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Next exam on November 14 – 15, 2026:
All concepts

Electromagnetic Induction

电磁感应

Magnetic flux and its change, the condition for and direction of an induced current (Lenz's law), Faraday's law of induction, and the emf of a rod cutting field lines.

10 real-exam questions · 4 sittings19 in mock papers23 practice

Formulas

  • Definition of magnetic flux

    Definition
    Φ=BS\Phi=BS

    Applies when：Requires S perpendicular to B; otherwise use the component of B normal to S

  • Faraday's law of induction

    Law
    ε=nΔΦΔt\varepsilon=n\frac{\Delta\Phi}{\Delta t}

    Applies when：The emf follows the rate of change of flux, not the flux itself; direction by Lenz's law

  • Motional emf

    Formula
    ε=BLvsin⁡θ\varepsilon=BLv\sin\theta

    Applies when：ε=BLv when B, L and v are mutually perpendicular; θ is the angle between v and B

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

  1. CSCA Physics December 2025 Past Paper
    The international units for magnetic flux density BB and magnetic flux are respectively ( ).
    • A．Tesla, Weber
    • B．Ampere, Volt
    • C．Pascal, Hertz
    • D．Joule, Watt
    Show answer & solution

    Answer: A

    1 Magnetic flux density B has unit Tesla (T). Magnetic flux Φ\Phi has unit Weber (Wb).
    See it in the full CSCA Physics December 2025 Past Paper
  2. CSCA Physics April 2026 Past Paper
    In a 50 -turn coil, the magnetic flux changes uniformly from 0.2 Wb to 0.6 Wb in 0.1 s . The induced EMF is
    • A．200 V
    • B．20 V
    • C．100 V
    • D．50 V
    Show answer & solution

    Answer: A

    ε=NΔΦΔt=50×0.6−0.20.1=50×4=200 V\varepsilon = N \frac { \Delta \Phi } { \Delta t } = 50 \times \frac { 0.6 - 0.2 } { 0.1 } = 50 \times 4 = 200 \mathrm {~V}.
    Take the full CSCA Physics April 2026 Past Paper — timed & graded
  3. CSCA Physics March 2026 Past Paper
    Parallel rails connected by R; wire ab slides frictionlessly in a perpendicular uniform field. When ab moves right at constant speed, which is correct? Question 46 diagram
    • A．Constant speed continues after removing force
    • B．ab experiences both pulling force and Ampère force
    • C．Increasing R increases pulling force
    • D．Greater speed means smaller pulling force
    Show answer & solution

    Answer: B

    Moving wire generates ϵ\epsilon, current, and Ampère force opposing motion. Constant speed requires a pull to balance the Ampere force (B). A: removing force → deceleration. C: larger R → less current → less Ampère force → less pull needed. D: faster → larger ϵ→\epsilon \rightarrow more current → more Ampère force → more pull needed. Answer: B.
    Take the full CSCA Physics March 2026 Past Paper — timed & graded

Real-exam evidence

Recorded past-paper appearances are listed below; online verification is labelled separately.

10 questions across 4 sittings1 of 4 sittings available to verify free online

19 questions across 6 mock papers — our own papers, so a coverage signal rather than real-exam evidence

23 related practice questions availablePractise free: Electromagnetic Induction

Sitting evidence comes from the CSCA past papers on record; questions whose original paper is missing are excluded, and sprint papers are deliberately not counted.

Glossary

electric current

Related concepts

Magnetic Field, Ampère Force and Lorentz Force