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在废物回收分拣站或冶金工厂里,我们经常可以看到一种特殊的起重机,当光秃秃的大圆盘放在各种金属混杂的杂物堆上,通电后,铁片、铁丝、铁钉等铁料马上被吸引到圆盘上(如图1),被轻松地吊起、运走,断电后,废铁料立刻就掉了下来,省略了分拣、打包等繁杂耗时的程序.看到这,有的同学马上会想:这种起重机为什么通电后会吸引铁质材料?而断电后为什么就不能吸引铁质材料了?起重机上的磁性跟电
In waste recycling stations or metallurgical plants, we often see a special type of crane. When a bare big disc is placed on a pile of various metal hybrid debris heaps of iron, iron wire, iron nails Iron and other materials were immediately attracted to the disc (Figure 1), was easily lifted, shipped away, the power outage, the scrap iron immediately fell down, omitting the sorting, packing and other complex and time-consuming procedures When I saw this, some students immediately wondered why the crane would attract ferrous materials when energized, and why it could not attract ferrous materials after the power was cut off.