Class 12 Physics Chapter 6 Electromagnetic Induction – Revision Notes

A changing magnetic flux is the heart of electromagnetic induction, and this Class 12 Physics Chapter 6 summary traces that idea through Faraday’s and Lenz’s laws, motional emf, AC generators, and self- and mutual inductance.

Last Updated: September 10, 2026

Magnetic Flux and Faraday’s Law

• Magnetic flux through a surface: Φ=B·A=BA cosθ.
• Faraday’s law: induced emf E=−N(dΦ/dt).

Lenz’s Law

• The induced emf/current always opposes the change in flux that produces it — a direct consequence of energy conservation.

Motional EMF

• For a rod of length l moving with velocity v perpendicular to field B: E=Blv.
• For a rod rotating about one end with angular frequency ω: E=½Bωl².

AC Generator

• A coil of N turns, area A, rotating at angular speed ω in field B produces emf E=E₀sin(ωt), where E₀=NBAω is the peak emf.
• The average emf (and average current) over a full cycle is zero, since the emf is purely sinusoidal.

Self- and Mutual Inductance

• Self-inductance: E=−L(dI/dt); SI unit is the henry (H).
• Mutual inductance: E=−M(dI/dt); relates the emf in one coil to the changing current in a neighbouring coil.

Eddy Currents

• Currents induced within the bulk of a conductor (not just along a wire) due to a changing flux; used constructively in induction furnaces and electromagnetic braking, and minimised (via lamination) in transformer cores to reduce energy loss.

One-Line Summary

A changing magnetic flux induces an emf (Faraday’s law) in a direction that always opposes the change producing it (Lenz’s law), underlying motional emf, AC generators, and self- and mutual inductance.