问题 选择题

等腰三棱镜ABC的顶角θ=41.30°,一束白光以较大的入射角从棱镜的一个侧面射入,通过棱镜后从另一侧面射出,在光屏上形成由红到紫的彩色光带如图.已知各色光在棱镜中的折射率和临界角如表所示:

色光绿
折射率1.5131.5141.5171.5191.5281.532
临界角41.37°41.34°41.25°41.17°40.88°40.75°
在入射角α逐渐减小到零的过程中,光屏上彩色光带的变化情况是

A.紫光最先消失,最后只剩橙、红光

B.紫光最先消失,最后只剩黄、橙、红光

C.红光最先消失,最后只剩紫、蓝光

D.红光最先消失,最后只剩紫、蓝、绿光

答案

答案:A

当入射角α减小时,进入AB面内的折射角r也减小,射至另一侧面AC上的入射角β则随之增大.当入射角α减小到零时,表示光垂直AB入射,射至AC面上的入射角β′=θ=41.30°.由题中的临界角表可知,此时β′已超过黄、绿、蓝、紫各色光的临界角,表示这四种色光不会从AC面出射.由于紫光的临界角最小,在α减小到零的过程中必将最先消失,所以最后仅剩橙光、红光从AC射出.

单项选择题
阅读理解

阅读下面短文,从每题所给的四个选项中,选出最佳答案。     

A

Part-time Waitress

Busy café needs honest and good-looking waitress for weekends. Must enjoy working with a team and dealing with customers. Call Li Ling at 0732-8536724 after 6 pm.

Delivery (投递) Person

Young, healthy person able to deliver heavy boxes of books. Must have a driver’s license and can carry heavy boxes. We’re looking for a person for this position. Call Liu Fang at 0732-7887766 at any time.

Nanny Wanted

Kind, hard-working nanny wanted to look after three friendly children. Must be experienced and have childcare quail fications(资格). Please call Chen Yiping at 0732-6774538 between 10 a.m. and 4 p.m  

小题1:These are _______ in the newspaper.

A.notices

B.ads

C.stories

D.news小题2:If you can get the job in the café, you must be a _______.

A.pretty young woman

B.good-looking boy

C.cool young man

D.hard-working student小题3:Who can do the delivery job?

A.A beautiful woman who is good at selling books.

B.A person who has been a taxi driver for more than 40 years.

C.A beautiful and hard-working girl.

D.A strong young man who can drive.小题4:Which of the four statements is true?

A.You can call Chen Yiping in the evening.

B.If you want to call Li Ling, do it in the morning.

C.You can call Liu Fang at any time.

D.If you want to call Li Ling, you can do it in the afternoon.小题5:What’s the Chinese for the underlined word “nanny”?

A.奶奶

B.阿姨

C.保姆

D.护士