La charge sur un conducteur

In electrostatic equilibrium, the electric field inside a conductor must be zero. By Gauss's law, if there were charge inside the conductor's body, an electric field would exist there. Since this violates equilibrium conditions, all net charge must move to the conductor's surface, where it can arrange to cancel any external fields inside the material.

When a charge is enclosed in a hollow conductor's cavity, the inner surface acquires an induced charge opposite in sign to the enclosed charge. This occurs because electrostatic equilibrium requires zero net charge inside the conductor's material. The induced charge on the inner surface ensures the electric field within the conductor remains zero.

A conductor polarizes in response to external charges, inducing charges on both its inner and outer surfaces. The distribution depends on the conductor's geometry and the location of external charges. At equilibrium, the charge arrangement creates an electric field that exactly cancels external fields throughout the conductor's body.

For a hollow conductor with no enclosed charge, Gauss's law applied to a surface inside the conductor's material shows zero enclosed charge, so no charge appears on the inner surface. The conductor remains in electrostatic equilibrium with zero electric field inside its material, and any net charge resides only on the outer surface.

The net charge inside a closed conducting container is always zero. If a charge is enclosed and finds a conducting path to the container's surface, it flows outward. If isolated, the enclosed charge induces an equal and opposite charge on the inner surface, maintaining zero net charge within the conductor's material itself.

Each cavity induces opposite charges on its inner surface based on the enclosed charge. The outer surface then acquires a net charge equal to the sum of all enclosed charges. The specific distribution on the outer surface depends on the conductor's geometry, but the total charge always resides on the surfaces, never inside the conductor's material.

A car's metallic body acts as a conductor in electrostatic equilibrium. When struck by lightning, charge flows to the outer surface. Since the electric field inside the conductor must remain zero, Gauss's law confirms no charge accumulates on inner surfaces or cavities, protecting occupants inside.