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标题: 急！3月JJRC一题求助！(关于RC-10 修改测量数据) [打印本页]

作者: acacia_hong 时间: 2009-3-8 09:18
标题: 急！3月JJRC一题求助！(关于RC-10 修改测量数据)

原文

In 1975 Chinese survey teams remeasured Mount Everest, the highest of the Himalayan mountains. Like the British in 1852, they used the age-old technique of “carrying in” sea level: surveyors marched inland from the coast for thousands of miles, stopping at increments of as little as a few feet to measure their elevation, and marking each increment with two poles. To measure the difference in elevation between poles, surveyors used an optical level—a telescope on a level base—placed halfway between the poles. They sighted each pole, reading off measurements that were then used to calculate the change in elevation over each increment. In sight of the peaks the used theodolites telescopes for measuring vertical and horizontal angles—to determine the elevation of the summit.

The Chinese, however, made efforts to correct for the errors that had plagued the British. One source of error is refraction, the bending of light beams as they pass through air layers of different temperature and pressure. Because light traveling down from a summit passes through many such layers, a surveyor could sight a mirage rather than the peak itself. To reduce refraction errors, the Chinese team carried in sea level to within five to twelve miles of Everest’s summit, decreasing the amount of air that light passed through on its way to their theodolites. The Chinese also launched weather balloons near their theodolites to measure atmospheric temperature and pressure changes to better estimate refraction errors. Another hurdle is the peak’s shape. When surveyors sight the summit, there is a risk they might not all measure the same point. In 1975 the Chinese installed the first survey beacon on Everest, a red reflector visible through a theodolite for ten miles, as a reference point. One more source of error is the unevenness of sea level. The British assumed that carrying in sea level would extend an imaginary line from the shore along Earth’s curve to a point beneath the Himalaya. In reality, sea level varies according to the irregular interior of the planet. The Chinese used a gravity meter to correct for local deviations in sea level.

Q32

It can be inferred from the passage that

refraction would be most likely to cause

errors in measurements of a mountain’s

elevation under which of the following

conditions?

A. When there are local variations in sea

level

B. When light passes through humid air

C. When theodolites are used relatively far

from the mountain peak.

D. When weather balloons indicate low air

temperature and pressure.

E. When sea level has been carried in to

within five to twelve miles of the summit.

答案是C,jj作者给的是D，但我觉得是C对，看这句 To reduce refraction errors, the Chinese team carried in sea level to within five to twelve miles of Everest’s summit, decreasing the amount of air that light passed through on its way to their theodolites. 而ballon的作用是to measure atmospheric temperature and pressure changes to better estimate refraction errors，和题干中

to cause
errors似乎没什么关系啊。

求助！！

作者: acacia_hong 时间: 2009-3-9 19:00

大家帮忙看看啊！快考了，急~谢谢啊！

作者: cathyzq 时间: 2009-3-9 22:39

我觉得是D，因为是导致错误的原因而不是避免错误的方式。。。

作者: 洛洛luoluo 时间: 2009-3-10 04:09
是refraction cause error的呀。Chinese把仪器带到山顶去，就减少了error。但是不能反过来推说仪器离得远就cause error。关键应该还是stick to文章中temperature和moisture导致refraction--->error吧。题目的cause error还是挺重要的。

作者: hellokelly 时间: 2009-3-10 04:21
my understanding is
The
Chinese also launched weather balloons near their theodolites to
measure atmospheric temperature and pressure changes to better
estimate
refraction errors.

作者: aKisspy 时间: 2009-3-10 08:37
我当时也觉得是C，以前CD上给出过C的结论……我个人还是支持C。看整理RCJJ的楼主说，因为低气压和温度会加大折射，我觉得他用了文章之外的知识解题，似乎过度推理了，而选C就是一个取反。

作者: jikuren 时间: 2009-3-10 11:39
the Chinese team carried in sea level to within five to twelve miles of Everest’s summit
这句话我就没读懂，牛牛能翻译一下么？怎么能够把sea level带到离顶峰5唛之内呢？好奇。。。

作者: jikuren 时间: 2009-3-10 12:32
仔细读了这篇文章，答案是D。
因为文章第2段第2句话就给了REFRACTION的定义：
One source of error is refraction, the bending of
light beams as they pass through air layers of different temperature and
pressure.
推理如果发生气压和温度变化，就可能发生折射。D最直接。
C呢，说的距离太远了会有ERROR。文中讲了距离远=〉气压和温度不同的LAYER多=〉ERROR，还是D.

[此贴子已经被作者于2009-3-10 12:40:15编辑过]

作者: helenwolf 时间: 2009-3-10 18:42
我认为是d,提问是什么情况下会造成错误，只要指出，pressure和temperature的选项就是正确的

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