Electromagnetic Induction Notes for NEET, JEE Main 2027: Key Points

Electromagnetic Induction is Chapter 6 of NCERT Class 12 Physics Part I and part of Unit 14, Electromagnetic Induction and Alternating Currents, in both the NEET UG 2026 and JEE Main 2026 syllabi. These notes cover magnetic flux, Faraday’s and Lenz’s laws, motional emf, eddy currents, self and mutual inductance and the AC generator, with a free notes PDF.

Electromagnetic Induction Notes for NEET and JEE Main

Section-wise key points from NCERT Chapter 6, formula tables, most-asked facts and common mistakes for 2027 revision.

Electromagnetic Induction at a Glance

Topics follow the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025 and the JEE Main 2026 syllabus released by the National Testing Agency (NTA); both stay the reference until the 2027 syllabi are out. Full lists: NEET syllabus and JEE Main syllabus.

Experiments of Faraday and Henry

Around 1830, Michael Faraday in England and Joseph Henry in the USA showed independently that a changing magnetic field induces a current in a coil.

• Moving a bar magnet towards or away from a coil connected to a galvanometer deflects the galvanometer; the faster the motion, the larger the deflection.
• Moving a current-carrying coil towards or away from a second coil has the same effect, so it is the relative motion that matters.
• Switching the current on or off in one coil (with a tapping key) induces a momentary current in a nearby stationary coil.
• Inserting an iron rod along the axis of the coils increases the deflection.

Magnetic Flux and Faraday’s Law

Faraday’s law: the magnitude of the induced emf in a circuit equals the time rate of change of magnetic flux through it.

• Magnetic flux through an area A in a uniform field: Φ_B = B·A = BA cos θ. For a non-uniform field, add B·dA over the surface.
• Flux is a scalar. SI unit: weber (1 Wb = 1 T m²).
• Induced emf: ε = −dΦ_B/dt; for a closely wound coil of N turns, ε = −N dΦ_B/dt.
• If the circuit is closed, a current I = ε/R flows.
• Flux can be changed by changing B, changing the shape or area of the coil, or rotating the coil in the field.

Lenz’s Law and Conservation of Energy

Lenz’s law (Heinrich Lenz, 1834): the polarity of the induced emf is such that the induced current opposes the change in magnetic flux that produces it.

• The negative sign in Faraday’s law expresses Lenz’s law.
• Lenz’s law follows from conservation of energy. If the induced current helped the change, energy could be created without any work, which is impossible.
• The mechanical work done against the opposing force is converted into electrical energy and finally dissipated as Joule heat.
• In an open circuit an emf is still induced across the ends, but no current flows.

Motional Emf

A conductor moving through a magnetic field has an emf induced across it because of the Lorentz force on its free charges.

• Rod of length l moving with velocity v perpendicular to a uniform field B: ε = Blv.
• Motional emf can be explained without Faraday’s law, using the Lorentz force on the moving charges. An emf is also induced in stationary charges by a time-varying field, which the Lorentz force alone cannot explain.
• Rod of length l rotated with angular velocity ω about one end, perpendicular to B: ε = ½Bωl² (NCERT Example 6.6 works this out).

Eddy Currents (older NCERT Edition)

Eddy currents are the currents induced in bulk pieces of conductors when the magnetic flux through them changes; they swirl like eddies in water.

• By Lenz’s law they oppose the motion or the change that produces them.
• They heat the conductor and waste energy, for example in transformer cores.
• They are reduced by using laminated cores (thin insulated sheets) or by cutting slots in metal plates, which lengthen the path of the current.
• Uses: magnetic (electromagnetic) braking in trains, electromagnetic damping in galvanometers, induction furnaces and electric power meters.

Inductance: Mutual and Self

Inductance is the ratio of flux linkage to current. It depends only on the geometry of the coil and the permeability of the medium. Its SI unit is the henry (H).

• M₁₂ = M₂₁, a general result shown in NCERT for coaxial solenoids.
• Inductance is a scalar with dimensions [M L² T⁻² A⁻²]. The henry is named after Joseph Henry.
• Self-inductance is electrical inertia, the analogue of mass: it opposes both the growth and the decay of current.
• Energy stored in an inductor: U = ½LI², like ½mv² for kinetic energy.
• Magnetic energy density: u_B = B²/(2μ₀), compared with ½ε₀E² for an electric field.

AC Generator

An AC generator converts mechanical energy into electrical energy by rotating a coil in a magnetic field, which keeps changing the flux through it.

• Parts: a coil (armature) mounted on a rotor shaft, rotated in a uniform field, with its ends connected to the external circuit through slip rings and brushes.
• With angular speed ω, flux Φ = NBA cos ωt and the emf ε = NBAω sin ωt = ε₀ sin ωt, where ε₀ = NBAω.
• The emf is maximum when the plane of the coil is parallel to B (θ = 90° or 270°), where the flux is zero but changing fastest.
• Since ω = 2πν, ε = ε₀ sin 2πνt. The frequency of rotation is 50 Hz in India (60 Hz in some countries such as the USA).
• In most commercial generators the coils are held stationary and the electromagnets are rotated.
• The mechanical energy comes from falling water (hydro-electric), steam produced using coal or other sources (thermal) or nuclear fuel (nuclear power generators).
• NCERT credits Nicola Tesla with developing the machine.

Most-asked Facts for NEET and JEE Main: Electromagnetic Induction

Revise these one-line facts from the NCERT chapter just before the exam.

• Faraday (England) and Henry (USA) discovered electromagnetic induction around 1830.
• Φ = BA cos θ; 1 Wb = 1 T m².
• ε = −N dΦ/dt; the minus sign is Lenz’s law.
• Lenz’s law is a consequence of conservation of energy.
• Motional emf ε = Blv; rotating rod ε = ½Bωl².
• Eddy currents are reduced by laminated cores; used in magnetic braking and galvanometer damping.
• ε = −M dI₂/dt; M₁₂ = M₂₁.
• Self-inductance of a solenoid L = μ₀n²Al (μᵣμ₀n²Al with a core).
• Inductance unit henry; dimensions [M L² T⁻² A⁻²].
• Energy in an inductor ½LI²; magnetic energy density B²/(2μ₀).
• AC generator emf ε = NBAω sin ωt; peak ε₀ = NBAω.
• Peak emf occurs when the flux through the coil is zero.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Linking induced emf to the flux itself. It depends on the rate of change of flux, not on its value.
• Saying the induced current opposes the magnetic field. It opposes the change in flux.
• Expecting a current in an open loop. An emf is induced, but current needs a closed circuit.
• Placing the peak emf of a generator at maximum flux. The emf is largest when the flux is zero and changing fastest.
• Writing Blv for a rotating rod. For rotation about one end, use ½Bωl².
• Thinking inductance depends on the current. Like capacitance, it depends only on geometry and the medium.
• Assuming eddy currents are dropped from the exams. They were removed from the rationalised NCERT chapter but are still in both syllabi.

Electromagnetic Induction Notes PDF and Related Pages

Download the AglaSem Class 12 Physics unit notes (Magnetic Effects of Current and Magnetism, and EMI and Alternating Current; key notes and important questions with answers) free: View PDF

• All chapters: Physics notes for NEET and JEE Main
• Full topic list: NEET syllabus and JEE Main syllabus
• Practice: NEET question papers and JEE Main question papers
• Source text: NCERT Chapter 6 (NCERT, Class 12 Physics Part I)

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