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Electromagnetic Induction

Faraday's law, motional emf and inductance. Nearly half its questions have numeric answers.

Questions in the bank
90
q/paper in 2025–26
0.68
Numeric answer
46%
Notes pages
4

Tier: Long tail

When you’ll see it

A flux that changes through a field, an area or an angle, or a conductor moving or turning across a field, and the emf, current or charge that follows.

How this chapter is tested

Almost every question here comes down to one law: the emf is the rate at which the flux changes. The work is in seeing what changes — the field, the area, the angle, or a conductor cutting across the field — and writing that change down before reaching for a formula.

The pages run from a loop in a changing field, to rods on rails and loops crossing the edge of a field, to coils, rods and discs that rotate, and end with self and mutual inductance and LR circuits. The arithmetic is short. Marks are lost on factors: an angle taken from the plane instead of the normal, the wrong component of the earth's field, the half in ½Bωl², rpm left unconverted, or a current change that crosses zero.

Many questions want a typed number, so a lost factor has no option to expose it. The force on a current in a field comes from Moving Charges and Magnetism, and a coil turning at a steady rate is the source behind Alternating Current.

The sub-skills

The distinct skills inside the chapter, in the order to learn them.

  • Flux, Faraday's law and Lenz's law

    Write Φ = NBA cos θ with θ from the normal, differentiate in time, and let the current oppose the change; the charge that flows is NΔΦ/R and does not depend on the time taken.

  • Motional emf on rods, rails and loops

    A rod cutting a field gives Blv with the field component it cuts; on rails the drag B²l²v/R sets a terminal speed; a loop has an emf only while an edge crosses a field boundary.

  • Rotating coils, rods and discs

    A coil spinning at ω gives NBAω sin ωt, largest when its plane lies along the field; a rod turning about one end gives ½Bωl², and a disc the same between axle and rim.

  • Inductance and LR circuits

    Back emf −L dI/dt, mutual emf −M dI/dt, stored energy ½LI², and a current that grows or decays with time constant L/R.

Traps to expect

Distractor shapes this chapter reuses. The Traps page covers the ones that cut across chapters.

  • Plane or normal

    Flux takes the cosine of the angle from the normal. An angle given from the plane of the loop needs its sine instead.

  • The wrong component of the earth's field

    The dip is measured from the horizontal. Wings and a horizontal fan cut only the vertical component B sin δ; a falling horizontal wire cuts only the horizontal one, B cos δ.

  • Forgetting the half

    A rod turning about one end gives ½Bωl², because its pieces move at speeds from zero to ωl. A fan's emf is that of one blade, however many blades it has.

  • A change that crosses zero

    A current going from −2 A to +2 A changes by 4 A. A field that reverses changes the flux by 2NBA, not by zero.

Learn it before you drill it

This chapter has full teaching notes — foundations, worked examples, self-checks and a mastery check for each page. Read the notes once, then drill page by page below.

Electromagnetic Induction notes

Drill every Electromagnetic Induction question

90 questions from the bank, across 4 subtopics.

Drill the 90 questions

Drill one subtopic at a time

The 4 subtopics, in teaching order.

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