Physics · Ch 1 — Electrostatics
Electrostatic shielding
Electrostatic shielding
One of the most useful practical consequences of a conductor's electrostatic properties concerns a hollow conductor -- a conductor with an empty cavity carved out of its interior. Using Gauss's law, together with the fact that the field inside the solid part of any conductor at equilibrium is zero (established in section 1.7.1), it can be shown that the electric field inside such a cavity is also exactly zero, provided no charge is deliberately placed inside the cavity itself -- and this remains true no matter how strong an external electric field is applied to the outside of the conductor, and no matter what shape the cavity or the outer conductor takes. Physically, whatever external field tries to penetrate the conductor induces charges on the conductor's outer surface that exactly cancel the field throughout the conducting material and, in turn, leave the enclosed cavity completely field-free. This complete blocking of an external electric field from reaching the interior of a hollow conductor is called electrostatic shielding, and it is the physical principle behind the Faraday cage, used to protect sensitive electronic equipment (and, in a …
What this figure shows. A solid conducting block with a hollow cavity carved out of its interior is drawn sitting in a strong external electric field, whose field lines are shown terminating on the conductor's outer surface and never penetrating through into the hollow cavity at all -- the region inside the cavity is shown completely free of field lines, however strong the external field outside the conductor is made. A small Gaussian surface drawn just inside the cavity's boundary confirms, via the zero enclosed charge and the zero field established on the conductor's own inner surface, that th …