Chapter 6 — Electromagnetic Induction

Chapter 6 of the Class 12 Physics NCERT textbook, "Electromagnetic Induction", covers the phenomenon in which a changing magnetic field induces an electric current in a closed coil, discovered around 1830 by Michael Faraday and Joseph Henry, and described by Faraday's law: ε = −N(dΦB/dt).

• Generating current from change — The chapter reverses earlier ideas: instead of current making magnetism, a changing magnetic flux creates current. Faraday and Henry's experiments revealed that motion or a changing field induces an EMF.
• Faraday's and Lenz's laws — Faraday's law quantifies the induced EMF as the rate of change of flux, while Lenz's law fixes its direction — the induced current always opposes the change, in line with energy conservation.
• Inductance and stored energy — Self- and mutual inductance describe how circuits oppose changes in their own and each other's currents, with energy stored in an inductor's magnetic field.
• From principle to generator — These ideas culminate in the AC generator, where a rotating coil in a magnetic field turns mechanical motion into an alternating EMF — the basis of practical power generation.

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).