The unit in one line
Charge at rest: the force between charges, the field and potential it sets up, and the device built to store it. 4 of Physics's 50 questions over three chapters.
The unit changed shape in 2026. Until the third revision it was "Sound waves, electrostatics and capacitors" and was worth 6; the revision moved sound into Waves and optics and left electrostatics as a unit of four. The three chapters below are now the whole of it.
The chapters
| Chapter | What it covers | Read |
|---|---|---|
| Electric charge and electric field | Charge and its conservation, Coulomb's law and its applications, electrostatic induction, and the field of point charges with its lines | 18 min |
| Field strength, potential and potential energy | Field strength against potential, potential energy and equipotentials, the graphs of each, and Gauss's law with its standard results | 17 min |
| Capacitors | The principle of a capacitor and the parallel-plate formula, series and parallel combinations, stored energy and energy density, and dielectrics | 16 min |
About fifty minutes in all. Four marks over three chapters is a little over one a chapter, so none of the three is safe to skip — but it is also a small enough unit to finish in a single sitting.
Read in this order
Syllabus order, and strictly, because each chapter is the previous one integrated or applied.
Electric charge and electric field first: Coulomb's law and the field of a point charge are the two results the rest of the unit is built from. Field strength, potential and potential energy then moves from the vector quantity to the scalar one — potential is what you get by carrying a charge through the field — and adds Gauss's law, which is the fast route to the field of a sheet, a line or a conductor. Capacitors comes last because a capacitor is a field between two plates and a potential difference across them; the parallel-plate formula falls out of the chapter before it.
One habit is worth forming early: capacitors combine the opposite way round to resistors — series adds reciprocals, parallel adds directly. If you have already read Electrical circuits, keep the two rules side by side rather than trusting memory, because the swap is exactly what the examiner tests.
How it is asked
MEC sets the paper roughly half recall, a third understanding and a fifth application. Recall here is a unit, a definition, or the dielectric constant of a named material. Understanding is why the field inside a conductor is zero, why work done along an equipotential is zero, or what happens to the stored energy when a dielectric is slid into an isolated charged capacitor. Application is an equivalent capacitance, an energy, or a force from Coulomb's law.
Then practise
Each chapter has a fixed-length chapter test under Practice › Topics, drawn from questions written to that chapter's scope. Sit it after reading; a second sitting a week later shows whether it stuck.