I图象,找出对应的额定电流,根据P=UI计算灯泡的额定功率;观察U-I图象,由R=U/I计算出几组电阻,就可判断灯泡电阻的变化趋势.(1)实验前,电流表指针没有在零刻度,需要调零.

(2)连接电路时,开关处于断开状态,滑动变阻器处于最大阻值处,滑片要滑到最左端.

灯泡额定电压为0.25V,电压表使用0~3V量程.

(3)灯泡电流大约为0.25A,电流表使用0~0.6A量程,此时电流表示数为:I=0.22A,

灯泡额定电压为0.25V,电压表使用0~3V量程,电压表示数为:U=1.8V,

灯泡的实际功率:P=UI=1.8V×0.22A=0.396W.

(4)由U-I图象可知,当U=2.5V时,I=0.25A,所以P=UI=2.5V×0.25A=0.625W;

由U-I图象可知当U1=1.5V时,I1=0.2A,所以R1= U1/ I1=1.5V/0.2A=7.5Ω;

当U2=2.5V时,I2=0.25A,所以R2= U2/ I2=2.5V/0.25A=10Ω;

故小灯泡灯丝电阻随电压增大而增大;

点评:本题考查了用伏安法测灯泡电功率的实验中电压表、电流表、滑动变阻器的正确使用方法.对于电表量程的选择,应尽量使在不超过电表量程的前提下,使电表指针偏转幅度尽量大些,以保证可以多测几组数据,从而归纳出普遍结论。

阅读理解

阅读理解.

     The clock struck eleven at night. The whole house was quiet. Everyone was in bed

except me. Under the strong light, I looked sadly before me at a huge pile of that troublesome

stuff they call "books".

     I was going to have my examination the next day. "When can I go to bed?" I asked 

     The clock struck twelve. "Oh, dear!" I cried. "Ten more books to read before I can

go to bed!" We pupils are the most wretched creatures in the world. Dad does not agree

with me on this. He did not have to work so hard when he was a boy.

     The clock struck one. I was quite desperate now. I forgot all I had learned. I was too

tired to go on. I did the only thing I could. I prayed, "Oh God, please help me pass the

exam tomorrow. I do promise to work hard afterwards, Amen." My eyes were so heavy

that I could hardly open them. A few minutes later, with my head on the desk, I fell asleep.

1. The underlined word "wretched" in Paragraph 3 probably means _______.

A. happy

B. disappointed

C. unhappy

D. hopeful

2. Reviewing his lessons that night didn't help him because ______.

A. it was too late at nightB. he was very tired

C. his eyelids were so heavy that he couldn't keep them open

D. he hadn't studied hard before the examination

3. What do you suppose probably happened to the author the next day______.

A. He went to a church to pray again.

B. He passed the exam all by luck.

C. He failed in the exam.

D. He was punished by his teacher.

4. The best title for the passage would be ______.

A. The Night Before the Examination

B. Working Far into the Night

C. A Slow Student

D. Going Over My Lessons

问答题 简答题