CBSE Class 12 Physics: Electromagnetic Induction — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: State Faraday's laws of electromagnetic induction.
  Ans: First Law: Whenever the magnetic flux linked with a coil changes, an EMF is induced in the coil. The induced EMF lasts as long as the change in flux continues. Second Law: The magnitude of induced EMF is directly proportional to the rate of change of magnetic flux. e = -dφ/dt (negative sign from Lenz's law). For N turns: e = -N(dφ/dt).
• Q: State and explain Lenz's Law. Show it is consistent with conservation of energy.
  Ans: Lenz's Law: The direction of induced current is such that it opposes the change in magnetic flux that causes it. Conservation of energy: If the induced current aided the change (instead of opposing), it would increase the flux, inducing more current, creating more flux — perpetual energy generation from nothing. This violates conservation of energy. Therefore, the induced current must oppose the change.
• Q: Derive the expression for motional EMF.
  Ans: A conducting rod PQ of length l moves with velocity v perpendicular to a uniform magnetic field B. A free electron in the rod experiences force F = qvB (Lorentz force). This drives electrons from P to Q, creating potential difference. Work done on charge q: W = qvBl. EMF = W/q = Bvl. Using Faraday's law: Area swept per second = lv. dφ/dt = Blv. e = Blv.
• Q: Define self-inductance. Derive the expression for self-inductance of a solenoid.
  Ans: Self-inductance (L) is the property of a coil to oppose any change in current through it by inducing an EMF. e = -L(dI/dt). For a solenoid: N turns, length l, area A, current I. B = μ₀nI = μ₀NI/l. Flux φ = BA = μ₀NIA/l. Total flux linkage = Nφ = μ₀N²IA/l. L = Nφ/I = μ₀N²A/l. Unit: Henry (H).

Long Answer / Application Questions (4-6 Marks)

• Q: Explain the working of an AC generator with diagram.
  Ans: Principle: Electromagnetic induction. Construction: Armature coil ABCD rotates between poles of strong magnet. Slip rings and carbon brushes for external circuit connection. Working: As coil rotates, magnetic flux changes continuously. By Faraday's law, EMF is induced: e = NBA ω sin(ωt) = e₀ sin(ωt). Maximum EMF e₀ = NBAω. Output is alternating (sinusoidal). Frequency = ω/(2π).

Exam Tips for This Chapter

• Revise all definitions and laws from Electromagnetic Induction — commonly asked as 1-2 mark questions
• Practice diagrams related to Electromagnetic Induction — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Electromagnetic Induction carries significant marks in the board exam