【转】2012人大复试英语笔试阅读理解第三篇题目及答案

[复制链接]

allenkaoyan

8 主题	0 好友	1391 积分

法硕少校

Rank: 8 Rank: 8

该用户从未签到

金币: 355 枚
积分: 1391 点
帖子: 155

发消息

电梯直达

1^#

发表于 2012-3-28 09:17:56 |只看该作者 |倒序浏览

Passage Three
In the early years of the twentieth century, astrophysicists turned their attention to a special category of stars, known as cepheid (辐射点在仙王(星)座中的流星) variables. A variable star is one whose apparent brightness changes from time to time. Among some variables, the change in brightness occurs so slowly as to be almost imperceptible; among others, it occurs in sudden, brief, violent bursts of energy. Cepheid variables have special characteristics that make them a useful astronomical tool.
It was Henrietta Leavitt, an astronomer at the Harvard Observatory, who first examined the cepheid variables in detail. She found that these stars vary regularly in apparent brightness over a relatively short period of time - from one to three days to a month or more. This variation in brightness could be recorded and precisely measured with the help of the camera, then still a new tool in astronomy.
Leavitt also noticed that the periodicity of each cepheid variable - that is, the period of time it took for the star to vary from its brightest point to its dimmest, and back to its brightest again—corresponded to the intrinsic or absolute brightness of the star. That is, the greater the star's absolute brightness, the slower its cycle of variation.
Why is this so? The variation in brightness is caused by the interaction between the star's gravity and the outward pressure exerted by the flow of light energy from the star. Gravity pulls the outer portions of the star inward, while light pressure pushes them outward. The result is a pulsating, in-and-out movement that produces increasing and decreasing brightness. The stronger the light pressure, the slower this pulsation. Therefore, the periodicity of the cepheid variable is a good indication of its absolute brightness.
Furthermore, it is obvious that the more apparent brightness of any source of light decrease the further we are from the light. Physicists had long known that this relationship could be described by a simple mathematical formula. If we know the absolute brightness of any object - say, a star - as well as our distance from that object, it is possible to use the inverse square law to determine exactly how bright that object will appear to be.
This laid the background for Leavitt's most crucial insight. As she had discovered, the absolute brightness of a cepheid variable could be determined by measuring its periodicity. And, of course, the apparent brightness of the star when observed from the earth could be determined by simple measurement. Leavitt saw that with these two facts and the help of the inverse square law, it would be possible to determine the distance from earth of any cepheid variable. If we know the absolute brightness of the star and how bright it appears from the earth, we can tell how far it must be.
Thus, if a cepheid variable can be found in any galaxy, it is possible to measure the distance of that galaxy from earth. Thanks to Leavitt's discovery, astronomical distances that could not previously be measured became measurable for the first time.
31 .The primary purpose of the passage is to explain
A. the background and career of the astronomer Henrietta Leavitt
B. how and why various categories of stars vary in brightness
7
C. important uses of the camera as an astronomical tool
D. how a particular method of measuring astronomical distances was created32. According to the passage, the absolute brightness of a cepheid variable ____.
A. depends upon its measurable distance from an observer on earth
B. may be determined from the length of its cycle of variation C. changes from time to time according to a regular and predictable pattern
D. indicates the strength of the gravitation force exerted by the star
33. Which of the following did Leavitt's work provide astronomers with the means of determining?
A. The absolute brightness of any observable cepheid variable.
B. The apparent brightness of any object at a given distance from an observer.
C. The distance from earth of any galaxy containing an observable cepheid variable.
D. Both A and C.34. Cepheid variable of great absolute brightness would probably exhibit ____.
A. a relatively rapid variation in brightness
B. a correspondingly weak gravitational force
C. slow and almost invisible changes in brightness
D. a strong outward flow of light pressure35. The passage implies that Leavitt's work on cepheid variables would not have been possible without the availability of____.
A. the camera as a scientific tool B. techniques for determining the distances between stars
C. a method of measuring a star's gravitational force
D. an understanding of the chemical properties of stars

复试英语, century, attention, category, special