Faraday's Law
Definition
The rule that a changing magnetic field creates electricity — the principle behind every generator and transformer.
Unit: V (EMF)
Technical definition
The induced electromotive force around a closed loop equals the negative rate of change of magnetic flux through it: ε = −N·dΦ/dt. One of Maxwell's equations; the negative sign (Lenz's law) enforces energy conservation.
Example
Spinning a coil at 60 revolutions per second in a magnetic field makes the flux oscillate — inducing the 60 Hz alternating voltage of the power grid.
Common confusion
It is the CHANGE in flux that matters, not the flux itself. A huge steady magnetic field induces nothing; a tiny field flipping rapidly can induce a large voltage. Students often forget the time derivative.