Which statement best distinguishes conductors from insulators in electrostatics?

Which statement best distinguishes conductors from insulators in electrostatics?

• A. Conductors fix charges; insulators allow movement; E inside a conductor is zero
• B. Conductors allow free movement of charges; insulators hold charges fixed; E inside a conductor is zero at equilibrium
• C. Both allow free movement
• D. Neither conducts electricity

Answer: (B)

In electrostatics, the key distinction is how charges behave: conductors let charges move freely and rearrange themselves in response to fields, while insulators hold charges fixed in place. Because charges in a conductor can roam, they migrate until any internal electric field is canceled, so the electric field inside the conductor becomes zero at electrostatic equilibrium. Insulators, with charges that are bound, do not rearrange to cancel internal fields, so there can be a nonzero field inside if charges are placed there. This is why the correct statement says conductors allow free movement of charges, insulators hold charges fixed, and the electric field inside a conductor is zero at equilibrium. The other ways of phrasing it get this behavior wrong in some way: one reverses which materials allow movement, another says both allow movement, and another says neither conducts, which isn’t true.

In electrostatics, the key distinction is how charges behave: conductors let charges move freely and rearrange themselves in response to fields, while insulators hold charges fixed in place. Because charges in a conductor can roam, they migrate until any internal electric field is canceled, so the electric field inside the conductor becomes zero at electrostatic equilibrium. Insulators, with charges that are bound, do not rearrange to cancel internal fields, so there can be a nonzero field inside if charges are placed there. This is why the correct statement says conductors allow free movement of charges, insulators hold charges fixed, and the electric field inside a conductor is zero at equilibrium. The other ways of phrasing it get this behavior wrong in some way: one reverses which materials allow movement, another says both allow movement, and another says neither conducts, which isn’t true.