Electrostatics
Unit 1. Covers Electric charge and Coulomb’s law; Electric field and dipoles; Gauss’s theorem; Electric potential; Conductors, dielectrics and polarisation; Capacitors.
About this unit
Electrostatics is the study of charges at rest. It starts with Coulomb’s law for the force between two charges, builds up the ideas of electric field and electric potential, uses Gauss’s theorem to find fields quickly for symmetric charge distributions, and ends with conductors, dielectrics and capacitors. These ideas are the base for current electricity, circuits and much of modern electronics, so this unit is worth learning carefully.
How to prepare
- Memorise the core formulas: F = kq₁q₂/r², E = kq/r², V = kq/r, U = kq₁q₂/r, C = ε₀A/d, U = ½CV².
- Learn the field formulas from Gauss’s theorem for a line, a sheet and a shell, with how each depends on distance.
- Practise unit-checking: N/C equals V/m, and 1 F = 1 C/V.
- Solve series and parallel capacitor problems until they feel routine.
- Link ideas: field is force per unit charge, potential is energy per unit charge, and E = –dV/dr connects them.
Topics in this chapter
Electric charge and Coulomb’s law
Conservation of charge, Coulomb’s law and superposition.
6 questionsElectric field and dipoles
Field lines, field of a point charge and a dipole, and torque on a dipole.
5 questionsGauss’s theorem
Electric flux and fields of a wire, plane sheet and spherical shell.
5 questionsElectric potential
Potential of a point charge, dipole and system of charges; equipotential surfaces and potential energy.
5 questionsConductors, dielectrics and polarisation
Free and bound charges and dielectrics.
5 questionsCapacitors
Capacitance, series and parallel combinations, dielectrics and energy stored.
5 questions