问题 计算题

有一个正方形线框的线圈匝数为10匝,边长为20cm,线框总电阻为1Ω,线框绕OO'轴以10πrad/s的角速度匀速转动,如图,垂直于线框平面向里的匀强磁场的磁感应强度为0.5T,求:

(1)该线框产生的交变电流电动势最大值、电流最大值分别是多少?

(2)线框从图示位置转过60°时,感应电动势的瞬时值是多大?

(3)写出感应电动势随时间变化的表达式。

答案

解:(1)交变电流电动势最大值为Em=2nBLv=2nBLωL/2=nBSω=10×0.5×0.22×10π V=6.28 V

电流的最大值为

(2)线框转过60°时,感应电动势E=Emsin60°≈5.44 V

(3)由于线框转动是从中性面开始计时的,所以瞬时值表达式为e=Emsinωt=6.28sin10πt V

完形填空

第三节:完形填空(共20小题;每小题1.5分,满分30分)

Last night I wrote an article for the school newspaper that described how I feel right now in honest terms. I emailed it to our wonderful  41 , and after she  42 it, she asked a very good question: "Do you want the  43  school body, including our senior class and the teaching  44 to read this?"

That question pretty much  45 my thoughts. I'm not a very  46  person; I tend to let only a few friends know  47 what' s going on in my life. I suppose that's  48 my personality says the opposite to itself, because I'm also an honest person.

Being honest is   49  .It involves taking risks—huge risks—and putting  50   on the edge.   51   to someone can be the hardest thing for you in the world and either lead to the hurt of feelings or  52 friendships. During the course of my life, I' ve experienced  53 .

In positive ways, being honest can be a  54 .Pretending is not only difficult,  55 it' s very tiring. Last year,  56 I discovered that I could be open with two people whom I was already good friends with, the load on my shoulders felt much  57 .Telling someone your  58 feelings is scary; trusting someone  59 your heart and soul is hard. Of course, putting one's feelings into  60 for the general population to read is also rather frightening.

41. A. editor               B. coach                C. e-pal                 D. supervisor

42. A. deleted              B. read                  C. forwarded           D. reserved

43. A. entire               B. junior               C. main                 D. key

44. A. member            B. clerk                 C. staff                  D. fellow

45. A. agreed              B. controlled           C. supported            D. matched

46. A. easygoing          B. shy                  C. optimistic           D. open

47. A. exactly              B. rarely                C. roughly              D. usually

48. A. how                 B. what                C. where               D. when

49. A. exciting            B. simple               C. boring               D. difficult

50. A. everybody          B. yourself             C. somebody           D. myself

51. A. Showing off       B. Opening up          C. Getting down        D. Looking up

52. A. unreliable          B. weaker               C. permanent           D. stronger

53. A. either               B. neither               C. both                  D. nothing

54. A. burden              B. dream               C. goal                  D. release

55. A. but                  B. while                C. also                  D. meanwhile

56. A. in which           B. when                C. during which        D. which

57. A. heavier             B. unpredictable        C. lighter               D. unbearable

58. A. miserable           B. secret                C. strong                D. joyful

59. A. by                   B. via                   C. with                  D. beyond

60. A. reality              B. use                   C. practice              D. print

单项选择题