Electrostatic Fields, Surface Charge, and Cavities in Conductors

All flashcards

Conduction electron

An electron that can move through a conducting material over macroscopic distances.

Polarization in a conductor

Separation of positive and negative charge as mobile charges redistribute.

Electrostatic equilibrium in a conductor

A state with no ongoing charge redistribution and zero field within the metal.

Induced charge on a cavity wall

For a charge $q$ in a cavity, the inner wall carries total charge $-q$.

Field outside an isolated conducting sphere

The field is the same as that of a point charge at the sphere’s center.

Quiz questions

1. A charge $+q$ is placed inside the cavity of an initially neutral conductor. What total charge is induced on the cavity wall?Answer: $-q$
2. Why is the electric field at a conductor’s surface perpendicular to the surface in electrostatic equilibrium?Answer: A tangential component would move free surface charges.
3. An isolated conducting sphere has radius $R$ and net charge $q$. For $r>R$, what is the field equivalent to?Answer: The field of a point charge $q$ at the center.
4. Two large parallel conducting plates have equal and opposite surface charge densities of magnitude $\sigma$. What is the field magnitude between them in the idealized model?Answer: $\sigma/\varepsilon_0$
5. What did the null result from connecting concentric conducting shells to a sensitive electrometer provide a precise test of?Answer: Possible departures from Coulomb’s inverse-square law.