= Cavity in a conductor
A <cavity in a conductor> is a void surrounded by an <electrical conductor>; \b[completely enclosed] is the essential qualification in exact <electrostatic shielding> arguments. At <electrostatic equilibrium>, the surrounding connected metal is an <equipotential>. An empty closed <cavity in a conductor> has constant <electric potential> and zero <electric field>, even if the metal is isolated and charged. An occupied closed <cavity in a conductor> generally has a nonzero <electric field>; its inner-wall total <electric charge> cancels the total <electric charge> of the internal sources. These are distinct statements, illustrated by <Faraday's ice pail experiment>.<Intermediate College Physics by Richard Fitzpatrick/Ideal Conductors>[Richard Fitzpatrick, Ideal Conductors, equations 2.127 and the following uniqueness argument: a charge-free enclosed cavity]{ref}
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