⚡ CBSE · Class 12 · Physics · Chapter 6

Electromagnetic
Induction

Complete chapter resources for CBSE Class 12 Physics — Faraday's laws, Lenz's law, motional EMF, self and mutual inductance, sample questions, previous year board questions, and instant AI question paper generation.

4Topics
6–8Board marks
8Sample questions
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Key Formulas — Chapter 6
  • Magnetic flux: Φ = B · A · cos θ
  • Faraday's law: EMF = −N · dΦ/dt
  • Motional EMF: EMF = Blv
  • Self-inductance: EMF = −L · dI/dt
  • Mutual inductance: EMF₂ = −M · dI₁/dt
  • Energy in inductor: U = ½LI²
Chapter Overview

What this chapter covers

Electromagnetic Induction is the phenomenon by which a changing magnetic flux through a circuit induces an electromotive force (EMF) in that circuit. Faraday's first law states that an EMF is induced whenever the magnetic flux linked with a conductor changes; his second law quantifies this as EMF = −N(dΦ/dt), where N is the number of turns and the negative sign encapsulates Lenz's law — the induced current always opposes the change that caused it, a direct consequence of energy conservation.

The chapter develops two important engineering applications. Motional EMF (EMF = Blv) arises when a conductor of length l moves with velocity v perpendicular to a uniform magnetic field B; free electrons experience a Lorentz force that acts as the source of EMF. The concept of inductance — both self-inductance L of a single coil and mutual inductance M between two coupled coils — is then introduced to characterise how strongly a circuit resists changes in current. The energy stored in an inductor is U = ½LI².

Board questions consistently test Faraday's and Lenz's law in the context of a moving bar on conducting rails, solenoid-based inductance calculations, and energy-storage problems. The chapter also connects directly to Chapter 7 (Alternating Current), making a thorough understanding here essential for the full electromagnetism arc of the Class 12 syllabus.

Topics

What's inside Chapter 6

As per NCERT Class 12 Physics Part I (CBSE syllabus)

Topic 1
Magnetic Flux & Faraday's Laws
Definition of magnetic flux Φ = BA cos θ. Faraday's first and second laws of electromagnetic induction. The role of the rate of change of flux in determining the magnitude of induced EMF.
Topic 2
Lenz's Law & Conservation of Energy
Direction of induced current via Lenz's law. Fleming's right-hand rule. Physical interpretation: induced effects always oppose the cause — the induction analogue of Newton's third law and energy conservation.
Topic 3
Motional EMF & Eddy Currents
EMF = Blv for a conductor moving in a magnetic field. Energy analysis of the rod-on-rails setup. Eddy currents — their origin, heating effect, and engineering applications (magnetic braking, induction heating).
Topic 4
Inductance — Self & Mutual
Self-inductance L: back-EMF = −L(dI/dt). Mutual inductance M between two coils. Inductance of a solenoid and toroid. Energy stored: U = ½LI². Coefficient of coupling for paired coils.
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Ch 4 · Moving Charges & Magnetism
Magnetic field of a solenoid, Biot-Savart law, Lorentz force
Ch 1–3 · Electrostatics & Current
Electric potential, current, resistance — forms the circuit context for induced EMF
Chapter 6 Electromagnetic
Induction
Leads to
Ch 7 · Alternating Current
AC generators, transformers, LC circuits — all built directly on inductance
Ch 8 · Electromagnetic Waves
Maxwell's displacement current completes the induction ↔ radiation link
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 12 Physics board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Assertion-Reason 1 1–2 Direction of induced current, Lenz's law statement, or flux calculation
Very Short Answer 2 1 State Faraday's second law or define self-inductance with SI unit
Short Answer 3 1 Motional EMF derivation or mutual inductance of two coaxial solenoids
Long Answer / Derivation 5 0–1 Rod-on-rails energy analysis, inductance of solenoid, or combined Faraday + Lenz problem
Total (approximate) 6–8 3–5 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 12 Physics Chapter 6. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
A bar magnet is moved towards a closed conducting loop. According to Lenz's law, the induced current in the loop will: (a) Attract the magnet (b) Repel the magnet (c) Have no effect on the magnet (d) Reverse direction when the magnet stops
Q2 Easy 2 marks Short Answer
Define self-inductance of a coil. Write its SI unit and give the dimensional formula of inductance.
Q3 Medium 2 marks Short Answer
A rectangular coil of area 0.04 m² and 200 turns is placed with its plane perpendicular to a magnetic field of 0.5 T. The field is reduced to zero in 0.1 s. Calculate the magnitude of the induced EMF.
Q4 Medium 3 marks Short Answer
A conducting rod of length 0.5 m moves with a velocity of 4 m/s perpendicular to a uniform magnetic field of 0.8 T. (i) Find the motional EMF induced in the rod. (ii) If the rod forms part of a circuit of total resistance 2 Ω, find the induced current.
Q5 Medium 3 marks Short Answer
Derive an expression for the self-inductance of a long solenoid of length l, cross-sectional area A, and n turns per unit length. What happens to the inductance if the number of turns is doubled while the length is kept constant?
Q6 Hard 4 marks Derivation + Problem
A conducting rod PQ of mass m and resistance R can slide without friction on two parallel horizontal rails separated by a distance l. The rails are connected at one end and placed in a uniform vertical magnetic field B. (i) Show that when the rod moves with velocity v, the induced EMF is Blv. (ii) Derive an expression for the force required to maintain the rod at constant velocity. (iii) Calculate the power delivered by this force and show it equals the rate of Joule heating.
Q7 Hard 5 marks Long Answer
Two coaxial solenoids of length l have n₁ and n₂ turns per unit length and cross-sectional area A₁ (inner) and A₂ (outer), with A₁ < A₂. (i) Derive an expression for their mutual inductance M. (ii) If n₁ = 1000 turns/m, n₂ = 2000 turns/m, A₁ = 4 × 10⁻⁴ m², and l = 0.2 m, calculate M. (iii) If the current in the outer solenoid changes at 5 A/s, find the induced EMF in the inner solenoid.
Q8 Hard 5 marks Case-Based
An inductor of self-inductance L = 200 mH carries a steady current of 5 A. (i) Calculate the energy stored in the magnetic field of the inductor. (ii) If the current is reduced to zero in 0.01 s, find the average back-EMF induced. (iii) Explain, with reference to Lenz's law, why the back-EMF opposes the decrease in current. (iv) State one practical application of this property of inductors.
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 12 Physics board papers — Electromagnetic Induction chapter.

Board 20223 marks
A straight conductor of length 0.4 m is moved with a speed of 7 m/s perpendicular to a magnetic field of intensity 0.9 T. Calculate the EMF induced in the conductor. If the conductor is connected in a circuit of resistance 0.2 Ω, find the current flowing through it and the power dissipated. (CBSE All India 2022)
Board 20232 marks
State Faraday's law of electromagnetic induction. A coil of N turns and area A is rotated at a uniform angular velocity ω in a uniform magnetic field B. Write the expression for the instantaneous EMF induced in the coil. (CBSE Delhi 2023)
Board 20205 marks
(a) Define mutual inductance and write its SI unit. (b) Derive an expression for the mutual inductance of two long coaxial solenoids of the same length l, having n₁ and n₂ turns per unit length and radii r₁ and r₂ respectively (r₁ < r₂). (c) State the factors on which the mutual inductance of a pair of coils depends. (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Electromagnetic Induction carry in the CBSE Class 12 Physics board exam? +
Electromagnetic Induction typically carries 6–8 marks in the CBSE Class 12 Physics board exam. Questions appear as one 1-mark MCQ or assertion-reason, one 2-mark short answer on Faraday's or Lenz's law, and one 3–5 mark problem on self-inductance, mutual inductance, or motional EMF. The chapter has featured in every CBSE Class 12 Physics board paper for the last decade.
What is the difference between self-inductance and mutual inductance? +
Self-inductance (L) is the property of a single coil by which a change in its own current induces an EMF in itself: EMF = −L (dI/dt). Mutual inductance (M) is the property of two coupled coils where a changing current in one coil induces an EMF in the other: EMF₂ = −M (dI₁/dt). CBSE board problems often ask students to calculate M for two coaxial solenoids or L for a toroid, and both concepts can appear in a single 5-mark question.
How do I apply Lenz's law in board exam problems? +
Lenz's law states that the direction of the induced EMF (and hence induced current) is always such that it opposes the change in magnetic flux that caused it — this is a consequence of energy conservation. In board problems, first identify whether flux is increasing or decreasing, then determine the direction of the induced current so that its magnetic field opposes the change. Common board question types include a bar magnet approaching a coil and a conducting rod moving on parallel rails.
What is motional EMF and how is its formula derived? +
Motional EMF is the EMF induced in a conductor moving with velocity v in a magnetic field B. For a rod of length l moving perpendicular to B, the EMF = Blv. This is derived by noting that free charges in the moving conductor experience a Lorentz force (F = qvB), which separates positive and negative charges to the ends of the rod, creating a potential difference. CBSE boards frequently ask a 3-mark derivation of this expression.
How do I generate a custom question paper for Electromagnetic Induction using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 12 Physics, select Chapter 6 (Electromagnetic Induction), set your preferred question-type mix (MCQ, short answer, derivation, numerical) and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.