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1.接通电池的时间不宜过长。因为这种接法实为短路,时间过长对电池有严重损伤;另外长时间通电会把铁芯磁化,当演示“电磁铁
1. Connect the battery should not be too long. Because this connection is actually a short circuit, the battery is too long for a serious injury; the other will be the power of the core magnetization for a long time, when the demonstration "electromagnet