Official 03 Set 6

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  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
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Spectroscopy

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
What is the lecture mainly about?
  • A. Different ways of magnifying the spectrum of a star

  • B. How a chemical element was first discovered on the Sun

  • C. How astronomers identify the chemical elements in a star

  • D. Why the spectra of different stars are composed of different colors

显示答案 正确答案: C
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    NARRATOR:Listen to part of a lecture in an astronomy class.

    MALE PROFESSOR:Now astronomy didn't really, uh, balloon, into the science it is today until the development of spectroscopy.

    Spectroscopy is basically the study of spectra and spectral lines of light, and specifically for us, the light from stars.It makes it possible to analyze the light emitted from stars.When you analyze this light you can figure out their distance from the Earth and identify what they’re made of—determine their chemical composition.

    Before we get into that, though, it’s probably a good thing to back up a bit.You all know how when you take a crystal prism and pass a beam of sunlight through it, you get a spectrum which looks like a continuous band of rainbow colors.The light that we see with our human eyes as a band of rainbow color falls in the range of what's called visible light.And visible light spectroscopy is probably the most important kind of spectroscopy.Anyone wanna take a stab at the scientific term for visible light… and I'm sure all of you know this because you all did the reading for today…[clearing throat indicating sarcasm]

    FEMALE STUDENT:[confident] Optical radiation. [hesitant] But I thought being exposed to radiation's dangerous.

    MALE PROFESSOR:Yes and no.If you're talking about radiation like in the element uranium, yeah, that's dangerous, but radiation as a general term actually refers to anything that spreads away from its source, so optical radiation is just visible light energy spreading out.

    OK, so we've got a spectrum of a beam of sunlight and it looks like the colors bleed into each other, uh, there’re no interruptions, just a band flowing from violet to green to yellow to…you get the idea.Well what happens if the sunlight spectrum is magnified? [pause - then slightly under breath] Maybe you all didn't do the reading.Well here's what you’d see:I want you to notice that this spectrum is interrupted by dark lines, called spectral lines.If you really magnified the spectrum of the sunlight, you could identify more than a hundred thousand of 'em.They may look kinda randomly placed, but they actually form many distinct patterns.And if you were looking at the spectrum of some other star, the colors would be the same, but the spectral lines would break it up at different places, making different patterns.Each pattern stands for a distinct chemical element, and so different sets or patterns of spectral lines mean that the star has a different chemical composition.

    FEMALE STUDENT:So, how do we know which spectral patterns match up with which elements?

    MALE PROFESSOR:Well, a kind of spectroscopic library of elements was compiled using flame tests.A known element, uh, say a piece of iron for example, is heated in a pure gas flame. The iron eventually heats to the point that it radiates light.This light is passed through a prism, which breaks it up into a spectrum, and a unique pattern, kind of like a chemical fingerprint, of spectral lines for that element appears.This process was repeated over and over again for many different elements.So we can figure out the chemical makeup of another star by comparing the spectral pattern it has to the pattern of the elements in the library.

    Oh! An interesting story about how one of the elements was discovered through spectroscopy.There was a pretty extensive library of spectral line patterns of elements even by the 1860’s.A British astronomer was analyzing a spectrograph of sunlight and he noticed a particular pattern of spectral lines that didn’t match anything in the library.So, he put two and two together and decided there was an element in the Sun that hadn't been discovered here on the Earth yet.Any guesses about what that element is?It’s actually turned out to be pretty common and I'm sure all of you know it.[pause] OK. Let's try something else…Any of you happen to be familiar with the Greek word for sun, by chance?

    MALE STUDENT:Something like helios or something like that?…Oh! It must be "Helium". So you're sayin that helium was discovered on the Sun first?MALE PROFESSOR:Yes. And this is a good example of how important spectroscopy is in astronomy.

  • 旁白:请听一段天文学课上的讲话。

    教授:如今,直到光谱学发展起来了天文学才成为真正的科学。

    光谱学基本上是针对光谱的研究,光谱光线,而特别对我们而言,还有行星发出的光芒。这使得我们分析从行星发出的光芒有了可能性。当你分析这种光线的时候,你可以得出其从地球到该行星的距离,分析他们的构成,决定了他们的化学成分。

    在我们讨论这个之前,我们最好是回顾一下之前学过的。你们都知道,当你拿出一条水晶棱柱通过一束太阳光的时候,你会看到一道光谱,看起来就是一束连续的彩虹色彩斑带。我们肉眼所看到的彩虹斑带将集合成一系列可见光。而可见光光谱很可能是光谱中最为重要的一类。有同学想尝试说一些可见光的科学术语吗?我敢肯定你们都已经知道了一些,因为你们今天都已经读了文章了。

    学生:光辐射。但是我觉得暴露在辐射中是有危险的。

    教授:你说的对,也不对。如果你是说辐射,像铀元素,是的,那就是危险的,但是一般来说,辐射事实上指的是那些从物质原散发出来的东西,而光辐射只是可见光能源发散出来的而已。

    那么,我们已经得到了一束阳光的光谱,看起来就像是色彩都相互融合起来一样。色彩之间没有中断迹象,就是一条色带,从紫色到绿色再到黄色。知道吧。那么,如果太阳光谱扩大了会发生什么呢?也许你们还没有阅读。嗯,这是你们会看到的。我要你们知道的是,光谱会被一种叫做光谱线的黑色线条所阻隔。如果你真的把太阳光线扩大的话,你会分辨出十万多条光谱线。他们看起来像是随机排列,但是事实上他们组成很多不同的图案。而如果你观察一下其他星星的光谱,他们的色彩是一样的。而光谱线会在不同地方将其分割,形成不同的图案。每一种图案都代表了一种不同的化学元素。所以光谱线的不同组合或图案意味着该星星的化学成分也不同。

    学生:那么我们怎么知道哪些光谱图案跟哪些化学元素相匹配呢?

    教授:嗯,我们有一种通过火燃测试收集起来的元素光谱合集。一种众所周知的元素,比如一块铁,会放在纯粹的气焰中加热。铁块会一直加热,直到到达某一燃点,便会辐射出光来。光线穿过一块棱柱,棱柱将光线分割形成光谱,而一种独特的图案便会出现,这种图案就像是某种元素光谱线的化学印记。而很多元素都会经历这样的过程,循环往复。这样我们就可以通过将某元素的光谱图案和光谱合集中的光谱图案进行比较,我们可以获得其他行星的化学成分。

    哦,现在讲一个有趣的故事。这是关于我们是怎么通过光谱学发现某一种元素的。早在十九世纪六十年代的时候,我们便有广泛的关于各元素图案的光谱线合集。当时以为英国的天文学家正在分析一道阳光的光谱图,而他注意到了一种特别的光谱线图案,该图案跟合集中的任何材料都不匹配。所以他将所有元素两两对应并得出结论,太阳中肯定有一种元素是在地球上还没发现的。你们猜得到是什么元素吗?事实上,这种元素非常平常,我敢肯定你们都知道。Ok,我们讨论一下一些其他的把。你们中有没有人碰到过希腊语中的太阳一词?

    学生:是不是像“Helius”或是相类似的。哦,肯定是氦。你的意思是说氦是在太阳上首次发现的?教授:是的。光谱线在天文学中很重要,这就是一个很好的例子。

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  • 本题对应音频:
    3 感谢 6 不懂
    音频1
    解析

    题型分析:主旨题

    原文定位

    When you analyze this light you can figure out their distance from the Earth and identify what they’re made of—determine their chemical composition.

    选项分析

    通过观察光,可以确定物质的化学组成。接下来的文章一直在讲如何分别star中的chemical composition,对应C选项。

    A选项,magnifying是细节。B选项,是细节。D选项,未提及。

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