Surface charge distribution on conductors means that in electrostatic equilibrium, all excess charge on a solid conductor sits on its outer surface, leaving the electric field inside the conductor at zero and the field at the surface perpendicular to it (AP Physics 2, Topic 10.3).
Put extra charge on a solid metal sphere and something interesting happens. The charges are free to move, they all repel each other, and they keep shoving each other around until they're as far apart as possible. The only way that ends is with every bit of excess charge sitting on the outer surface and zero charge left in the interior. That settled state is called electrostatic equilibrium.
Two consequences come directly from the CED and show up constantly on the exam. First, the electric field everywhere inside the conductor is zero. If it weren't, free charges would still feel a force and keep moving, so it wouldn't be equilibrium yet. Second, at the surface, the field points perpendicular to the surface. Any sideways (parallel) component would push charges along the surface, which again would mean charges are still moving. The surface arrangement is whatever pattern makes both of those things true.
This idea lives in Unit 10 (Electric Force, Field, and Potential), specifically Topic 10.3, and it's spelled out in learning objective 10.3.B, which asks you to describe the electric field generated by charged conductors and insulators. The essential knowledge is blunt about it. Excess charge on a solid conductor in electrostatic equilibrium is distributed on the surface, the field within the conductor is zero, and the field at the surface is perpendicular to the surface. It also gives you a powerful shortcut for spheres. Outside an isolated sphere with a spherically symmetric charge distribution, the field is identical to that of a point charge with the same net charge sitting at the center. That one fact lets you reuse everything you know about point-charge fields from 10.3.A on charged spheres, which is exactly the kind of model-transfer reasoning AP Physics 2 rewards.
Keep studying AP® Physics 2 Unit 10
Electrostatic equilibrium (Unit 10)
Surface charge distribution isn't a separate rule, it's the end result of electrostatic equilibrium. Charges in a conductor move freely, so they rearrange until no charge feels a net force, and the only arrangement that pulls that off puts all excess charge on the surface with zero field inside.
Electric field of point charges (Unit 10)
Once charge settles on a sphere's surface symmetrically, the field outside the sphere is exactly the field of a single point charge at the center. So a charged metal sphere problem is secretly a point-charge problem from 10.3.A, just with the field starting at the surface instead of at a point.
Charge distribution in insulators (Unit 10)
Insulators are the contrast case in 10.3.B. Their charges can't move, so excess charge stays spread throughout the volume wherever it was placed, and the field inside an insulator is generally not zero. The conductor's special behavior comes entirely from charge mobility.
No released FRQ uses this exact phrase, but the underlying facts from 10.3.B are classic multiple-choice and short-answer material. Expect stems like "What is the electric field at the center of a charged conducting sphere?" (answer: zero) or "Where does excess charge reside on a solid conductor in electrostatic equilibrium?" (answer: the outer surface). You may also need to sketch or rank fields, and the giveaways are that field lines stop at a conductor's surface, meet it at 90 degrees, and never pass through the interior. On free-response questions, the high-value move is justification. Don't just say the interior field is zero, explain that mobile charges would keep moving if any field existed inside, so equilibrium forces the field to zero. That cause-and-effect reasoning is what earns the points.
Conductors and insulators handle excess charge in opposite ways, and the CED tests both. In a conductor, charges move freely, so all excess charge migrates to the outer surface and the interior field is zero. In an insulator, charges are locked in place, so excess charge stays distributed throughout the material and the interior field is generally not zero. If a question says "charged rubber sphere" instead of "charged metal sphere," you cannot assume the charge is on the surface or that the inside field vanishes.
In electrostatic equilibrium, all excess charge on a solid conductor sits on its outer surface, with none in the interior.
The electric field everywhere inside a conductor in electrostatic equilibrium is zero, because any nonzero field would still be pushing free charges around.
At the surface of a charged conductor, the electric field is perpendicular to the surface; a parallel component would make surface charges keep moving.
Outside an isolated, symmetrically charged sphere, the field is identical to that of a point charge with the same net charge located at the sphere's center.
Insulators behave differently because their charges can't move, so excess charge stays distributed throughout the volume instead of rushing to the surface.
It's the principle from Topic 10.3 that in electrostatic equilibrium, all excess charge on a solid conductor resides on the outer surface, leaving zero electric field inside the conductor and a field perpendicular to the surface just outside it.
It's zero whenever the conductor is in electrostatic equilibrium, which is the condition AP Physics 2 questions almost always assume. If charges are still moving (like in a current-carrying wire), the conductor isn't in electrostatic equilibrium and the rule doesn't apply.
Like charges repel and they're free to move in a conductor, so they push apart until they're as spread out as possible. The maximally spread-out arrangement puts everything on the outer surface, and at that point no charge feels a net force, which is the definition of equilibrium.
A conductor's excess charge moves to the outer surface and its interior field is zero. An insulator's charges are fixed in place, so excess charge stays distributed throughout the material, per essential knowledge under 10.3.B. Read the problem carefully to see which material you're given.
Yes, but only outside the sphere. The CED says the field outside an isolated sphere with spherically symmetric charge equals the field of a point charge with the same net charge at the center. Inside the conductor, the field is zero, not the point-charge value.
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