What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

State Faraday's law of induction.

The induced emf equals the negative rate of change of magnetic flux, \(\varepsilon=-d\Phi/dt\).

State Lenz's law and its significance.

The induced current opposes the change causing it; it expresses conservation of energy.

What is motional emf?

The emf \(\varepsilon=Blv\) induced in a rod of length \(l\) moving with speed \(v\) perpendicular to \(B\).

Define self-inductance.

The flux linkage per unit current in a coil, \(L=\Phi/I\); it opposes current changes.

What energy is stored in an inductor?

\(U=\tfrac{1}{2}LI^2\), held in the magnetic field of the coil.

Define mutual inductance.

The flux linkage in one coil per unit current in a neighbouring coil, \(M=\Phi_2/I_1\).

What are eddy currents and one use?

Induced currents in bulk conductors; used in electromagnetic braking and induction furnaces.

Why are transformer cores laminated?

To increase resistance to eddy currents, reducing energy loss as heat.

How does an AC generator produce emf?

By rotating a coil in a magnetic field, changing flux to give \(\varepsilon=\varepsilon_0\sin\omega t\).

On what factors does induced emf in a rotating coil depend?

Number of turns, area, field strength and angular speed: \(\varepsilon_0=NBA\omega\).

Electromagnetic Induction

Class 12 Physics · Physics Part I · Chapter 6

163 members in the CBSE community

View all

CBSE Class 12 · Physics

Capacitance: 32 marks in 4 papers, most asked

Marks booster + cheatsheet: key concepts in 2 lines each
34 marks in 4 papers: Magnetism, Ch 4–5
33 marks in 4 papers: Induction and AC
26 marks in 4 papers: Current Electricity
Every formula with its page number
What each 2025 board paper asked

Page 1 free about 8 min read, Full kit about 55 min read

₹159See the full kit

CBSE Class 12 · PhysicsTrending

Ray Optics: 35 marks across four papers

Marks booster + cheatsheet: key concepts in 2 lines each, common traps
22 marks across four papers: Wave Optics
22 marks: Dual Nature, with 4-mark cases
Common traps that cost marks, listed
13 marks each: Atoms and Nuclei
7 marks in all four papers: Semiconductors

Page 1 free about 8 min read, Full kit about 55 min read

₹159See the full kit

View all 46 amazing Marks Booster kits →

Summary

A changing magnetic flux through a circuit induces an emf—the heart of electromagnetic induction. Magnetic flux is \(\Phi=\vec{B}\cdot\vec{A}=BA\cos\theta\). Faraday's law states that the induced emf equals the rate of change of flux, \(\varepsilon=-\dfrac{d\Phi}{dt}\), while Lenz's law, expressed by the negative sign, ensures the induced current opposes the change producing it—a statement of energy conservation. A conductor of length \(l\) moving with speed \(v\) across a field generates a motional emf \(\varepsilon=Blv\). Changing fluxes also drive eddy currents in bulk conductors, used in braking and induction heating but minimised by lamination in transformers. Self-inductance \(L\) opposes changes in a coil's own current, with emf \(\varepsilon=-L\dfrac{dI}{dt}\) and stored energy \(U=\tfrac{1}{2}LI^2\). Mutual inductance \(M\) couples two coils, the basis of the transformer. An AC generator converts mechanical energy into electrical energy by rotating a coil in a field, producing a sinusoidal emf \(\varepsilon=\varepsilon_0\sin\omega t\), embodying the link between motion, magnetism and electricity.

Magnetic flux and Faraday's lawLenz's law and energy conservationMotional emfEddy currents and applicationsSelf and mutual inductanceAC generator

Key terms

Magnetic flux

Field threading a surface, \(\Phi=BA\cos\theta\); SI unit weber.

Faraday's law

Induced emf equals the negative rate of change of flux, \(\varepsilon=-d\Phi/dt\).

Lenz's law

Induced current opposes the change in flux, conserving energy.

Motional emf

Emf \(\varepsilon=Blv\) in a conductor moving across a field.

Self-inductance

Property opposing change in a coil's own current, emf \(=-L\,dI/dt\).

Eddy currents

Induced circulating currents in bulk conductors, reduced by lamination.

Extra questions & answers

Try one from this chapter

Faraday's law states the induced emf equals:

Flashcards & interactive practice