问题 选择题

在竖直方向的匀强磁场中,水平放置一个面积不变的单匝金属圆线圈,规定线圈中感应电流的正方向如图甲所示,取线圈中磁场B的方向向上为正,当磁场中的磁感应强度B随时间t如图乙变化时,以下四图中正确表示线圈中感应电流变化的是

答案

答案:A

解答:解:在0-内,根据法拉第电磁感应定律,E===.根据楞次定律,感应电动势的方向与图示箭头方向相反,为负值;在-T内,根据法拉第电磁感应定律,

E′===.根据楞次定律,感应电动势的方向与图示方向相反,为负值.且电流为0-内的2倍,故A正确

故选A

点评:解决本题的关键掌握法拉第电磁感应定律E=n=n,会根据楞次定律判断感应电动势的方向.

解答题
完形填空
完形填空
     She walked into the room and his eyes lit up.  
     She didn't have to say a word.  Just being there was a proof enough to show that she __1__ him.  
They had both __2__ someone they loved.  So this day,   of all days,   was a __3__ one.  She wanted
to make this work.  She was hurt,   __4__ and afraid.  It wasn't supposed to be this way.  
     But the fact was that he knew how she felt.  There was an obvious __5__ in his heart,   too.  So the
one thing that __6__ their love for each other was heartache-the most sorrowful kind.  
     Their eyes locked.  He __7__ and she responded.  He had a special way of __8__ a smile to her
face.  She stood there in the doorway and he motioned(示意) to her to sit next to him.  Not __9__ the
childish grin he now had on his face,   she hesitated for a moment,   but  10  .  There was an awkward
moment of silence between them.  
      Then suddenly he    11   behind the pillow placed strategically nearby.  He pulled out a large red 
  12   and nervously handed it to her.  She snapped back with a look of   13   because she really hadn't
expected this.  
     "Wait,   this   14   with it,   " he said.  Then he handed her a small box,   15   perfectly in white tissue
paper of hearts and flowers.  
     "Now,   " he said,   "   16   the card. "
      It reads as follows:
     I know that Valentine's Day is a   17   day for people in love.  I am sure that you would rather
be out at a   18   dinner,   I'm sorry.  But I want you to know thatI love you.  I am so sorry
that   Dad  19   us,   Mom.  But I just wanted you to know we    20   have each other.  
     Happy Valentine's Day!
      Love,  
    Your son,  Adam
( )1. A. loved        
( )2. A. remembered  
( )3. A. hopeless    
( )4. A. uneasy      
( )5. A. puzzle      
( )6. A. influenced  
( )7. A. smiled      
( )8. A. creating    
( )9. A. recognizing  
( )10. A. gave in    
( )11. A. moved      
( )12. A. letter      
( )13. A. sympathy    
( )14. A. remains    
( )15. A. placed      
( )16. A. accept      
( )17. A. special    
( )18. A. rich        
( )19. A. deserted    
( )20. A. still      
B. doubted    
B. found      
B. difficult  
B. angry      
B. pain        
B. broke      
B. questioned  
B. causing    
B. trusting    
B. spoke out  
B. turned      
B. envelope    
B. delight    
B. appears    
B. covered    
B. read        
B. happy      
B. fancy      
B. missed      
B. already    
C. expected  
C. lost      
C. cloudy    
C. bored      
C. regret    
C. blocked    
C. joked      
C. bringing  
C. noticing  
C. helped out
C. pulled    
C. card      
C. surprise  
C. goes      
C. hidden    
C. open      
C. precious  
C. delicious  
C. supported  
C. even      
D. respected    
D. met          
D. memorable    
D. lonely        
D. hope          
D. strengthened  
D. called        
D. removing      
D. enjoying      
D. stepped up    
D. reached      
D. flower        
D. horror        
D. comes        
D. wrapped      
D. spread        
D. fine          
D. pleasant      
D. left          
D. otherwise