Electrostatic equilibrium
Also called Electrostatic equilibrium of a conductor
Electrostatic equilibrium is the state an object reaches once its charges have stopped moving. In a conductor it means no electric field inside the conducting material, all excess charge on the surface, and the whole surface at one potential.
Nothing is drifting any more, and every conductor result follows from that. C: E&M EK 10.1.A.3.i says the time interval to reach it is so short as to be negligible, so on an exam a conductor is already there.
Four conductor statements worth holding as a set, each with its CED source:
- The field within the conductor is zero, since all excess charge sits on the surface and the interior carries no net charge (EK 10.1.A.4; AP Physics 2 EK 10.3.B.1).
- Excess charge resides entirely on the surface, driven there by mutual repulsion (EK 10.1.A.2).
- Every point on the surface reaches the same potential, so the conductor becomes an equipotential surface (EK 10.1.A.3.ii).
- The field is perpendicular to the outer surface (EK 10.1.A.5; AP Physics 2 EK 10.3.B.1.i).
That is a working set, not the complete list. The same learning objective also gives you higher charge density at points and edges (EK 10.1.A.3.iii), polarization in an external field (EK 10.1.A.6), and electrostatic shielding by a closed conducting shell (EK 10.1.A.7).
It is not a conductor-only word. EK 10.3.B.2 in AP Physics 2 and EK 8.3.B.2 in C: E&M say that while in electrostatic equilibrium, an insulator has excess charge spread through its interior as well as its surface, and the field within it may be nonzero. Equilibrium means the charges stopped, not that the field vanished.