Knowledge Organiser: Electromagnetic Induction
Part of Electromagnetic Induction · GCSE GCSE Physics revision
This topic summary covers Knowledge Organiser: Electromagnetic Induction within Electromagnetic Induction for GCSE Physics. Revise Electromagnetic Induction in Magnetism for GCSE Physics with 13 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 15 of 15 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 15 of 15
Practice
13 questions
Recall
12 flashcards
Knowledge Organiser: Electromagnetic Induction
Key Principles
- Changing magnetic flux → induced EMF → current (if circuit complete)
- Static field = no induction
- Lenz's law: induced current opposes the change
- Energy conserved: work in = electrical energy out
Increasing Induced EMF
- Faster movement
- Stronger magnet
- More turns of wire
- Larger coil area
Generator Key Facts
- Coil rotates in magnetic field
- Slip rings + brushes → AC output
- EMF max when coil parallel to field
- EMF zero when coil perpendicular to field
- Kinetic energy → electrical energy
Generator vs Motor
- Generator: motion → electricity (slip rings)
- Motor: electricity → motion (split-ring)
- Same structure, reverse energy flow
- Generator uses induction; motor uses motor effect
Key Equations
- Vs ÷ Vp = Ns ÷ Np (transformer voltage ratio)
- Vp × Ip = Vs × Is (transformer power conservation)
- Induced EMF ∝ rate of change of magnetic flux
- Step-up transformer: Ns > Np → Vs > Vp
Common Mistakes
- Saying a stationary magnet induces a voltage: The magnetic field must be changing — only a moving magnet (or changing current) induces an EMF in a nearby conductor
- Confusing slip rings and commutator: Slip rings → continuous contact → AC output (generators); split-ring commutator → current reversal → DC output (motors)
- Getting step-up/step-down wrong: Step-up transformer has more turns on the secondary (Ns > Np) — voltage increases; step-down has fewer secondary turns — voltage decreases
- Thinking transformers work with DC: Transformers only work with AC — a steady DC current produces a constant (not changing) magnetic field, so no EMF is induced
- Applying transformer equation to power: A step-up transformer increases voltage but decreases current proportionally — power input equals power output (assuming 100% efficiency)
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