Faraday's Discovery: Electricity from Magnetism
In 1831, Michael Faraday made one of the most important discoveries in physics: a changing magnetic field induces an electric current. By moving a magnet through a coil of wire, he generated electricity without any battery. This principle — electromagnetic induction — is the foundation of virtually all electrical power generation in the world today.
The Law of Induction
Faraday's law is elegantly simple: the induced EMF equals the negative rate of change of magnetic flux. For a rotating coil in a uniform field, the flux varies as Φ = BAcos(ωt), and the induced EMF is ε = NBAω sin(ωt). The EMF is maximum when the flux is changing fastest (coil perpendicular to field) and zero when the flux is at its peak (coil parallel to field).
Lenz's Law and Energy Conservation
The negative sign in Faraday's law reflects Lenz's law: the induced current always opposes the change that produced it. If the flux is increasing, the induced current creates a field that resists the increase. This opposition is not merely a mathematical sign — it requires mechanical work to maintain the changing flux, which is how generators convert mechanical to electrical energy.
From Faraday to the Power Grid
Every power plant in the world — whether coal, nuclear, hydro, wind, or gas — generates electricity using Faraday's law. Turbines spin coils in magnetic fields (or magnets past coils), producing alternating current at 50 or 60 Hz. The voltage is then stepped up by transformers (also based on induction) for efficient long-distance transmission.