Chapter 6 — Electromagnetic Induction

Electromagnetic induction is the phenomenon in which a changing magnetic field induces an electric current in a closed coil, discovered around 1830 by Michael Faraday in England and Joseph Henry in the USA, and described by Faraday's law: ε = −N(dΦB/dt).

Class 12 Physics Chapter 6 covers electromagnetic induction — the generation of electric current by changing magnetic fields. Faraday and Henry's experiments showed that relative motion between a magnet and a coil, or a changing current in a nearby coil, induces an emf. Faraday's law states the induced emf equals the rate of change of magnetic flux: ε = −N(dΦB/dt). Lenz's law gives the direction: the induced current opposes the flux change that caused it. The chapter also explains motional emf (ε = Blv), self-inductance, mutual inductance, energy stored in inductors (W = ½LI²), and the working of an AC generator (ε = NBAω sin ωt).

1. 01Electromagnetic induction: electric current is induced in a coil whenever the magnetic flux through it changes with time (Faraday, Henry, ~1830).
2. 02Faraday's law: induced emf ε = −N(dΦB/dt); for a single-turn circuit, ε = −dΦB/dt, where magnetic flux ΦB = BA cos θ (SI unit: weber, Wb).
3. 03Lenz's law: the induced current flows in a direction that opposes the change in magnetic flux producing it, consistent with conservation of energy.
4. 04Motional emf: a conductor of length l moving with velocity v perpendicular to a uniform field B develops emf ε = Blv across its ends.
5. 05Self-inductance L of a solenoid: L = μr μ0 n² Al; self-induced emf ε = −L(dI/dt); energy stored W = ½LI²; mutual inductance M satisfies ε1 = −M(dI2/dt).
6. 06AC generator: a coil of N turns and area A rotating at angular frequency ω in field B produces alternating emf ε = NBAω sin ωt (peak value ε0 = NBAω).