Schooling · Class 12 · Physics · Electromagnetic Induction · Chapter on a page
CBSE Class 12 · Physics · NCERT Physics Part-I
Electromagnetic Induction: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
This note's current text has no applied fact-check on record.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- Magnetic flux
- Faraday's law of electromagnetic…
- Lenz's law
- Motional emf
- Eddy currents
- Self-inductance
- Mutual inductance
- Formulas and facts
- Φ = B A cos θ
- ε = −dΦ/dt
- ε = −N (dΦ/dt)
- ε = Blv
- L = μ₀ n² A l
- ε₂ = −M (dI₁/dt)
- U = (1/2) L I²
- Watch out for
- Forgetting the negative sign in…
- Using total magnetic field instead…
- Confusing flux (Φ = BA cos θ) with…
- Ignoring the number of turns when…
- Thinking induced current appears…
What this chapter is about
Electromagnetic induction is the phenomenon where a changing magnetic flux through a conducting loop produces an electromotive force (emf) in that loop. This chapter builds on your understanding of magnetic fields from earlier work and introduces how electricity can be generated from magnetism. The discovery by Michael Faraday in 1831 revolutionised technology and led to electric generators, transformers and countless devices we use today.
Key ideas
- Magnetic flux through a surface equals the product of the magnetic field component perpendicular to the surface and the area: Φ = B A cos θ, measured in weber (Wb).
- Faraday's law of electromagnetic induction states that the magnitude of induced emf in a loop equals the rate of change of magnetic flux through the loop: |ε| = |dΦ/dt|.
- Lenz's law gives the direction of induced emf: the induced current opposes the change in flux that causes it, ensuring energy conservation.
- Motional emf arises when a conductor moves through a magnetic field; for a rod of length l moving with velocity v perpendicular to field B, the emf is ε = Blv.
- Eddy currents are circulating currents induced in bulk conductors when flux through them changes; they cause heating and are used in induction furnaces and electromagnetic braking.
- Self-inductance (L) of a coil measures how the coil opposes change in its own current; the induced emf is ε = −L (dI/dt), and the SI unit is henry (H).
- Mutual inductance (M) describes flux linkage between two coils; an emf is induced in one coil when current in the neighbouring coil changes.
- Energy stored in an inductor carrying current I is U = (1/2) L I², analogous to energy stored in a capacitor.
Formulas and facts to remember
- Magnetic flux: Φ = B A cos θ, where θ is the angle between B and the area normal.
- Faraday's law: ε = −dΦ/dt (the negative sign represents Lenz's law).
- For N turns: ε = −N (dΦ/dt).
- Motional emf for a rod: ε = Blv (when B, l and v are mutually perpendicular).
- Self-inductance of a solenoid: L = μ₀ n² A l, where n is turns per unit length, A is cross-sectional area and l is length.
- Mutual inductance: ε₂ = −M (dI₁/dt).
- Energy stored in an inductor: U = (1/2) L I².
- 1 weber = 1 volt × 1 second; 1 henry = 1 weber per ampere.
Common mistakes
- Forgetting the negative sign in Faraday's law → the sign encodes Lenz's law and shows opposition to flux change; always interpret direction using it.
- Using total magnetic field instead of the perpendicular component → include cos θ when the field is not normal to the surface.
- Confusing flux (Φ = BA cos θ) with field (B) → flux depends on area and orientation, not just field strength.
- Ignoring the number of turns when applying Faraday's law → multiply dΦ/dt by N for a coil with N turns.
- Thinking induced current appears even when the circuit is open → an emf is induced, but current flows only if a closed path exists.
Quick revision
- Induced emf equals rate of change of magnetic flux: ε = −N (dΦ/dt).
- Lenz's law: induced effects always oppose the cause producing them.
- Motional emf for a rod: ε = Blv when B, l and v are mutually perpendicular.
- Self-inductance opposes change in current; unit is henry (H).
- Energy in an inductor: U = (1/2) L I².
- Eddy currents arise in bulk conductors and cause heating; laminated cores reduce them.