英語聽力文摘 電線上的小鳥
Bird on a Wire
當(dāng)我們行走在馬路上時，經(jīng)?？梢钥吹匠扇旱穆槿富驗貘f停落在幾萬伏的高壓電線上，它們不僅不會觸電，而且一個個顯得悠閑自得。可是，你也知道，如果有人不小心碰到高壓線就會觸電身亡!同樣都是一根高壓線，為什么小鳥站在上面卻不會觸電呢? 我們都知道，電分為正負(fù)兩極。在正負(fù)兩極之間連接上導(dǎo)體，電流就會從導(dǎo)體上流過。同樣電線也分為正負(fù)兩根。人體是導(dǎo)體，人的身體較大，在碰到電線時，把兩根電線連在一起，形成短路，人體上就有大電流流過，這就是人觸電身亡的原因。由于小鳥身體較小，它只接觸了一根電線，它的身體和所站在的那根電線是等電位，身體上沒有電流通過，所以它們不會觸電。但是，如果蛇爬到電線上就危險了，它的身體較長，當(dāng)它爬到高壓線上后會把正負(fù)兩根連接在一起造成觸電死亡。
Have you ever wondered why birds aren't (1)electrocuted(使觸電致死) by the currents(電流) that flow through high-voltage power lines(高壓電線)? Find out on this Moment of Science.
It’s not unusual to see lines of birds (2)perched(棲息) on power lines. But did you ever wonder why birds aren’t electrocuted by the enormous currents that flow through these high-voltage wires?
You might think it’s because the wires are (3)insulated(絕緣的), but they’re actually not insulated at all — that’s why downed(擊落的) power lines are so dangerous. No, the only reason why birds on power lines usually aren’t electrocuted is because the wire is the only thing they’re touching!
Like all energy, electricity seeks (4)equilibrium(均衡，平衡), or balance. That means electricity will flow from high-energy areas to areas of less energy, always using the path of least resistance(阻力最小的方向). So if the bird has one foot on our original wire, and the other foot on, for example, the ground or on a different wire with less voltage, the bird would be electrocuted. Because the electricity would pass through the bird on its way from the high-voltage line to the lower-voltage line or the ground.
But as long as both of the bird’s feet are on the same wire (or wires of the same voltage), the bird is safe. The current doesn’t have anywhere else to go, so the electricity won’t pass through the bird–it stays on the path of least resistance, the wire.
This would work for humans, too–if you were to hang suspended from one of these wires, you wouldn’t be electrocuted, as long as you didn’t get too close to anything else, like a lighter or a telephone pole(電話線桿) or the ground. But don’t try this experiment at home! If you want proof, just look up at the birds on the wires!
Notes:
(1)electrocute [i'lektr?kju:t] vt. (美)以電椅處死;使觸電致死
1.Don't touch that wire, you'll electrocute yourself.
別碰那根電線，你會被電死的。
2.The electrocute and disintegrate videos show it pretty well.
瓦解之光和電刑的動畫很好的顯示了這一點。
(2)perch [p?:t?] n. 高位;棲木;桿 vt. 棲息;就位;位于;使坐落于 vi. 棲息;就位;位于
1.A lady was walking to work when she saw a parrot on a perch in front of a pet store.
有一位女士在步行去上班途中，看見一只鸚鵡棲息在一間寵物店前面。
2.To demonstrate, Justin, one of Pepperberg's undergraduate assistants, instructs Griffin and Alex to hop up on the work perch.
為了演示，佩珀堡的一個大學(xué)生助手賈斯廷，指導(dǎo)格里芬和亞歷克斯跳到高處工作架上去。
(3)insulated ['ins?,leit?d] adj.絕緣的;隔熱的 v.使…絕緣(insulate的過去式)
1.Wind an insulated copper wire around a pen.
在一枝筆上纏繞一圈絕緣銅線。
2.Many houses in the north are warm in winter because they are insulated so that the heat is not lost.
北方的許多房子在冬天很暖和，因為它們都作了隔熱處理，使熱量不致散失。
(4)equilibrium [,i:kwi'libri?m] n.均衡;平靜;保持平衡的能力
The equilibrium price decreases but equilibrium quantity increases.
均衡價格減少，但均衡數(shù)量增加。
