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问题 选择题

风速仪的简易装置如图甲所示．在风力作用下，风杯带动与其固定在一起的永磁铁转动，线圈中的感应电流随风速的变化而变化．风速为v1，时，测得线圈中的感应电流随时间变化的关系如图乙所示；若风速变为v2，且v2＞v1，则感应电流的峰值Im、周期T和电动势E的变化情况是（　　）

A．Im变大，T变小

B．Im变大，T不变

C．Im变小，E变小

D．Im不变，E变大

答案

根据EM=NBSω，可知当转速变大时，则最大感应电动势也变大，所以感应电流也变大；

根据转速与周期成反比，可知，当转速变大时，则周期变小．故A正确，BCD错误．

故选A．

阅读理解

书面表达。

Dear Peter,

     Thanks for your last letter. I am happy to know you' had a very great funny vacation. As your best

pen pal, I'd like to tell you how I spent my vacation. I didn't go to school on May 1st and my parents

didn't go to work, so we went to visit Changbaishan. There are many buses to go there. We had a new

car and my mother drove the car there. Changbaishan is really an interesting place. Many people go

there every day. We saw lots of beautiful trees and had lunch under a tall tree. Then we went to Tian

Chi—a fantastic big lake (湖泊)—The water is blue and very clean. But nobody can swim in the water.

It can make it dirty and it is dangerous to swim in it. We took many photos with our camera. At 5: 00

p.m. we went home happily.

                                                                                                                                    Yours,

                                                                                                                                 Wang Qiang

1. Peter and Wang Qiang are ______.     

A. classmates 

B. cousins

C. brothers

D. pen pals

2. When did they go to Changbaishan? 

A. On May 4th.

B. On June l st.

C. On May 1st. 

D. On July 1st.

3. Wang Qiang and his parents ______ to Changbaishan.     

A. took a taxi    

B. took a car

C. took a bus 

D. walked

4. What does the word "drove" mean?     

A. 购买        

B. 推销

C. 讨论             

D. 驾驶

5. Wang Qiang and his parents didn't ______ on Changbaishan. 

A. swim Tian Chi  

B. have lunch

C. see any trees

D. take photos
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选择题

根据玻尔理论，某原子的电子从能量为E的轨道跃迁到能量为的轨道，辐射出波长为l的光．以h表示普朗克常量，C表示真空中的光速，则等于

A．

B．

C．

D．
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