IGCSE Physics: Electricity and Magnetism

Electricity and magnetism is the topic students fear most — circuits look abstract, and the right-hand-rule gymnastics are intimidating. But every past paper follows the same blueprint: one calculation with Ohm's law or power, one circuit analysis, one qualitative electromagnetic induction question. Drill that blueprint and the topic becomes one of the most predictable.

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What you need to master

1Current, charge and potential difference — definitions and units.
2Ohm's law, I-V characteristics of components (resistor, filament lamp, diode).
3Series and parallel circuits, potential dividers.
4Electrical power, energy and cost of running appliances.
5Magnetic fields around bars, solenoids and current-carrying wires.
6The motor effect and Fleming's left-hand rule.
7Electromagnetic induction, transformers and the UK mains.

Key formulas

V = IR

Q = It

E = QV

P = VI = I²R = V²/R

E = Pt

Vp/Vs = Np/Ns (transformer)

VpIp = VsIs (ideal transformer)

Examiner tips

•Show the full sub-calculation for power and energy — examiners reward method marks even if the final answer is wrong.
•In parallel circuits, total resistance is LESS than the smallest branch. State this explicitly when asked.
•For transformers, always explain the "alternating current → changing magnetic field → induced voltage" chain.

Common mistakes to avoid

•Using V = IR with parallel resistors without first finding the correct branch voltage.
•Saying a transformer "makes" electricity — it transfers energy, it does not generate it.
•Confusing direct current and alternating current when discussing transformers and mains.