英語(yǔ)時(shí)差:北極光
Perhaps you've seen pictures of the northern lights. These fiery curtains of light often dance across the night skies in the far north. The northern lights probably seem far away and exotic, but the same process that makes them shine can be found much closer to home. It's happening right now, inside the nearest fluorescent lamp. The northern lights, or aurora borealis, are powered by energy from outer space. Energetic particles from the sun are captured by the Earth's magnetic field and spiral downward toward the poles. When these particles reach Earth's upper atmosphere, they strike the atoms there so strongly that their very electrons begin to shake loose. When electrons are disturbed this way, they can give off light. It's this microscopic turmoil, miles above the Earth's surface, that gives the northern lights their eerie glow. A fluorescent lamp is powered by ordinary, household electric current. This current races through the lamp's glass tube, which is filled with a mixture of gas and mercury vapor at low pressure. When the current passes through this mixture, it jostles the electrons there just as electrons above the poles are jostled by solar particles. This causes the same kind of microscopic turmoil that lights up the arctic skies. Fortunately for us, our supply of household electric current is more uniform and dependable than the erratic energy that powers the northern lights. This makes fluorescent lights much brighter and steadier than their shimmering and shifting cousins above the north pole. They might not be as exotic, but fluorescent lamps help us see to brush our teeth, read the paper, and go about our daily business. So the next time you long for the romance of the northern lights, switch on a fluorescent lamp! You'll lose some of the mystique, but the principle will be the same.
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