问题 多选题

一束光从空气射向折射率n=

2
的某种玻璃的表面,如图所示:i代表入射角,则下列说法错误的是(  )

A.当i>45°时会发生全反射现象

B.无论入射角i是多大,折射角r都不会超过45°

C.欲使折射角r=30°,应以i=45°的角度入射

D.入射光线和反射光线不可能同时存在

答案

1、光从光密介质射入光疏介质中时,才可能发生全反射;光从光疏介质射入光密介质中时,是不可能发生全反射的.所以A错,B正确.

2、由公式

sini
sinr
=n,所以
sini
sin30°
=
2
,所以i=45°.故C正确.

3、有入射光线就会有反射光线.故D错.

故选AD

完形填空

I know I should have told the headmaster at the time. That was my real  36 .

He had gone out of the study for some  37 , leaving me alone. In his absence I looked to see  38  was on his desk. In the  39  was a small piece of paper on which were written the  40  “English Writing Prize 1949. History Is a Serious of Biographies (人物传记)”.

A(n) 41 boy would have avoided looking at the title as soon as he saw the  42 . I did not. The subject of the English Writing Prize was kept a  43  until the start of the exam so I could not 44 reading it.

When the headmaster  45 , I was looking out of the window.

I should have told him what had  46 then. It would have been so  47  to say: “I’m sorry, but I 48  the title for the English Writing Prize on your desk. You’ll have to  49  it.”

The chance passed and I did not  50 it. I sat the exam the next day and I won. I didn’t  51  to cheat, but it was still cheating anyhow.

That was thirty-eight years  52 when I was fifteen. I have never told anyone about it before, 53  have I tried to explain to myself why not.

The obvious explanation is that I could not admit I had seen the title 54  admitting that I had been looking at the things on his desk.  55  there must have been more behind it. Whatever it was, it has become a good example of how a little mistake can trap (使陷入) you in a more serious moral corner (道德困境).

36. A. plan     B. fault   C. grade  D. luck

37. A. reason  B. course C. example     D. vacation

38. A. this      B. which C. that     D. what

39. A. drawer  B. corner C. middle       D. box

40. A. names   B. words C. ideas   D. messages

41. A. honest  B. handsome   C. friendly      D. active

42. A. desk     B. paper  C. book   D. drawer

43. A. question       B. key     C. note    D. secret

44. A. help     B. consider     C. practise      D. forget

45. A. disappeared  B. stayed C. returned     D. went

46. A. existed  B. remained    C. happened    D. continued

47. A. tiring    B. easy    C. important   D. difficult

48. A. saw      B. gave   C. set      D. made

49. A. repeat   B. defend       C. correct       D. change

50. A. take      B. have   C. lose    D. find

51. A. remember    B. learn   C. mean  D. pretend

52. A. past      B. ago     C. then    D. before

53. A. either   B. never  C. nor     D. so

54. A. by B. besides       C. through      D. without

55. A. But      B. Though      C. Otherwise D. Therefore

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