问题 选择题

在如图所示的实验装置中,处在磁极间的A盘和B盘分别是两个可绕不同固定转轴灵活转动的铜盘,实验时用一根导线与A盘的中心和B盘的边缘接触,用另一根导线与B盘的中心和A盘的边缘接触。摇动摇把,A盘顺时针转动(从上往下看)起来后  (    )

A.因穿过A盘的磁通量不变,所以没有感应电流产生

B.A盘上有感应电动势,A盘中心的电势比盘边缘高

C.B盘逆时针转动,B盘中心的电势比盘边缘高

D.B盘顺时针转动,B盘中心的电势比盘边缘低

答案

答案:C

题目分析:转动A盘时,将整个铜盘看成沿径向排列的无数根铜条,它们做切割磁感线运动,产生感应电动势,电路又是闭合的,所以不断转动A盘就可以获得持续的电流.A错误,根据右手定则可得A盘电流方向从内指向外,在电源内部电流从负极流向正极,故边缘的电势大于中心的电势,B错误,根据左手定则可得B盘逆时针转动,B盘中心的电势比盘边缘高,C正确,D错误

点评:动A盘时,将整个铜盘看成沿径向排列的无数根铜条,它们做切割磁感线运动,产生感应电动势,A盘相当于发电机,可以获得持续的电流.而B盘相当于电动机

阅读理解

阅读理解。

     Americans are very direct people. When they want something they say “yes” and when they don’t

they say “no”. If they want something different from what is given, they ask for it.

     Here’s an example. I arrive at someone’s house and he gives me wine, I don’t want wine. Maybe

I don’t like it or maybe I just don’t want it. I will say “No, thanks.” If everyone around me is drinking

something, I would ask for something else, “No, thanks. But I’ll take a bit of tea if you have some.” If

I really want wine, I just say, “Yes, thank you.” Unless they happen to know the Chinese customs,

westerners will not ask you again and again after you have said you don’t want it.

1. If Americans want something, they would say “ _____ " .                

   A. Yes, thank you.                                                      

   B. No, thanks.                                                          

   C. No, I’m sorry.                                                      

   D. Yes, why not.                                                        

2. When Americans do not want what is given, they would say “_____ " .    

   A. No, I don’t.                                                        

   B. No, thanks.                                                          

   C. Yes, thank you.                                                      

   D. No, I’m sorry.                                                      

3. In this passage, “westerners” means_____.                              

   A. the people who live in the west of their country                    

   B. the visitors who go to the Western countries                        

   C. the people who live in the Western countries                        

   D. the people who know the customs of the West                          

4. The Chinese people might _____ if you don’t want something given.      

    A. be glad                                                            

    B. say “thank you”                                                    

    C. get angry                                                          

    D. ask you again to take it                                            

5. From this passage we know that _____ .                                  

   A. the Chinese people are direct                                        

   B. the Chinese customs are better                                      

   C. the westerners are more polite                                      

   D. different countries have different customs                          

填空题