🙅 楞次定律：感应电流“不乐意”变化🙅 Lenz's Law: The Current That Resists Change
上一片说：变化越快，电越强。可感应电流到底往哪边流、磁铁又会受到什么力？这一片的楞次定律回答：电流不乐意被你改变。Last leaf: the faster the change, the stronger the current. But which way does the current flow, and what force does the magnet feel? Lenz's law answers: the current is not happy about being changed.
第 1 步：一张拒绝的手掌Step 1: A refusing palm
磁铁兴冲冲地靠近线圈，线圈会热情接纳吗？The magnet rushes toward the coil — will the coil welcome it?
不会。线圈不乐意磁通量被“塞”进来，立刻建立自己的磁场，正面迎着磁铁——像伸出一只手掌，把它往外推。所以磁铁靠近时，感受到的是排斥力：来？拒！No. The coil refuses the incoming flux, builds its own field facing the magnet, and sticks out a palm to push it back. So a magnet moving in feels a repelling force: coming? refused!
那磁铁掉头要走，线圈总该松口气了吧？And when the magnet turns to leave — the coil can relax now, right?
第 2 步：来拒去留Step 2: Come? Push away. Go? Pull back.
更不行。磁通量要走，比来更让它难受，它马上变得“舍不得”，用力把磁铁往回拉。靠近就推开、离开就拉回，四个字：来拒去留。感应电流的方向，永远朝着“反抗变化”的那一边。Quite the opposite. Flux leaving upsets it even more, so it holds on and pulls the magnet back. Push when it comes, pull when it goes: four words — oppose the change. The induced current always flows the way that fights the change.
它的“脾气”在实验室里，能闹出多大动静？How loud can this temper get in a lab?
第 3 步：会跳的铝环Step 3: The jumping ring
把铁芯线圈通上交流电，上面套一个闭合铝环——变化的磁场让铝环感应出电流，而铝环的电流拼命抗拒，结果“拒绝”的力量把它直接弹上天！换成有缺口的开口环：电流绕不完整圈，它就乖乖待在原地。Put a closed aluminum ring over an AC iron-core coil: the changing field induces a current, and that current pushes back so hard the ring is launched into the air! Swap in a split ring with a slit: the current can't complete a loop, and it just sits there.
🎮 你来当小小实验员（1 分钟）🎮 Your turn: the little lab assistant (1 minute)
按提示操作磁铁——靠近、远离、或者停住不动，观察线圈的反应，再判断它使的力、还有电流的方向。4 关等着你。Move the magnet as the mission asks — approach, leave, or hold still — watch the coil's reaction, then judge its force and the current's direction. 4 missions await.
一句话记住它：感应电流总“反抗”引起它的变化——来拒去留，它是能量守恒派来的小卫士。Remember it in one line: an induced current always opposes the change that made it — push away, pull back; energy conservation's little guardian.
磁铁靠近就推开（排斥），离开就拉回（吸引）——来拒去留Coming? Pushed away. Going? Pulled back.感应电流的磁场，总跟磁铁磁场的变化对着干The induced field always fights the change in flux没有变化就没有电流；跳跃环：闭合环被弹飞，开口环不动No change, no current; jumping ring: the closed ring flies, the split ring stays
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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