搜题请搜索小程序“爱下问搜题”
问题 计算题

如图所示，M是一块平面镜，位于透明液体中，镜面水平向上放置，镜面到液面的距离h=0.8m。一束细光线竖直向下射来，通过液体射到平面镜上。现将平面镜以入射点为水平轴顺时针转过18.5°角，转到图中虚线所示的位置，光线经平面镜反射后，在液面处分成两束，且这两束光恰好垂直，求镜面旋转后光从开始进入液面到第一次离开液面的时间。（设平面镜较短，光线在平面镜上只发生一次反射，sin37°=0.6）

答案

8×10-9s

题目分析：将平面镜绕水平轴转过15°角，反射光线将转过30°，反射光线在液面处的入射角等于30°，而反射光在液面处形成的反射光与折射光垂直，画出光路图，根据几何知识求出入射角为i=30°，折射角为r=60°，算出折射率n，结合公式可求出光在液体中的传播速度，再找出光在液体中通过的路程，可求出时间。

依题意作出光路图如图所示当镜面转过18.5°角时，反射光线转过37°角，

即∠AOO′=∠OO′N′=37°，由几何知识可得∠CO′N=53°     （1分）

 

则液体的折射率       ①(2分)

光在液体中的路程为②(1分)

光在液体中的速度     ③(2分)

光从开始进入液面到第一次离开液面的时间④(1分)

由①~④式并代入数据可得t=8×10-9s         (2分)

单项选择题

经批准开山填海整治的土地和改造的废弃土地，从使用的月份起免缴城镇土地使用税5年至10年。具体免税期限由（）确定。

A.省级地方税务局

B.地市级地方税务局

C.县级地方税务局

D.国家税务总局
查看答案
完形填空
完形填空。
     The sound of the rain hitting the windows wakes me up and it sounds just exactly as it did l5 years ago,
which reminded me of my girlhood.
     It was my second day of   1   and it was raining heavily. I could not   2   the habit I had at home, so I fell
asleep right at my   3  . I woke up to find myself not in the classroom but carried on Dad's back. We were 
  4   home. It was the last time I felt   5   to him.
     After that, he never carried me or hugged me as other fathers did to their children. I was not bothered
much by this   6  . I was proud of it. for I felt   7   and "grown up". However,there were times when I felt
depressed by not having searched for   8   from him.
     One day. I was writing Chinese characters as homework. I hated doing this more than anything. Dad
came and stood behind me for a moment,   9   me scratching (勾抹) the paper. Then he said,"This kind of
writing needs  10   .Your writing is not strong enough. Press harder." I followed his   11   for the next two
weeks. but  12   I could see little improvement.
     I followed my own method-the   13   way. His advice did not improve my writing but our  14   . As I grew
older, I found out that he had finished his   15   in Grade 6,which was the highest grade in town then, so he
was considered to be a   16   .People used to ask him to write something to put on the walls. but he never felt
very useful.
     He often said to me," As you can see, this family is going to count on (指望) you. We are   17   to improve
you anything for your future. You have to get   18   to change the life for yourself."
     As a result of his   19   , I have   20   it through high school and through college.
( )1. A. graduation  
( )2. A. develop     
( )3. A. dormitory   
( )4. A. at          
( )5. A. close       
( )6. A. gap         
( )7. A. lonely      
( )8. A. comfort     
( )9. A. guiding     
( )10. A. skill      
( )11. A. introduction
( )12. A. even if    
( )13. A. difficult  
( )14. A. relationship
( )15. A. schooling  
( )16. A. writer     
( )17. A. tired      
( )18. A. an education
( )19. A. help       
( )20. A. succeeded   		B. employment       
B. resist           
B. door             
B. already          
B. near             
B. thought          
B. depressed        
B. help             
B. directing        
B. patience         
B. manner           
B. while            
B. slow             
B. friendship       
B. career           
B. scholar          
B. glad             
B. a rich boyfriend 
B. expectations     
B. got             		C. college       
C. follow        
C. desk          
C. beyond        
C. happy         
C. action        
C. independent   
C. support       
C. watching      
C. time          
C. spirit        
C. as            
C. entertaining  
C. thought       
C. hope          
C. scientist     
C. useless       
C. a well-paid job
C. examination   
C. made          

D. school           
D. break            
D. bed              
D. halfway          
D. relaxed          
D. scene            
D. comfortable      
D. explanation      
D. blaming          
D. practice         
D. advice           
D. though           
D. fast             
D. reality          
D. dream            
D. specialist       
D. ready            
D. a good writing   
D. watch            
D. found            

查看答案