Lenz’s Law
Core Sentence / 核心句
The induced current creates a magnetic field that opposes the change in magnetic flux.
中文理解：感应效应反抗的是磁通量的变化，不是永远反向于原 magnetic field。
Direction Logic / 方向逻辑
- flux increasing：induced opposes the original flux direction；
- flux decreasing：induced supports the original flux direction to resist the decrease。
Stable Procedure / 固定步骤
- choose a viewing direction / surface normal；
- identify external flux direction；
- decide increasing or decreasing；
- choose induced to oppose that change；
- use right-hand grip rule to obtain current direction。
Why It Must Oppose / 为什么必须反抗
如果 induced effect 增强导致它自身的变化，系统会无外界做功地自发放大 current 与 energy，违反 energy conservation。Lenz direction ensures mechanical or source work supplies the induced electrical energy。
Deep Phrase / 记忆句
Faraday gives the amount; Lenz gives the direction.
法拉第定大小，楞次定方向。
Watch Out / 易错点
- oppose the flux change, not simply the field；
- current direction comes only after induced-field direction；
- entering and leaving a field give opposite currents；
- a loop moving entirely inside a uniform field may have no net EMF because flux is unchanged。
Search and Source Mentions / 搜索与出现位置
Mentioned In / 出现位置
Connected Notes / 连接
- Faraday’s Law
- Magnetic Flux
- Electromagnetic Induction
- Electromagnetic Damping
- Inductors
- energy conservation