Electromagnetic Induction

part 1

Faraday's Laws

• Experiments of Faraday and Henry
• Magnetic flux
• Faraday's law of electromagnetic induction
• Lenz's law and conservation of energy

part 2

Motional EMF and Eddy Currents

• Motional EMF
• Energy consideration in motional EMF
• Eddy currents and their applications
• Inductance concept

part 3

Self and Mutual Inductance

• Self-inductance and self-induced EMF
• Mutual inductance
• AC generator — principle and working

Faraday's law

$\varepsilon = -\frac{d\Phi}{dt}$; $\varepsilon = -N\frac{d\Phi}{dt}$

★ board favourite

Magnetic flux

$\Phi = \vec{B}\cdot\vec{A} = BA\cos\theta$

★ board favourite

Lenz's law

Induced current opposes change causing it

★ board favourite

Motional EMF

$\varepsilon = Bvl$

★ board favourite

Energy stored in inductor

$U = \frac{1}{2}LI^2$

★ board favourite

Self-inductance (flux linkage)

$N\Phi = LI$ → $\varepsilon = -L\frac{dI}{dt}$

★ frequently asked

Self-inductance of solenoid

$L = \mu_0 n^2 Al = \frac{\mu_0 N^2 A}{l}$

★ frequently asked

Mutual inductance

$\varepsilon_2 = -M\frac{dI_1}{dt}$

★ frequently asked

Peak EMF in AC generator

$\varepsilon = NBA\omega\sin\omega t = \varepsilon_0\sin\omega t$

★ frequently asked

Derive an expression for the motional EMF induced in a conducting rod of length l moving with velocity v perpendicular to a uniform magnetic field B. Show that this EMF is consistent with the work done by the external force.

What are eddy currents? State two useful applications and one method of minimising them.

State Faraday's laws of electromagnetic induction. A rectangular coil of area A and N turns is rotated in a uniform magnetic field B with angular frequency ω. Derive the expression for the EMF induced.

Define mutual inductance between two coplanar coils. Derive an expression for the mutual inductance of two long coaxial solenoids of the same length. On what factors does it depend?

A bar magnet is moved towards a circular coil. State the direction of induced current as seen from the magnet side when (a) the magnet approaches, (b) the magnet recedes.

State Lenz's law. Show that Lenz's law is a consequence of the conservation of energy. Explain with an example of a magnet approaching a coil.

Define self-inductance. Derive an expression for the self-inductance of a long solenoid. A coil of 100 turns and area 0.1m² is placed in a magnetic field changing at 2T/s. Find the induced EMF.

Define magnetic flux and write its SI unit. When is the flux linked with a coil maximum?

Derive the expression for the energy stored in an inductor of self-inductance L carrying a steady current I.

How many marks is Electromagnetic Induction worth in the Class 12 board exam?

Around 4 marks of the 70-mark CBSE Physics theory paper, based on the official unit-wise weightage. Lenz's law and self-inductance numerics score well.

Is Electromagnetic Induction easy or hard?

It's rated hard — one of the tougher chapters in Class 12 Physics. Most students need about 4 hours to cover it well.

What are the important topics in Electromagnetic Induction?

The chapter covers 10 NCERT topics in 3 areas: Faraday's Laws; Motional EMF and Eddy Currents; Self and Mutual Inductance.

What questions come from Electromagnetic Induction in board exams?

Between 2018–2024, CBSE board papers asked questions from this chapter on Motional EMF, Eddy Currents, Faraday's Law, Mutual Inductance — 1- to 5-mark questions.