Capacitance and Dielectrics

Lesson

Part 1 — how conductors hold charge, and the capacitor: a device that stores charge and energy.

In this lesson you will

Explain why the field inside a charged conductor is zero and charge resides on its surface
Define capacitance and derive the capacitance of a parallel-plate capacitor
Derive and use the equivalent capacitance of series and parallel combinations

Diagram

Conductors in electrostatics

In a conductor at equilibrium (no current):

E = 0 inside: otherwise the free electrons would move.
Any excess charge resides on the outer surface (Gauss’s theorem: a surface just inside encloses no charge).
The whole conductor is at one potential; just outside, E is normal to the surface.
Free charges (conduction electrons) move through a conductor; bound charges in an insulator can only shift slightly within atoms.

Check your understanding

Decide whether the statement is true or false.

True or false1 mark

True or false? In electrostatic equilibrium, the electric field inside the metal of a charged conductor is zero.