田田想找表哥一起下棋,到了他家后,她看到表哥手里拿着一节电池,电池下面有一枚螺丝钉在不停地转动(如图1)。田田很好奇,她瞪大眼睛仔细看,表哥手里除了一节电池、一根铜丝、一枚螺丝钉外,还有一块柱形的磁铁,磁铁也和螺丝钉一起在转动。简单几样东西就能这么神奇,奥秘在哪呢?她猜想:“可能是因为有磁铁的缘故吧。”于是,她把东西都拿过来,将电池、螺丝钉和磁铁直接连接起 Tada to find cousin to play chess, to his home, she saw a cousin in his hand holding a battery, the battery has a screw under the constant rotation (Figure 1). Tada is very curious, she stared at her eyes wide open, cousin in addition to a battery, a copper wire, a screw, there is a cylindrical magnet, the magnet and the screw together with the rotation. She wondered: “Maybe it’s because of a magnet.” So she took it over and connected the battery, the screw, and the magnet directly