Electromagnetic Waves托福聽(tīng)力原文翻譯及問(wèn)題答案

Electromagnetic Waves托福聽(tīng)力原文翻譯及問(wèn)題答案

一、Electromagnetic Waves托福聽(tīng)力原文：

NARRATOR:Listen to part of a lecture in a physics class.The professor has been discussing electromagnetic waves.

MALE PROFESSOR:So are there are any questions before we continue our discussion of different types of electromagnetic waves?Um,today we'll focus on radio waves,and specifically,very low frequency radio waves.Ah Yes,Tim?

MALE STUDENT:Are you going to talk at all about the difference between radio waves and sound waves?

MALE PROFESSOR:Um,OK.That might be a good place to start,actually.Sound waves are mechanical in nature,right?Ah,they can only originate and spread in places where there is some dense physical medium,like atmosphere,or water.Ah,they result from changes in pressure in that medium,like changes in air pressure.So they can't travel through a vacuum,where there's no dense physical medium.Which is why they can't travel through interplanetary space.

Radio waves,on the other hand,are fundamentally different from sound waves.They are electromagnetic:they result from oscillations of the electromagnetic field and don't need a physical medium.So they,like other types of electromagnetic wave,can travel basically anywhere—through a vacuum or through atmosphere or water.

Now,radio waves can be detected.For example,very low frequency radio waves can be detected with a special type of radio receiver called a very low frequency,radio,or VLF radio.Which can pick up radio waves with very low frequencies,from 3 to 30 kilohertz,which aren't really picked up by a regular household or car radio.So VLF radios pick up VLF radio waves and convert them to sounds we can hear.

Um,on Earth the main source of naturally occurring VLF emissions is lightning,which generates a pulse of radio waves every time it flashes. Ah yes,Laura?

FEMALE STUDENT:Since you almost always get lightning with thunderstorms,we can pick up VLF waves pretty often,right?You just have to wait until there's a thunderstorm…

MALE PROFESSOR:Ah,do you?Have to wait?VLF receivers are very sensitive and VLF mwaves travel very far.So we can pick up emissions from lightning that's far away.So,actually,you can pretty much listen to them all the time,because lightning strikes Earth constantly,about a hundred times per second.Even if there's no lightning where you are,with a VLF radio you can hear the crackling from storms that are thousands of kilometers away.

However,some times of day are better than others for picking up VLF waves.Daytime isn't as good as nighttime,for example.And what’s more,my colleague Dennis Gallagher says—and in my opinion,he's right—he says the best time to listen for them is around sunset or sunrise.That's when there are natural waveguides in the local atmosphere.

FEMALE STUDENT:Did you say waveguide?

MALE PROFESSOR:Yes.A waveguide,usually it refers to a device,like a metal conductor,that's used to guide and direct waves.But waveguides also occur naturally—they make a path for radio waves to follow in our atmosphere.These natural waveguides occur when the Sun is rising or setting,which makes sunrise and sunset good times to pick up VLF emissions.

Now,there are a few different sounds that you can hear on a VLF receiver,because when lightning strikes,the radio waves travel different distances and in different ways before they reach the receiver.

Some really interesting ones are called“whistlers.”Whistlers come from lightning-generated radio waves that leave Earth's atmosphere and travel into Earth's magnetosphere before bouncing back down.Not all radio waves do this.And the sound they make…well we call them“whistlers”because they sound like slowly descending tone…and no two whistlers are alike—uh,to me they're the most intriguing.

Ah,another interesting sound is the“tweek.”Tweeks are the result of VLF waves that have traveled a long distance through the waveguides.They produce a chirpy sound because the higher–frequency parts of the wave reach the radio receiver before the lower–frequency parts.The entire wave is still considered very low frequency—it's just that some parts of the wave have lower frequencies than others.OK?

二、Electromagnetic Waves托福聽(tīng)力中文翻譯：

旁白：在物理課上聽(tīng)一節(jié)課的一部分。教授一直在討論電磁波。

男教授：在我們繼續(xù)討論不同類型的電磁波之前，還有什么問(wèn)題嗎？嗯，今天我們將重點(diǎn)討論無(wú)線電波，特別是極低頻無(wú)線電波。啊，是嗎，蒂姆？

男學(xué)生：你打算談?wù)劅o(wú)線電波和聲波的區(qū)別嗎？

男教授：嗯，好的。實(shí)際上，這可能是一個(gè)很好的開(kāi)始。聲波本質(zhì)上是機(jī)械波，對(duì)嗎？啊，它們只能在有致密物理介質(zhì)的地方產(chǎn)生和傳播，比如大氣或水。啊，它們是由介質(zhì)中壓力的變化引起的，就像空氣壓力的變化一樣。所以它們不能穿過(guò)真空，因?yàn)槟抢餂](méi)有致密的物理介質(zhì)。這就是為什么他們不能穿越行星際空間。

另一方面，無(wú)線電波與聲波有著根本的不同。它們是電磁的：它們是電磁場(chǎng)振蕩的結(jié)果，不需要物理介質(zhì)。因此，就像其他類型的電磁波一樣，它們基本上可以通過(guò)真空或大氣或水傳播到任何地方。

現(xiàn)在，可以檢測(cè)到無(wú)線電波。例如，可以使用一種稱為甚低頻、無(wú)線電或VLF無(wú)線電的特殊類型的無(wú)線電接收器來(lái)檢測(cè)極低頻無(wú)線電波。它可以接收頻率非常低的無(wú)線電波，從3千赫茲到30千赫茲，而普通的家用或車(chē)載收音機(jī)無(wú)法接收到。所以甚低頻無(wú)線電接收甚低頻無(wú)線電波并將其轉(zhuǎn)換為我們能聽(tīng)到的聲音。

嗯，在地球上，自然產(chǎn)生的甚低頻輻射的主要來(lái)源是閃電，每次閃電都會(huì)產(chǎn)生無(wú)線電波脈沖&nbsp；啊，是嗎，勞拉？

女學(xué)生：因?yàn)槔子陼r(shí)幾乎總是有閃電，所以我們可以經(jīng)常探測(cè)到VLF波，對(duì)嗎？你只要等到有雷雨…

男教授：啊，你呢？必須等待嗎？甚低頻接收機(jī)非常靈敏，甚低頻微波傳播距離非常遠(yuǎn)。所以我們可以收集遠(yuǎn)處閃電的輻射。所以，實(shí)際上，你幾乎可以一直聽(tīng)他們說(shuō)話，因?yàn)殚W電不斷地?fù)糁械厍?，大約每秒100次。即使你所在的地方?jīng)]有閃電，通過(guò)VLF無(wú)線電，你也可以聽(tīng)到數(shù)千公里外風(fēng)暴的噼啪聲。

然而，一天中的某些時(shí)間比其他時(shí)間更適合拾取VLF波。例如，白天不如夜間好。此外，我的同事丹尼斯·加拉赫（DennisGallagher）說(shuō)，在我看來(lái)，他是對(duì)的，他說(shuō)聽(tīng)他們講話的最佳時(shí)間是日落或日出前后。這就是當(dāng)?shù)卮髿庵写嬖谔烊徊▽?dǎo)的時(shí)候。

女學(xué)生：你說(shuō)的是波導(dǎo)管嗎？

男教授：是的。波導(dǎo)管，通常是指一種設(shè)備，如金屬導(dǎo)體，用于引導(dǎo)和引導(dǎo)波。但波導(dǎo)也是自然產(chǎn)生的，它們?yōu)闊o(wú)線電波在大氣層中的傳播開(kāi)辟了一條路徑。這些自然波導(dǎo)發(fā)生在太陽(yáng)升起或落下時(shí)，這使得日出和日落都是接收VLF發(fā)射的好時(shí)機(jī)。

現(xiàn)在，你可以在甚低頻接收器上聽(tīng)到一些不同的聲音，因?yàn)楫?dāng)雷擊時(shí)，無(wú)線電波在到達(dá)接收器之前以不同的方式傳播不同的距離。

一些真正有趣的被稱為“哨子”哨聲來(lái)自閃電產(chǎn)生的無(wú)線電波，這些無(wú)線電波離開(kāi)地球大氣層，進(jìn)入地球磁層，然后反彈回來(lái)。并非所有無(wú)線電波都能做到這一點(diǎn)。他們發(fā)出的聲音…我們稱他們?yōu)椤吧诼暋?，因?yàn)樗麄兟?tīng)起來(lái)像是緩慢下降的音調(diào)…沒(méi)有兩個(gè)哨聲是一樣的，呃，對(duì)我來(lái)說(shuō)，他們是最有趣的。

啊，另一個(gè)有趣的聲音是“tweek”TWEEK是VLF波穿過(guò)波導(dǎo)長(zhǎng)距離傳播的結(jié)果。它們產(chǎn)生啁啾聲，因?yàn)椴ǖ母哳l部分先于低頻部分到達(dá)無(wú)線電接收器。整個(gè)波仍然被認(rèn)為是非常低的頻率，只是波的某些部分的頻率比其他部分低。好啊

三、Electromagnetic Waves托福聽(tīng)力問(wèn)題：

Q1:1.What does the professor mainly discuss?

A.Methods of converting radio waves into sound waves

B.Features of different types of electromagnetic radiation

C.The various paths that very-low-frequency waves follow on Earth

D.The emission and detection of very-low-frequency waves

Q2:2.What is one difference between radio waves and sound waves that the professor emphasizes?

A.Radio waves have a lower frequency.

B.Water stops radio waves from spreading but does not stop sound waves

C.Unlike sound waves,radio waves can travel outside Earth's atmosphere.

D.Naturally occurring radio waves are difficult to detect on Earth at night.

Q3:3.What explanation does the professor give for the constant occurrence of VLF emissions on Earth?

A.At any given time,some part of the world is experiencing sunrise or sunset.

B.Waveguides constantly form in the atmosphere.

C.Earth's magnetosphere directs interplanetary waves toward Earth's surface.

D.Lightning occurs constantly on the planet.

Q4:4.Why are sunrise and sunset the best times to listen to VLF signals?

A.Because thunderstorms are most likely to occur then

B.Because radio waves travel through natural waveguides then

C.Because higher-frequency signals are less active then

D.Because temperatures are not extremely high or low then

Q5:5.Why does the professor discuss whistlers and tweeks?

A.To illustrate that the path a VLF wave travels can affect the sound it makes on a radio

B.To point out that VLF waves can affect the sounds heard on a household or car radio

C.To describe how a colleague discovered the origin of VLF waves

D.To clarify the difference between VLF waves and other kinds of waves

Q6:6.Replay:What does the professor imply when he says this:

A.He needs to think before he can answer the woman's question.

B.The woman has underestimated how often VLF waves can be detected.

C.The woman does not realize that waiting for a thunderstorm can take a long time.

D.The woman does not understand the relationship between thunderstorms and lightning.

四、Electromagnetic Waves托福聽(tīng)力答案：

A1:正確答案：D

A2:正確答案：C

A3:正確答案：D

A4:正確答案：B

A5:正確答案：A

A6:正確答案：B

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