Electromagnetic Induction
Definition
Making electricity from magnetism — moving a magnet near a wire (or a wire near a magnet) creates a voltage in the wire.
Symbol: · Unit: volt (V) — the induced EMF
Technical definition
The generation of an electromotive force in a conductor by a changing magnetic flux, ε = −dΦ/dt (Faraday's law). Lenz's law supplies the minus sign: the induced current always opposes the change that produced it.
Example
Shake a flashlight with a magnet sliding through a coil and the changing flux induces enough voltage to light the LED — no battery needed. Every power plant on Earth, from hydro dams to wind turbines, is just a giant version of this.
Induction needs change, not just a field. A magnet sitting motionless next to a coil induces exactly zero voltage — only a changing magnetic flux (moving magnet, changing current, rotating coil) does the job. Students who think 'magnet near wire equals electricity' cannot explain why transformers work on AC but are dead on DC.