问题 选择题

一理想变压器的原线圈A、B两端接入电压为u = 3sin314t V的交变电流。原线圈匝数n1 =100匝,副线圈匝数n2 =200匝,则 (    )

A.将击穿电压为6V的电容器接在C、D两端,能正常工作

B.把电磁打点计时器接在C、D两端,打点周期为0.01s

C.把额定电压为6V的小灯泡接在C、D两端,小灯泡能正常工作

D.把交流电压表接在C、D两端时,电压表读数为8.48V

答案

答案:C

题目分析:由A、B端电压表达式知原线圈电压最大值为 3V,根据理想变压器原副线圈电压比与匝数成正比知副线圈电压最大值为6V,大于电容器击穿电压,故电容器不能正常工作,选项A错误;由表达式知角速度,交流电周期T=,故打点周期为0.02s;根据正弦交流电有效值为最大值的知副线圈电压有效值为6V,故额定电压为6V的小灯泡能正常工作,选项C正确;接在C、D两端的电压表示数也是有效值6V,故选项D错误;

判断题
阅读理解

B

Dear Editor,

I’m a Senior 1 student in a middle school. This term, my favourite teacher, Miss Mao, no longer teaches us. I want to see her, but I’m afraid that she no longer likes me and I don’t want to trouble her. I really miss her. What should I do?

Tian Yan  

Dear Tian Yan,

It’s bad luck that you have lost your favourite teacher. But, if she is still in your school, nothing can stop you going to see her. When she isn’t busy, ask her if she minds having a quick chat. You can then tell her she was your favourite teacher. Everyone is happy to know they are liked!

If she has left the school, it will be more difficult to meet her. It will be hard, but remember people always come and go in our lives. We can’t rely on(依靠) them being with us all the time.

You may be sad to say goodbye to her, but we can remember and learn from her. Think of her best qualities.  

You could also try looking for similar qualities in your other teachers. Study hard and give your new teacher a chance. In time, you might start to see that he or she has different qualities to learn from.

Finally, you can not completely rely on other people getting you through your studies, or even your life.

Editor      

35. Tian Yan ______.

A. is a troublemaker     B. likes Miss Mao very much    

C. is happy these days     D. doesn’t like to tell her secret to anyone

36. Which of the following does the editor advise Tian Yan NOT to do?

A. Find a time to see Miss Mao.     B. Have a short chat with Miss Mao.  

C. Tell Miss Mao she likes her.      D. Keep quiet about the thing.

37. The expression “in time” in this passage means “______”.

A. over a period of time    B. on time        C. at the right time      D. a long time ago

38. According to the passage, students can make progress in their studies ______.

A. completely by their favourite teachers     B. completely by their favourite classmates

C. mainly by their parents                 D. mainly by themselves