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问题 多选题

如图所示，不计重力的带电粒子经电场MN加速后进入一有界的匀强磁场中，若保持带电粒子在磁场中做半径恒定为R的半圆周运动，关于带电粒子的比荷

q
m
、加速电压U、磁感就应强度B以及带电粒子运动的周期T的关系，下列说法正确的是（　　）

A．当比荷

q
m
恒定时，电压U越大，粒子运动周期T越小

B．当比荷

q
m
恒定时，不管电压U多大，粒子运动的周期T都不变

C．当比荷

q
m
恒定时，带电粒子比荷q/m越大，磁感应强度B越大

D．当比荷

q
m恒定时，带电粒子比荷q/m越大，磁感应强度B越小

答案

带电粒子在匀强磁场中做匀速圆周运动，由洛伦兹力提供向心力可知：Bqv=m 得R=

mv
qB
  ①

而粒子在电场中被加速，则有：

1
2
mv2=qU ②

将①\②两式联立可得：R=

2U
B
?
m
q
③，带电粒子运行的周期T=
2πm
qB
④

A、B由④知，当比荷

q
m
恒定时，粒子运动的周期与加速电压无关，所以当粒子的比荷一定时，不管加速电压U多大，粒子运动的周期都不变．故A错误，B正确．

C、D当加速电压一定时，由题意半径R也一定，由③式知，比荷

q
m
越大，
m
q
越小，则B越小，故C错误，D正确．

故选BD

完形填空
完形填空。

     Professor Green, known to the world as a scientist, is not only absent-minded but short-sighted as well. His mind is always busy  __1__scientific problems and seldom notices what is going on __2    him.  
     One fine day recently, he went 3 a walk in the countryside, but as  __4 _he has a book in his hand.
When he went out , he began to read his book . He hadn’t gone far_ 5 __he run into a big cow and fell
down. In the  fall, he had lost his glasses, without which he couldn’t see anything. He thought he had hit
his head __6___a fat   lady. “I’m sorry, Madam.” He said politely__7 __searching for his glasses. As
oon as he had___8__, he realized his mistake.
     Soon he was fixing his mind on his book___9__and paid no attention to anything else. He had scarcely
been walking for five minutes when he fell over again, ___10__both his book and his glasses. This time 
he got very     angry, seizing his umbrella, he gave the “cow” a wild blow. Then, after finding his glasses,
he realized with horror that he made a second mistake. A large fat woman was fleeing from him in a horror.

( )1.A. fish     
( )2.A. there    
( )3.A. more     
( )4.A. happened 
( )5A. on       
( )6.A. swimmer  
( )7.A. threw    
( )8.A. deep     
( )9.A. but      
( )10.A. pushing  
( )11.A. place    
( )12.A. seeing   
( )13.A. decided  
( )14.A. while    
( )15.A. turned   
( )16.A. nervous  
( )17.A. wrapped  
( )18.A. save     
( )19.A. on       
( )20.A. boat     


B. boas        
B. it        
B. may         
B. went      
B. within       
B. guard     
B. looked    
B. cool      
B. so           
B. draggig     B. period       B. smiling      
B. went        
B. till        
B. looked       B. afraid       
B. left      
B. thank     
B. out       
B. blanket   


C. was         
C. whe         
C. muh          
C. arrivd       
C. in            
C. soldir       
C. jumd        
C. dirty         
C. and           
C. holdig       
C. secod       
C. lookig       
C. agred        
C. for           
C. hurrid       
C. excitd       
C. placd        
C. wrp          
C. away         C. camea      


D. birds         
D. that          
D. little        
D. came          
D. under         
D. player        
D. turned        
D. cold          
D. or            
D. catching      
D. moment        
D. shouting      
D. promised      
D. as            
D. stood         
D. angry         
D. threw         
D. help          
D. off           
D. screen      

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问答题

某市建筑企业，具有建筑资质和一般纳税人资格。2010年8月发生以下业务：
(1)为本市小学建造校舍，工程施工中耗用自产的建筑材料含税价23.4万元，另收取建筑劳务工程款100万元。合同中已经分别注明材料和劳务工程款；
(2)为本市政府装修政府大楼，工程营业额为270万元，已经开具营业税发票270万元；
(3)为本市工业企业建造职工娱乐厅，按合同约定，由建筑企业外购建筑材料180万元，提供建筑劳务50万元。另为其安装生产设备一台，设备由工业企业购入，购入原价为500万元，安装费20万元；
(4)为本市某歌舞厅提供装饰劳务，取得劳务收入60万元；
要求：根据上述资料，按下列序号计算回答问题，每问要求计算出合计数：
1.建筑企业为小学建造校舍应纳营业税；
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