考研優(yōu)美英語作文背誦009
Electricity
The modern age is an age of electricity. People are so used to electriclights, radio, televisions, and telephones that it is hard to imagine whatlife would be like without them. When there is a power failure, people gropeabout in flickering candlelight, cars hesitate in the streets becausethere are no traffic lights to guide them, and food spoils in silent refrigerators.
Yet, peoplebegan to understand how electricity works only a little more than two centuriesago. Nature has apparently been experimenting in this field for millionsof years. Scientists are discovering more and more that the living worldmay hold many interesting secrets of electricity that could benefit humanity.
All livingcells send out tiny pulses of electricity. As the heart beats, it sends outpulses of record; they form an electrocardiogram, which adoctor can study to determine how well the heart is working. Thebrain, too, sends out brain waves of electricity, which can be recorded inan electroencephalogram. The electric currents generated bymost living cells are extremely small -- often so small that sensitiveinstruments are needed to record them. But in some animals, certain musclecells have become so specialized as electrical generators that they do not workas muscle cells at all. When large numbers of these cells are linked together, the effects can beastonishing.
The electriceel is an amazing storage battery. It can send a jolt of as much as eighthundred volts of electricity through the water in which it lives. (An electric house current is only one hundred twentyvolts.) As many as four-fifths of all the cells in the electric eel's body are specialized for generatingelectricity, and the strength of the shock it can delivercorresponds roughly to the length of its body.
電當(dāng)今時(shí)代是電氣時(shí)代。 人們對(duì)電燈、收音機(jī)、電視和電話早已司空見慣以致很難想 象沒有它們生活會(huì)變成什么樣。
當(dāng)停電時(shí)，人們?cè)趽u曳不定的燭光下暗中摸索； 因沒有紅 綠燈的指示，汽車在道路上遲疑不前；冰箱也停止工作，導(dǎo)致食物變質(zhì)。人們只是在兩個(gè)世 紀(jì)前一點(diǎn)才開始了解電的使用原理，自然界卻顯然在這方面經(jīng)歷過了數(shù)百萬年。 科學(xué)家不 斷發(fā)現(xiàn)許多生物世界里可能有益于人類的關(guān)于電的有趣秘密。所有生物細(xì)胞都會(huì)發(fā)出微小的 電脈沖。
當(dāng)心臟跳動(dòng)時(shí)，把它發(fā)出的脈沖記錄下來就成了心電圖，這可讓醫(yī)生了解心臟的 工作狀況。大腦也發(fā)出腦電波，這可在腦電圖上記錄下來。
許多生物細(xì)胞發(fā)出的電流都是 極微小的，小到要用靈敏儀器才能記錄和測(cè)量。 但一些動(dòng)物的某些肌肉細(xì)胞能轉(zhuǎn)化成一個(gè) 個(gè)發(fā)電機(jī)，以致完全失去肌肉細(xì)胞的功能。
這種細(xì)胞大量地連接在一起時(shí)產(chǎn)生的效果將是 非常令人吃驚的。電鰻就是一種令人驚異的蓄電池。 它可以在水中發(fā)出相當(dāng)于 800 伏特電 壓電流(家庭用戶的電壓只有 120 伏特)。 在電鰻的身體里，多至五分之四的細(xì)胞都專門用 來發(fā)電，而且發(fā)出的電流的強(qiáng)度大約和它身體的長度成正比。
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