托福阅读机经背景材料：电线上的鸟

　　Have you ever wondered why birds aren't (1)electrocuted(使触电致死) by the currents(电流) that flow through high-voltage power lines(高压电线)? Find out on this Moment of Science.

　　It’s not unusual to see lines of birds (2)perched(栖息) 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(绝缘的), but they’re actually not insulated at all — that’s why downed(击落的) 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(电话线杆) 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)以电椅处死;使触电致死

　　1.Don't touch that wire, you'll electrocute yourself.

　　别碰那根电线，你会被电死的。

　　2.The electrocute and disintegrate videos show it pretty well.

　　瓦解之光和电刑的动画很好的显示了这一点。

　　(2)perch [p?:t?] n. 高位;栖木;杆 vt. 栖息;就位;位于;使坐落于 vi. 栖息;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，看见一只鹦鹉栖息在一间宠物店前面。

　　2.To demonstrate, Justin, one of Pepperberg's undergraduate assistants, instructs Griffin and Alex to hop up on the work perch.

　　为了演示，佩珀堡的一个大学生助手贾斯廷，指导格里芬和亚历克斯跳到高处工作架上去。

　　(3)insulated ['ins?,leit?d] adj.绝缘的;隔热的 v.使…绝缘(insulate的过去式)

　　1.Wind an insulated copper wire around a pen.

　　在一枝笔上缠绕一圈绝缘铜线。

　　2.Many houses in the north are warm in winter because they are insulated so that the heat is not lost.

　　北方的许多房子在冬天很暖和，因为它们都作了隔热处理，使热量不致散失。

　　(4)equilibrium [,i:kwi'libri?m] n.均衡;平静;保持平衡的能力

　　The equilibrium price decreases but equilibrium quantity increases.

　　均衡价格减少，但均衡数量增加。