Definition
A principle of electromagnetism stating that an induced electric current always flows in the direction that opposes the change in magnetic field that produced it. In other words, when a magnetic field around a conductor changes, the resulting induced current creates its own magnetic field that pushes back against the original change.
Plain English
When a changing magnet causes electricity to flow in a wire, that electricity always pushes back against whatever caused it. Nature resists the change.
Context Anchor
Seen when studying aircraft electrical systems, especially generators, alternators, magnetos, and electrical coils.
Derivation
Named after Heinrich Lenz, the Russian physicist who described the effect in 1834. The 'law' part is just the scientific use of the word, meaning a consistent rule that nature follows.
Why Pilots Care
Explains why engine power is required to turn an alternator or generator and why output cannot be increased without additional mechanical load.
Analogy
Imagine pushing a magnet into a coil of wire. The coil 'pushes back' against your hand as the current flows. The harder you push, the harder it resists. Nothing in the system is alive, but it behaves as if it doesn't want to be disturbed.
Grounding Statement
If a magnet moves toward a coil of wire, the current created in the coil acts in a way that resists that motion.
Intuition Check
Do not think the induced current helps the original change. In Lenz's law, the induced current opposes the change that produced it.
Example Sentence 1
The drag the pilot feels when the alternator picks up a heavy electrical load is a direct result of Lenz's Law.
Example Sentence 2
Lenz's Law ensures the current induced in the generator armature opposes rotation, preventing free electrical output.