用水彩笔在磨砂电灯泡的侧面画一个图案，然后把电灯泡接到电路中让其发光，拿一个凸透镜在灯泡图案与其正对的白墙之间（图案与白墙之间距离较大）移动，则所画图案在墙上成清晰像的情况是（ ）
A．不能成像
B．能成一次像，是放大、正立的虚像
C．能成两次像，一次是放大、倒立的实像，一次是缩小、倒立的实像
D．能成三次像，一次是缩小、倒立的实像，一次是等大、倒立的实像，一次是放大、倒立的实像
灯泡在墙壁上成的像一定是实像，故排除了AB两个选项．
当物距大于二倍焦距时，此时所成的像为倒立的缩小的实像，像距大于一倍焦距，小于二倍焦距．且此时的物距与像距之和大于四倍焦距．
成等大的像的条件是u=v=2f，物距等于2倍焦距时，像距也要等于2倍焦距才能找到像，即u+v=4f，而本题中墙壁与图案之间的距离较大，若成倒立缩小或倒立放大的像，总距离应大于4f，故此种情况不合题意．
当物距小于二倍焦距大于一倍焦距时，此时成一个倒立的放大的实像．
综上分析故选C．
| 先通读下面短文，掌握其大意，然后从各小题所给四个选项中，选出一个最佳答案。 |
| I am sitting in an empty football field after my last high school football game that finished a few hours ago. I'm the mid-field player on my team. But in fact that's not (1) now. I was the mid-field player because, as I said, this was my (2) game. That's a good way to end a high school football career (生涯), especially if you win, but even though you don't, it's (3) to leave at a high point. I was eight when I first started playing football. My dad (4) football, and he used to practise with me at home — passing, catching, running. We used to practise almost every evening (5) it got too dark. He tried to teach everything he knew about the (6). "Just remember: don't ever (7)." "Stay in the game. Don't lose your concentration (专注).""Go out there and give 110 percent(百分之……)every time." Well, that was a long time ago, but I still hear his words (8) in my ears. I had a lot on my mind (9) the game today. I don't like things to end, I guess, and this was the last game. I was talking to myself and warning myself about what to do and not to do. I didn't sleep at all (10), and when the sun came up this morning, I reached the point where (11) just wanted it all to be over, finished, done. But then when the game started, my mind became (12). I just lived in this game, this moment. I didn't hear the crowd, I didn't feel the cold or the pain, I never felt tired. I just kept my eyes on the (13), and it was just me and the ball and, inside, a soft, white light (14) me the way to, and it was a beautiful, empty feeling. It's all over now, and it's really getting cold here. It's starting to snow. The sun's almost gone, and I can (15) see the goal. Now it's dark and I'm sitting here all alone. Well, I guess it's time to say good-bye and move on. |
| ( )1. A. true ( )2. A. first ( )3. A. good ( )4. A. needed ( )5. A. until ( )6. A. football ( )7. A. grow up ( )8. A. ringing ( )9. A. from ( )10. A. tonight ( )11. A. we ( )12. A. empty ( )13. A. way ( )14. A. sending ( )15. A. already | B. wrong B. last B. bad B. hated B. when B. game B. catch up B. saying B. before B. yesterday B. they B. full B. field B. teaching B. hardly | C. strange C. worst C. lucky C. missed C. unless C. goal C. give up C. falling C. through C. today C. I C. rough C. ball C. pointing C. never | D. clear D. favourite D. painful D. loved D. although D. score D. hurry up D. coming D. after D. last night D. he D. awake D. match D. showing D. clearly |