Which equations do I need for electricity and magnetism?

The core equations are charge equals current times time (Q = I t), Ohm's law (V = I R), electrical power (P = V I) and the transformer equation (Vp over Vs equals Np over Ns). Know the unit of each quantity: coulombs, amps, volts, ohms and watts.

What is the difference between the motor effect and electromagnetic induction?

The motor effect is the force on a current-carrying wire in a magnetic field, with the direction given by Fleming's left-hand rule, and it drives electric motors. Electromagnetic induction is the reverse: a changing magnetic field induces a voltage in a coil, which is how generators and transformers work.

Why does the National Grid use transformers?

Step-up transformers raise the voltage for transmission, which reduces the current and so reduces the energy lost as heat in the cables. Step-down transformers then lower the voltage again for safe use in homes and businesses.

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Electricity, magnetism and electromagnetism: study guide - CCEA GCSE Physics

A study guide to the electricity and magnetism topic of CCEA GCSE Physics: charge, current, voltage and resistance, series and parallel circuits, I-V characteristics, mains electricity and safety, the motor effect and electromagnets, and electromagnetic induction with generators and transformers.

Generated by Claude Opus 4.89 min readCCEA Unit 2Updated 2026-06-14

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this topic covers
How it is examined
The equations to recall
How to revise it

Electricity, magnetism and electromagnetism is the largest topic in Unit 2. It blends circuit calculations with the magnetic effects of currents and the induction that powers generators and transformers.

What this topic covers

Charge, current, voltage and resistance - $Q = It$ , Ohm's law $V = IR$ , and how to connect meters.
Series and parallel circuits - the current and voltage rules and how total resistance changes in each.
I-V characteristics - the graphs for an ohmic resistor, a filament lamp and a diode.
Mains electricity and safety - AC and DC, the three wires, fuses and earthing, and electrical power $P = VI$ .
The motor effect and magnetism - magnetic fields, electromagnets, the motor effect and Fleming's left-hand rule.
Electromagnetic induction and transformers - induction, the AC generator, transformers and the transformer equation.

How it is examined

Expect circuit calculations using Ohm's law and the series and parallel rules, graph questions on I-V characteristics, the fuse and earth safety explanation, field and motor-effect questions, and transformer calculations. Method and unit marks reward clear working.

The equations to recall

Charge: $Q = It$ .
Ohm's law: $V = IR$ .
Electrical power: $P = VI$ .
Transformer equation: $\dfrac{V_p}{V_s} = \dfrac{N_p}{N_s}$ .

How to revise it

Drill circuit calculations. Be fluent with Ohm's law and the series and parallel rules.
Learn the I-V graphs. Know the shape and explanation for the resistor, lamp and diode.
Rehearse the safety explanation. Write out how the earth wire and fuse protect a user.
Master Fleming's left-hand rule. Practise predicting force directions for the motor effect.
Practise transformer questions. Use the turns ratio and identify step-up or step-down.

Work through the linked dot points for full worked answers and exam-style questions on each part of the topic.

Sources & how we know this

CCEA GCSE Physics specification — CCEA (2017)