Table of Contents
Faraday's Law
Faraday's law states that a changing magnetic flux through a circuit induces an electromotive force (EMF). The magnitude equals the rate of flux change multiplied by the number of turns. Discovered by Michael Faraday in 1831, this principle underlies electric generators, transformers, induction motors, and wireless charging.
The negative sign (Lenz's law) indicates the induced EMF opposes the change that produced it, a consequence of energy conservation. Together with Ampere's law, Faraday's law forms the foundation of classical electromagnetism unified by Maxwell's equations.
Formula
Applications
| Application | Principle |
|---|---|
| Generators | Rotating coil in B field |
| Transformers | AC in primary induces EMF in secondary |
| Induction cooking | Eddy currents heat cookware |
| Metal detectors | Eddy currents alter coil inductance |
| Wireless charging | Oscillating field induces receiver current |
FAQ
What is Lenz's law?
The induced current opposes the flux change that created it. If flux increases, induced current creates opposing field. This conserves energy - the induced current requires mechanical work to maintain the flux change, which is how generators convert mechanical to electrical energy.
How do generators work?
A coil rotates in a magnetic field, continuously changing the flux through it. This induces alternating EMF at the rotation frequency. Larger coils, stronger magnets, more turns, and faster rotation all increase output voltage.
What is magnetic flux?
Flux = B*A*cos(theta), measured in webers (Wb). One Wb = 1 T*m^2. Changes in B, A, or angle all induce EMF. This is why both rotating (generators) and stationary (transformers) configurations work.