How is electrical energy generated from changing magnetic fields?
Higher Level only — no Standard Level content in this topic
Faraday's discovery in 1831 was revolutionary: a changing magnetic flux induces an EMF. The rate of change matters — a stationary magnetic field, however strong, induces nothing. But move a conductor, change the field, or rotate a coil, and an EMF appears. This is how every generator on Earth works: mechanical energy (from a turbine driven by steam, water, or wind) is converted to electrical energy through electromagnetic induction.
Lenz's law tells you the direction of the induced EMF: it always opposes the change that caused it. This is not an arbitrary rule — it is required by conservation of energy. If the induced current reinforced the change instead of opposing it, you would have a self-accelerating system, which violates the first law of thermodynamics. Lenz's law is energy conservation in disguise.
A rectangular coil of 200 turns, area 0.04 m², rotates in a uniform magnetic field of 0.3 T at 50 Hz. Derive an expression for the induced EMF as a function of time, and find the peak EMF. Sketch one full cycle.
Faraday's Law of Electromagnetic Induction, Magnetic Flux & Induced EMF - Physics & ElectromagnetismLenz's Law, Right Hand Rule, Induced Current, Electromagnetic Induction - Physics
Michel van Biezen
Physics 45 Electromagnetic Induction: Faraday's Law and Lenz's Law (1 of 2) IntroductionPhysics 47.2 The Transformer (1 of 1) Example
WNY Tutor — worked problems
An emf of 24.0 mV is induced in a 500-turn coilThe primary coil of a transformer has N1 = 250 turns
Physics with Professor Matt Anderson — full course modules
Module 24 | Induction | Physics with Professor Matt AndersonModule 26 | AC Circuits | Physics with Professor Matt Anderson