2.2 Charge Distribution

Conductors vs. Insulators

In conductors, charge carriers (electrons) move freely, so excess charge redistributes itself across the surface until electrostatic equilibrium is reached, making the electric field inside zero. In insulators, charges are fixed in place and stay where they're deposited, so charge distributes non-uniformly and can remain localized in patches.

Charge on Conductor Surfaces

At equilibrium, excess charge on an isolated conductor resides entirely on its outer surface, not the interior. Charge density is higher at sharply curved regions (like points) and lower on flatter areas, since like charges repel and spread apart to minimize repulsion while staying on the surface.

Charging Methods

Charging by friction transfers electrons between materials via contact. Charging by induction rearranges charges in a nearby conductor without direct contact, using an external charged object to attract or repel electrons, often followed by grounding to leave a net charge. Polarization in insulators involves slight realignment of molecular charges without net electron transfer.

Key terms

Conductor charge equilibrium

Excess charge resides entirely on the outer surface; the electric field inside the conductor is zero.

Insulator charge behavior

Charges are fixed in place and remain localized where deposited rather than spreading out.

Charging by induction

Using a nearby charged object to rearrange charges in a conductor without direct contact, often followed by grounding.

Charging by friction

Transferring electrons between two materials through direct contact and rubbing.

Charge density at curved surfaces

Charge density is higher at sharply curved or pointed regions of a conductor's surface than on flat areas.

Try an AP-style question

Where does excess charge reside on a conductor in electrostatic equilibrium?

1. On its outer surface
2. Only at its lowest point
3. At its center
4. Evenly throughout its volume