问题 选择题

ab两种单色光组成的光束从介质进入空气时,其折射光束如图所示。用ab两束光

A.先后照射双缝干涉实验装置,若在缝后屏上都能出现干涉条纹,则能确定光是横波

B.先后照射某金属,若a光照射时恰能逸出光电子,则b光照射时也能逸出光电子

C.从同一介质以相同方向射向空气,其界面为平面,若b光不能进入空气,则a光也不能进入空气

D.从同一介质以相同方向射向空气,其界面为平面,a光的反射角比b光的反射角大

答案

答案:C

题目分析:根据折射定律可知,a光的折射角较大,所以a光的折射率较大,a光的频率高。

A、不管是横波还是纵波都能出现干涉现象,所以不能由干涉现象判断是横波还是纵波;错误

B、由于发生光电效应必须满足入射光的频率大于等于极限频率,由于a光的频率大于b光的频率,虽然a光能发生光电效应,a光的频率大于极限频率,但b光频率不一定大于极限频率,b光不一定发生光电效应;错误

C、若b光发生全反射,b光的入射角大于临界角,由于a光的折射率大于b光的折射率,则a光的入射角也大于临界角,a光一定发生全反射;正确

D、在同一界面上发生反射,入射角相同,反射角一定相同,与光的频率无关;错误

故选C

点评:根据折射定律可以判断两束光的频率关系、波长关系、临界角关系等等,然后再由相关知识判断现象的正确性。

判断题
阅读理解

Archaeology as a profession faces two major problems. It is the poorest of the poor. Only small sums are available for excavating(挖掘)and even less is available

for publishing the results and preserving the sites once excavated. Yet archaeologists deal with priceless objects every day. Besides, there is the problem of unlawful excavation, resulting in museum-quality pieces being sold to businessmen at the highest price..

I would like to make a suggestion that would at once provide money for archaeology and reduce the amount of diggings against law. You might say that professionals excavate to get knowledge, not money. Moreover, ancient artifacts(古器

物) are part of our global cultural heritage(遗产), which should be there for all to appreciate, not sold at the highest price. I agree. Sell nothing that has scientific value. But, you might reply, everything that comes out of the ground has scientific value. Here,

we disagree. In theory, you may be correct in saying that every artifact has hidden scientific value.

People can not help appreciate every unearthed treasure but there is not enough money even to put the finds in good order; as a result, they cannot be found again and become as inaccessible as if they had never been discovered. Indeed, with the help of the Internet, sold artifacts could be more reachable than are the pieces stored in museum basements. Before sale, each could be photographed and the list of the purchasers could be maintained on the computer. A purchaser could even be required to agree to return the piece if it should become needed for scientific purposes.

小题1:What’s the problems that archaeology as a profession has to face?

A.Money and unlawful excavation

B.Effectively duplicates.

C.Scientific purposes.

D.Excavation law.小题2:To let most people enjoy ancient artifacts, the practical way could be_______.

A.putting them in the museum

B.having sold artifacts returned

C.making use of the Internet

D.solving the money problem小题3:Which of the following four suggestions about archaeology is from the author?

A.No selling of any unearthed ancient artifacts.

B.Some money should be raised for the purpose.

C.Selling some unearthed ancient artifacts and having them returned when needed.

D.Ancient artifacts, our global cultural heritage, should be evenly shared by us all.