问题 选择题

如图,为一半圆形的玻璃砖,C为AB的中点,ab两束不同频率的单色可见细光束垂直AB边从空气射入玻璃砖,且两束光在AB面上入射点到C点的距离相等,两束光折射后相交于图中的P点,以下判断正确的是

A.在真空中,a光的传播速度大于b光的传播速度

B.在真空中,a光的波长大于b光的波长

C.a光通过玻璃砖的时间大于b光通过玻璃砖的时间

D.若ab两束光从同一介质射入真空过程中,a光发生全反射的临界角大于b光发生全反射的临界角

答案

BD

分析:由题意:两束光折射后相交于图中的P点,可知玻璃砖对b束光的偏折角大于对a束光的偏折角,则玻璃砖对b束光的折射率大于对a束光的折射率,b光的频率高,波长短,由v= 得到光在玻璃砖中的速度关系,判断出时间关系.由临界角C的正弦sinC= 分析临界角大小.

解:A、所有色光在真空传播相同,为c.故A错误.

B、由题分析可知,玻璃砖对b束光的折射率大于对a束光的折射率,b光的频率高,由c=λf得知,在真空中,a光的波长大于b光的波长.故B正确.

C、由v=得到,a光在玻璃砖中的速度大,a光通过玻璃砖的时间短.故C错误.

D、由sinC=分析得知,a光的折射率n小,a光发生全反射的临界角大于b光发生全反射的临界角.故D正确.

故选BD.

阅读理解

Dogs can be worried and pessimistic just like people, researchers report in a new study in Current Biology. And they aren’t talking about basset hounds (短脚猎狗): those dogs just look as if they expect the worst.

What the scientists say is that dogs that exhibit anxiety when left home alone by their owners may have bigger problems — they may be in a permanent bad mood.

This pessimistic outlook may not otherwise be easily apparent in a dog’s other characteristics, like running speed or learning ability, the study reports.

Dogs are similar to humans in the role that emotional state plays in decision making, said Michael Mendel, a veterinary scientist at the University of Bristol and the study’s lead author. The study’s researchers looked at 24 dogs in shelters in Britain.

They placed the dogs in isolated settings and observed their reactions — many barked, jumped on furniture and scratched at the door.

Then they placed bowls in two rooms. One bowl contained food, while another was empty. After training the dogs to understand that bowls can sometimes be empty, and sometimes full, they began to place bowls in ambiguous locations.

Dogs that quickly raced to the locations were more optimistic, and in search of food. Those that did not were deemed pessimistic.

The more separation anxiety a dog expressed while in isolation, the more likely the dog was to have a pessimistic reaction, the researchers found.

The study carries an important message for dog owners, Dr. Mendel said.

Dogs that express serious anxiety when alone may need treatment, as it could be a sign of unhappiness and instability.

小题1:This passage can be classified as _________.

A.an advertisement

B.a feature story

C.a news report

D.a book review小题2: In the study, many dogs barked, jumped and scratched because __________.

A.they couldn’t find the bowl with food in it

B.they were left alone

C.they needed to be treated

D.they wanted to be active and optimistic小题3:According to Dr. Mendel, which statement is true?

A.Like humans, dogs are good at decision making.

B.Dog owners should train dogs to find food.

C.Emotional state works sometimes when humans make decision.

D.Dogs can always find the bowl with food quickly.小题4:What can we learn from the passage?

A.Dogs will be optimistic as long as they are left alone.

B.Dogs must be in a permanent bad mood when their owners left.

C.Dogs that express anxiety don’t need treatment.

D.Dogs may easily show their pessimistic outlook in learning ability.

单项选择题