英語聽力文摘474 海洋獨特的磁場

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Motional Induction

Last time, we talked about “motional induction,” a phenomenon by which the ocean generates a magnetic field.

It works like this: earth has its own magnetic field. The ocean has plenty of charged atoms in it, in the form of dissolved salt. These atoms are in motion because the ocean flows.

Charged atoms moving through a magnetic field will induce an electric current. And an electric current will, in turn, create another magnetic field. The ocean should generate its own magnetic field.

You said should. How could we know this “motional induction” is happening?

Direct evidence came in 2003 from scientists working at the University of Washington and a research institute in Potsdam, Germany. These researchers used a magnetometer on board an orbiting satellite.

First, they figured out what the magnetic field of the planet should be. After subtracting this figure, they found there was still some leftover magnetic field.

Next, the team made a computer model of what kind of magnetic field the ocean should generate through motional induction. Sure enough, their prediction matched the excess magnetic field measured by the satellite.

The satellite also found that magneticintensity over the oceans peaked every twelve and a half hours, but not over the land. Can you guess why?

Every twelve hours… Oh, I get it— tides!

Exactly right! The tides rise and fall every twelve and half hours, just as that extra magnetic energy swells and diminishes. This is very strong evidence that motional induction is real… and the ocean has its own magnetism.

上次，我們提到過動生電磁感應(yīng)：海洋產(chǎn)生磁場的一種現(xiàn)象。

地球有自己的磁場，海洋有無數(shù)溶解鹽形式的帶電原子，隨著海洋運動而運動。

在磁場中運動的帶電原子會引起電流，而電流反過來又回形成另一個磁場。這樣海洋應(yīng)該就形成了自己的磁場。

你說“應(yīng)該”，我們怎么知道這種動生電磁感應(yīng)確有其事?

直到2003年，華盛頓大學(xué)和德國波茲坦的某研究學(xué)院研究人員將磁力計放在軌道衛(wèi)星上，證實海洋的磁場真是存在。

最初，磁力計上的數(shù)據(jù)讓科學(xué)家以為是地球磁場作用的。

而后，他們發(fā)現(xiàn)除去這個因素后，仍然有磁場存在。

研究人員又電腦模擬在動生電磁感應(yīng)讓海洋產(chǎn)生哪種磁場，當(dāng)然，科學(xué)家的推論和衛(wèi)星上測出的“另一個”磁場吻合。

衛(wèi)星還發(fā)現(xiàn)，海洋磁場每隔12個半小時就會出現(xiàn)高峰，但是地球磁場不受影響。你能猜到原因嗎?

每隔12個半小時?我知道了!答案是潮汐。

完全正確!潮汐每隔12個半小時潮起潮落，正好和“另一個”磁場高低峰吻合。這正是磁場感應(yīng)存在的真憑實據(jù)，海洋確實有自己獨特的磁力。