Electromagnetic Induction Class 12 Physics Notes 2026–27

Chapter 6 — complete CBSE-focused notes on electromagnetic induction, magnetic flux, Faraday's laws, induced EMF and current, Lenz's law, self-induction and mutual induction.

Class 12 Physics Chapter 6 CBSE 2026–27 Concepts + Numericals

Scope first: Electromagnetic Induction is Chapter 6 of Unit IV, Electromagnetic Induction and Alternating Currents. The official CBSE 2026–27 curriculum assigns 18 marks to Unit IV for Chapters 6 and 7 together; CBSE does not prescribe a separate fixed mark allocation for Chapter 6. The current Chapter 6 syllabus names electromagnetic induction, Faraday's laws, induced EMF and current, Lenz's law, self-induction and mutual induction. AC generator and transformer are listed under Chapter 7, Alternating Current, not Chapter 6.

Official CBSE Physics Curriculum 2026–27 · Official Class XII 2026–27 SQP & Marking Scheme

Important syllabus correction: Many online “Electromagnetic Induction Class 12” pages include the AC generator in Chapter 6 because it appears at the end of the NCERT chapter sequence. For CBSE 2026–27 syllabus mapping, however, AC generator is explicitly listed under Chapter 7: Alternating Current. This page therefore keeps AC-generator derivation and transformer content out of the Chapter 6 core.

1. What You Will Learn in Chapter 6

Electromagnetic induction explains how a changing magnetic environment can produce an induced EMF in a conductor or circuit. The central idea is simple: when the magnetic flux linked with a circuit changes, an EMF can be induced.

Magnetic flux → change
Learn what magnetic flux means and how changing field, area or orientation changes the flux linked with a circuit.

Change → induced EMF
Faraday's law connects the rate of change of magnetic flux with the magnitude of induced EMF.

EMF → direction
Lenz's law determines the direction of the induced effect by opposing the change in flux that produces it.

Current → induction
A closed conducting path allows the induced EMF to drive an induced current.

One coil → self-induction
A changing current in a coil can induce an EMF in the same coil.

Two coils → mutual induction
A changing current in one coil can induce an EMF in a nearby second coil.

2. The Big Idea: What Is Electromagnetic Induction?

Electromagnetic induction is the phenomenon in which an EMF is induced in a circuit when the magnetic flux linked with the circuit changes.

This definition is more precise than saying simply “a moving magnet produces electricity.” Motion is only one way to change magnetic flux. Flux can also change because the magnetic field changes, the area of the circuit changes, or the orientation of the circuit changes.

One-line memory rule: No change in magnetic flux → no induced EMF from electromagnetic induction. A magnetic field can be very large and still produce no induced EMF if the linked flux remains constant.

3. Faraday and Henry — The Experimental Foundation

The phenomenon was established through experiments involving magnets, coils and changing currents. The experiments show that the crucial factor is not simply the presence of a magnetic field, but a change in magnetic flux linkage.

Situation	Observation	What it teaches
Magnet moved toward a coil	Galvanometer deflects while the magnet moves.	A changing magnetic environment can induce EMF.
Magnet moved away from the coil	Deflection reverses.	Changing the flux in the opposite sense reverses the induced effect.
Magnet held stationary near the coil	No sustained deflection.	A constant flux does not produce a sustained induced EMF.
Second coil moved near/away from a first coil	Momentary deflection occurs during the change.	Relative motion is another way to change flux linkage.
Current in a nearby coil switched on/off	Momentary induced effect appears in the other coil.	Motion is not essential; changing current can change magnetic flux and induce EMF.

Exam trap: “A magnetic field induces current” is incomplete. The better statement is: a change in magnetic flux linked with a circuit induces an EMF; an induced current flows when the conducting path is closed.

4. Magnetic Flux

Magnetic flux measures the magnetic field passing through a given surface. For a uniform magnetic field and a plane surface:

Magnetic flux: Φ_B = B A cos θ

Here B is the magnetic-field magnitude, A is the area of the surface, and θ is the angle between the magnetic field B and the area vector (normal to the surface).

θ = 0°: B is along the area vector → Φ_B = BA, maximum positive flux.

θ = 90°: B is perpendicular to the area vector → Φ_B = 0.

Flux and the plane of the coil — the common confusion

If a question gives the angle between B and the plane of the coil, that angle is not the same θ used directly in BA cos θ. The area vector is perpendicular to the plane.

Fast check: If magnetic field lines are perpendicular to the plane of the coil, they are parallel to the area vector, so θ = 0° and the flux magnitude is maximum: Φ_B = BA.

SI unit of magnetic flux

The SI unit of magnetic flux is the weber (Wb).

1 Wb = 1 T m² = 1 V s

5. What Can Change Magnetic Flux?

From Φ_B = BA cos θ, the linked flux can change if any of the relevant quantities changes.

Change B
The magnetic-field magnitude changes with time.

Change A
The area of the loop changes, such as when a conducting rod slides along rails.

Change θ
The orientation of the loop changes relative to the field.

Move the circuit
Relative motion between a conductor/circuit and a magnetic field can change the flux linkage.

This gives a powerful problem-solving method:

Before using a formula, ask: What exactly is changing — B, A, θ, or more than one of them?

6. Faraday's Laws of Electromagnetic Induction

First law

Whenever the magnetic flux linked with a circuit changes, an EMF is induced in the circuit.

Second law

The magnitude of the induced EMF is proportional to the rate of change of magnetic flux linkage.

ε = − dΦ_B/dt (single turn)

ε = − N dΦ_B/dt (N-turn coil)

For a finite change over a time interval, the average induced EMF is:

ε_avg = − N ΔΦ_B/Δt

What does the minus sign mean? The minus sign represents Lenz's law. It gives the direction of the induced EMF relative to the change in flux; it is not a statement that EMF itself is always negative.

7. Lenz's Law

Lenz's law: The induced current flows in such a direction that the magnetic effect produced by it opposes the change in magnetic flux that caused the induction.

Flux increasing
The induced magnetic effect opposes the increase.

Flux decreasing
The induced magnetic effect supports the existing flux direction, opposing the decrease.

Lenz's law and conservation of energy

Lenz's law is consistent with conservation of energy. If the induced effect reinforced the change that produced it, the system could continually amplify the process without the corresponding input of work. In actual electromagnetic induction, the induced response opposes the change, so external work can be required to maintain the change and energy is transferred rather than created from nothing.

Do not memorise: “Lenz's law always opposes the magnetic field.”
Correct: it opposes the change in magnetic flux.

8. Eddy Currents — Assessment-Aware Extension

Syllabus note: Eddy currents are a standard electromagnetic-induction concept in NCERT-style treatment and are widely included in online Chapter 6 resources, but the exact CBSE 2026–27 curriculum wording lists electromagnetic induction, Faraday's laws, induced EMF/current, Lenz's law, self-induction and mutual induction; it does not separately name “eddy currents”. Therefore, learn the basic idea and common applications as enrichment, but do not let it replace the explicitly named syllabus topics.

Eddy currents are circulating induced currents produced inside the bulk of a conductor when the magnetic flux through regions of the conductor changes. Their direction is governed by Lenz's law.

Useful effect
Electromagnetic damping can be used in instruments and braking systems.

Undesired effect
Eddy currents can cause unwanted heating and energy loss in metallic cores, so laminated cores are used in many applications to reduce them.

Exam priority: If time is limited, master magnetic flux → Faraday → Lenz → motional EMF → self-induction → mutual induction first.

9. Induced EMF and Induced Current

An induced EMF can exist even when the circuit is open. An induced current requires a closed conducting path.

Situation	Induced EMF?	Induced current?
Changing flux + open circuit	Yes, an EMF can be induced.	No sustained current because the path is open.
Changing flux + closed circuit	Yes	Yes, subject to circuit resistance/impedance.
Constant flux	No induced EMF from this mechanism	No induced current from electromagnetic induction.

For a simple closed resistive circuit, the magnitude of induced current can be related to the induced EMF by:

I = ε/R

where R is the circuit resistance.

10. Motional EMF — A Moving Conductor

When a conducting rod moves through a magnetic field, its free charges experience magnetic force. Under the standard perpendicular arrangement, this can create a potential difference between the ends of the rod called motional EMF.

ε = Bℓv

This simple form applies when the rod of length ℓ moves with speed v perpendicular to the magnetic field and in the appropriate geometry.

Why does a moving rod develop EMF?

Charges in the moving conductor experience the magnetic force associated with q(v × B). Charges redistribute until the electric force associated with the separation balances the magnetic effect under the steady situation.

Worked example — motional EMF

A rod of length 0.50 m moves at 4.0 m/s perpendicular to a 0.20 T magnetic field. Find the induced EMF across the rod.

Solution: ε = Bℓv = (0.20)(0.50)(4.0) = 0.40 V.

Direction of motional EMF

The direction of charge separation/current depends on the directions of v and B. Use the appropriate right-hand rule or Fleming's right-hand rule consistently rather than guessing the positive end.

11. Motional EMF and Faraday's Law — Same Physics, Different View

The moving-rod situation can be understood in two complementary ways:

Flux viewpoint
Rod motion changes the area of the circuit, so magnetic flux changes. Faraday's law then gives the induced EMF.

Force viewpoint
Moving charges in the rod experience magnetic force q(v × B), producing charge separation and an EMF.

Both descriptions lead to the same physical result when their conditions are applied correctly.

12. Induced Charge — Useful Numerical Result

If a closed circuit of resistance R experiences a change in magnetic flux linkage, the total induced charge that flows can be obtained by combining Faraday's law with I = ε/R.

|q| = N|ΔΦ_B|/R

This result is useful because the time interval can cancel out: the total charge depends on the total change in flux linkage and the circuit resistance, not directly on how slowly or quickly that same change occurs.

Do not confuse: induced EMF depends on the rate of change of flux, while total induced charge in a simple resistive closed circuit depends on the total change in flux linkage.

13. Self-Induction

Self-induction is the phenomenon in which a changing current in a coil changes the magnetic flux linked with that same coil and therefore induces an EMF in the coil itself.

This induced EMF opposes the change in current that produced it, so it is often called a back EMF in circuit contexts.

ε_self = − L dI/dt

Here L is the self-inductance of the coil. Its SI unit is the henry (H).

Meaning of self-inductance

Self-inductance measures how strongly a circuit opposes changes in its own current through electromagnetic induction. A larger L means a larger induced EMF for the same rate of current change.

1 H = 1 Wb/A = 1 V s/A

14. Self-Inductance of a Long Solenoid

For a long air-core solenoid, the magnetic field inside the solenoid is approximately uniform away from the ends:

B = μ₀ n I

where n = N/ℓ is the number of turns per unit length.

The self-inductance of a long air-core solenoid is:

L = μ₀ N²A/ℓ

Equivalently, using n = N/ℓ:

L = μ₀ n² A ℓ

Dependence: For a long solenoid, self-inductance increases with the square of the number of turns and with cross-sectional area, and decreases as the length increases, for the idealised geometry represented by the formula.

15. Energy Stored in an Inductor

When current builds up in an inductor, work is done against the induced EMF. The energy is stored in the magnetic field associated with the inductor.

U = ½ L I²

where U is the stored magnetic energy.

Worked example — stored energy

An inductor of 0.50 H carries a current of 2.0 A. Find the energy stored.

Solution: U = ½LI² = ½ × 0.50 × (2.0)² = 1.0 J.

Common mistake: Do not use U = LI². The factor ½ is essential.

16. Mutual Induction

Mutual induction is the phenomenon in which a changing current in one coil produces a changing magnetic flux linked with a nearby second coil, inducing an EMF in that second coil.

ε₂ = − M dI₁/dt

Here M is the mutual inductance of the pair of coils. Its SI unit is also the henry (H).

Self-induction
Changing current in coil 1 → induced EMF in coil 1.

Mutual induction
Changing current in coil 1 → induced EMF in nearby coil 2.

What affects mutual induction?

Mutual inductance depends on how effectively the magnetic flux produced by one coil links the other coil. It is influenced by factors such as the number of turns, geometry, separation/orientation and the magnetic medium.

17. Mutual Inductance of Two Long Coaxial Solenoids

For two long coaxial solenoids sharing a common length and effective cross-sectional area, an idealised expression is:

M = μ₀ N₁N₂A/ℓ

for an air-core arrangement under the usual ideal assumptions.

Using turns per unit length n₁ = N₁/ℓ and n₂ = N₂/ℓ:

M = μ₀ n₁n₂Aℓ

Interpretation: Greater magnetic coupling between the coils generally means greater mutual inductance. The formula above is an idealised long-coaxial-solenoid result, not a universal formula for arbitrary coil shapes.

18. Self-Induction vs Mutual Induction

Feature	Self-induction	Mutual induction
Cause	Change in current in the same coil.	Change in current in one coil changes flux through another coil.
Induced EMF	ε = −L dI/dt	ε = −M dI/dt
Coefficient	Self-inductance L	Mutual inductance M
SI unit	Henry (H)	Henry (H)
Main idea	A circuit opposes change in its own current.	One circuit can induce an EMF in another coupled circuit.

19. Reciprocity and Mutual Inductance — Conceptual Note

For a pair of appropriately coupled linear coils under the standard passive-network description, the mutual inductance is reciprocal:

M₁₂ = M₂₁ = M

The important Class 12 idea is that mutual induction describes coupling between circuits through changing magnetic flux. Do not confuse the coefficient M with magnetisation M from Chapter 5; they are different physical quantities despite using the same letter in some textbooks.

20. Flux Linkage

For a coil of N turns carrying the same flux Φ_B through each turn, the total flux linkage is:

Flux linkage = NΦ_B

For self-induction in a fixed coil, the flux linkage is proportional to current in the linear idealised case:

NΦ_B = LI

This relationship helps connect the definitions of flux, inductance and induced EMF.

21. High-Yield Problem-Solving Method

Step 1: Draw or mentally identify the loop, conductor and magnetic field.
Step 2: Write Φ_B = BA cos θ if the simple uniform-field expression applies.
Step 3: Identify what changes: B, A, θ, or a combination.
Step 4: Use ε = −NΔΦ/Δt for average EMF or ε = −N dΦ/dt for instantaneous EMF.
Step 5: Use Lenz's law to determine direction.
Step 6: If the circuit is closed and resistive, use I = ε/R where appropriate.
Step 7: Check units and whether the question asks for magnitude, sign or direction.

22. Worked Example — Changing Magnetic Field

Question: A single-turn loop of area 0.20 m² is in a uniform magnetic field perpendicular to its plane. The field changes from 0.50 T to 0.10 T in 0.20 s. Find the magnitude of the average induced EMF.

Solution: Since B is perpendicular to the plane, θ = 0° and Φ = BA.

Change in flux magnitude = A|ΔB| = 0.20 × |0.10 − 0.50| = 0.08 Wb.

Therefore, |ε_avg| = |ΔΦ|/Δt = 0.08/0.20 = 0.40 V.

23. Worked Example — Changing Orientation

Question: A 100-turn coil of area 0.010 m² is in a 0.50 T uniform magnetic field. Its area vector changes from parallel to the field to perpendicular to the field in 0.20 s. Find the magnitude of the average induced EMF.

Solution: Initial flux per turn = BA cos 0° = 0.50 × 0.010 = 0.005 Wb.

Final flux per turn = BA cos 90° = 0.

Magnitude of change in flux linkage = N|ΔΦ| = 100 × 0.005 = 0.50 Wb-turn.

|ε_avg| = 0.50/0.20 = 2.5 V.

24. Common Exam Traps

Trap 1: A strong constant magnetic field does not automatically induce EMF. The relevant requirement is a change in magnetic flux linkage.

Trap 2: In Φ = BA cos θ, θ is measured between B and the area vector, not the plane itself.

Trap 3: Lenz's law opposes the change in flux, not necessarily the magnetic field itself.

Trap 4: Induced EMF can exist in an open circuit, but induced current requires a closed conducting path.

Trap 5: The minus sign in Faraday's law represents the direction given by Lenz's law.

Trap 6: Self-induction concerns the same coil; mutual induction concerns coupling between two coils.

Trap 7: Do not confuse magnetic flux Φ, self-inductance L, mutual inductance M and magnetisation M. Their symbols and meanings are different.

Trap 8: AC generator and transformer are listed under Chapter 7 in the current CBSE 2026–27 syllabus. Do not treat them as Chapter 6 core content merely because some resources place them with NCERT's chapter sequence.

25. Formula & Relationship Map

Concept	Relationship	SI unit / note
Magnetic flux	Φ_B = BA cos θ	Wb
Faraday's law	ε = −N dΦ_B/dt	V
Average induced EMF	ε_avg = −N ΔΦ_B/Δt	V
Induced current	I = ε/R	A, for a simple resistive closed circuit
Motional EMF	ε = Bℓv	V, for the standard perpendicular arrangement
Self-induced EMF	ε = −L dI/dt	V
Self-inductance	L = μ₀N²A/ℓ	H, long air-core solenoid
Energy in inductor	U = ½LI²	J
Mutual-induced EMF	ε₂ = −M dI₁/dt	V
Mutual inductance	M = μ₀N₁N₂A/ℓ	H, ideal long coaxial solenoids
Flux linkage	NΦ_B	Wb-turn
Inductance relation	NΦ_B = LI	Linear idealised case

26. Chapter 6 at a Glance

Topic	What to learn	Exam skill
Electromagnetic induction	Meaning and condition for induced EMF	Conceptual reasoning
Magnetic flux	Φ = BA cos θ; area-vector angle	Formula application
Faraday's laws	Induced EMF and rate of flux change	Concept + numerical
Lenz's law	Direction and conservation-of-energy connection	Direction reasoning
Induced current	EMF in a closed circuit and I = ε/R where applicable	Application
Motional EMF	Moving conductor in magnetic field	Numerical + direction
Self-induction	ε = −L dI/dt; meaning of L	Concept + numerical
Solenoid inductance	L = μ₀N²A/ℓ	Formula application
Energy in inductor	U = ½LI²	Numerical
Mutual induction	ε = −M dI/dt; meaning of M	Concept + numerical
Mutual inductance	Ideal coaxial-solenoid relationship	Formula application
AC generator / transformer	Belongs to Chapter 7 in current CBSE mapping	Study with Alternating Current

27. How to Study Electromagnetic Induction

First: understand magnetic flux and the area-vector angle.
Second: learn Faraday's laws and practise identifying what changes.
Third: master Lenz's law using increasing/decreasing-flux situations.
Fourth: practise motional-EMF questions and direction rules.
Fifth: understand self-induction, inductance and stored magnetic energy.
Sixth: understand mutual induction and the difference between L and M.
Finally: revise formulas, solve chapter numericals and PYQs, then attempt the chapter test after the full Chapter 6 resource cluster is published.

28. Frequently Asked Questions

What is Electromagnetic Induction in Class 12 Physics?

Electromagnetic induction is the production of induced EMF when the magnetic flux linked with a circuit changes.

What is the main formula of electromagnetic induction?

For an N-turn coil, Faraday's law is ε = −N dΦ_B/dt. For average EMF over a finite interval, use ε_avg = −NΔΦ_B/Δt.

What is Lenz's law?

Lenz's law states that the induced current produces a magnetic effect that opposes the change in magnetic flux responsible for the induction.

What is motional EMF?

Motional EMF is the EMF produced when a conductor moves through a magnetic field in a geometry that causes charge separation. For the standard perpendicular rod arrangement, ε = Bℓv.

What is self-induction?

Self-induction is the induction of EMF in a coil due to a change in its own current. The induced EMF is ε = −L dI/dt.

What is mutual induction?

Mutual induction is the induction of EMF in one coil due to a changing current in another magnetically coupled coil.

What is the SI unit of inductance?

The SI unit of both self-inductance and mutual inductance is the henry (H).

Is AC generator part of Chapter 6 for CBSE 2026–27?

No. In the current CBSE syllabus mapping, AC generator and transformer are listed under Chapter 7: Alternating Current. Chapter 6 covers electromagnetic induction, Faraday's laws, induced EMF/current, Lenz's law, self-induction and mutual induction.

How many marks are fixed for Chapter 6?

CBSE assigns 18 marks to Unit IV: Electromagnetic Induction and Alternating Currents, which contains Chapters 6 and 7 together. The curriculum does not prescribe a separate fixed mark allocation for Chapter 6 alone.

29. Chapter 5 Connection

Chapter 5 introduced magnetic fields, magnetic dipoles and magnetic behaviour of matter. Chapter 6 now asks a new question: what happens when the magnetic environment changes? That change leads to electromagnetic induction.

Magnetism and Matter Class 12 Physics Notes is the direct preceding chapter resource.

Magnetism and Matter Formula Sheet + Quick Revision is useful for refreshing the magnetic concepts that Chapter 6 builds upon.

30. Continue the Class 12 Physics Sequence

Chapter 5: Magnetism and Matter

Chapter 4: Moving Charges and Magnetism

Chapter 3: Current Electricity

Chapter 2: Electrostatic Potential and Capacitance

Chapter 1: Electric Charges and Fields

31. Final Exam-Readiness Check

✓ I can explain electromagnetic induction in terms of changing magnetic flux.

✓ I can calculate magnetic flux and identify the correct angle.

✓ I can apply Faraday's law for average and instantaneous EMF.

✓ I can use Lenz's law to determine the direction of induced current.

✓ I can distinguish induced EMF from induced current.

✓ I can solve standard motional-EMF problems.

✓ I can explain self-induction and use ε = −L dI/dt.

✓ I can calculate self-inductance of an ideal long solenoid.

✓ I can calculate energy stored in an inductor.

✓ I can distinguish self-induction from mutual induction.

✓ I can use the mutual-inductance relationship for ideal coupled solenoids.

✓ I know that AC generator and transformer belong to Chapter 7 in the current CBSE 2026–27 mapping.

Source discipline: The official CBSE 2026–27 curriculum is the authority for syllabus scope and unit-level marks. Current competitor resources were used to study search intent, common student questions and content coverage. This page intentionally separates the current CBSE Chapter 6 scope from topics that belong to Chapter 7 or from broader textbook/competitive-exam enrichment.

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Electromagnetic Induction Class 12 Physics Notes 2026–27 | Chapter 6