Physics XII - Chapter 6: Electromagnetic Induction
Master Electromagnetic Induction Class 12 MCQs. Practice Faraday's law, Lenz's law, induced emf, self & mutual inductance with important exam questions.
Quick Revision
- Faraday's Law: ε = -dΦ_B/dt; induced emf proportional to rate of change of magnetic flux.
- Magnetic Flux: Φ_B = B·A = BA cosθ; number of magnetic field lines through area.
- Lenz's Law: Induced current opposes the change producing it; minus sign in Faraday's law.
- Motional EMF: ε = Blv; induced when conductor moves perpendicular to magnetic field.
- Motional EMF in Rotating Rod: ε = ½Bωl²; rod rotating about one end in magnetic field.
- Self Induction: ε = -L(dI/dt); emf induced in coil due to its own current change.
- Self Inductance (L): L = Φ/I; flux linkage per unit current with SI unit henry (H).
- Inductance of Solenoid: L = μ₀n²Al; depends on geometry and core material.
- Energy Stored in Inductor: U = ½LI²; magnetic potential energy in inductor.
- Mutual Induction: ε₂ = -M(dI₁/dt); emf in coil 2 due to current change in coil 1.
- Mutual Inductance (M): M = Φ₂/I₁ = Φ₁/I₂; same for both coils with SI unit henry (H).
- AC Generator: Converts mechanical to electrical energy; ε = NBAω sinωt.
- Eddy Currents: Circular induced currents in bulk metals; cause heating and damping.
- Transformer: V_s/V_p = N_s/N_p = I_p/I_s; changes AC voltage levels.
- Back EMF: Induced emf in motors opposing applied voltage; regulates current draw.
- Induction Stove: Uses eddy currents for heating without direct contact.
- Magnetic Braking: Uses eddy currents for smooth, contactless braking.
- Flux Conservation: Magnetic flux through superconducting loop remains constant.
- Induced Electric Field: Changing magnetic field produces non-conservative electric field.
Basic Level Questions
Chapter Summary
Electromagnetic Induction reveals one of nature's most elegant symmetries - just as electric currents create magnetic fields, changing magnetic fields can create electric currents. This beautiful reciprocity, discovered by Michael Faraday, forms the foundation of our modern electrical world. The chapter begins with Faraday's groundbreaking experiments that showed how relative motion between a conductor and magnetic field can generate electricity.
We explore how magnetic flux - the number of field lines passing through a surface - becomes the key quantity that drives electromagnetic induction. Lenz's law adds a touch of nature's wisdom to the process, ensuring that induced currents always oppose the changes that create them, embodying the principle of conservation of energy in electromagnetic phenomena.
The concepts of self-inductance and mutual inductance show us how coils can store magnetic energy and how transformers can magically step voltages up or down. From the gentle hum of transformers to the dramatic spark when circuits break, electromagnetic induction manifests in countless ways around us. Practical applications abound - AC generators that power our cities, induction cooktops that heat without flames, and magnetic brakes that stop high-speed trains smoothly.
This chapter truly bridges the gap between abstract field theory and the electrical technologies that define modern civilization, showing how the dance between electricity and magnetism literally keeps our lights on and our world moving forward.