问题 计算题

如图所示,电源电压为12V保持不变。当开关S闭合时,电流变的示数为0.25A,电压表的示数为4V。求:

(1)电阻R的阻值。

(2)若将R换为阻值为8Ω的电阻R1,求此时电压表的示数。(小灯泡L的阻值不变)

答案

(1)32Ω (2)8V

题目分析:此电路为灯L与电阻R串联,电压表测的灯L两端电压。

电阻R两端电压为UR=U-UL=12V-4V=8V

电阻R的阻值:

灯L的电阻为:

把电阻R换为R1后,电源电压不变,灯的电阻不变

此时电路总电阻为:R=RL+R1=16Ω+8Ω=24Ω

电路中的电流为:

此时电压表的示数为:UL’=IRL=0.5A×16Ω=8V

阅读理解

阅读理解。

     When I started teaching at school, I was sure I would change the world and touch children who needed love.  

     Although my students seemed to respond pretty well to my teaching, there was a small group of girls

who became more and more hostile (敌对的) towards me.

     One day a fight happened in my classroom. Attempting to end it, I stepped in (居中调停) to face one of these hostile young women, who started hitting me in the face. Two boys jumped up to control the girl,

but the damage was done.

     While the girl was suspended (暂时停学) for a few days, I was determined that she would not return

to my classroom. But I also prayed. I wanted to see all the students right there in my daily work at school.

     On the top of my daily lesson-plan book, I wrote this statement, "To see all the children in my

classroom is always beautiful." With this view I could expect to heal any anger towards the girl in my heart.

     After her suspension, she returned to my classroom. The student's young mother was trying to raise six children while her husband was away in the war. The mother and I agreed to work together to help her

oldest daughter.

     There were no more incidents of anger the rest of the year. In fact, in the seven years I remained at that school, I taught all six of this family's children. When the youngest was in my class, the mother told me,

"Our family loves you. Every year one of my kids says, 'I hope I'm in her class!'"

     The standard of seeing each of my students as a perfect one was the best teaching tool I had, and led to success.

1. At the beginning of teaching, the author _____.

A. was full of confidence in herself        

B. doubted if she could be a good teacher

C. was sure to win love from her students

D. decided to change her students' life

2. What happened in the author's class one day?

A. A girl fought with two boys.    

B. She was hit by a girl.

C. She hit a girl in the face.        

D. Her class was troubled by several girls.

3. How was the girl punished?

A. She was sent to another class.        

B. She was driven out of school at once.

C. She had to stay at home for a few days.

D. She was beaten heavily by her mother.

4. When the girl returned to school, _____.

A. she apologized to the author            

B. she took her mother to school

C. the author was still angry with her      

D. the author treated her with love

5. It can be inferred from the text that _____.

A. the author got along better with boys  

B. the author tried to let the girl come to her class

C. the girl's mother was very thankful to the author at last

D. all the six kids of the woman are hard to teach

多项选择题