  We study small conducting particles and thin films in an oscillating
longitudinal electric field. We find the charge, current, and field
distribution in the particle, the polarizability and the electric dipole
absorption. We account for Thomas-Fermi screening by adding a Fick's diffusion
term to Ohm's law. Alternatively, we describe a particle as a dielectric body
with a non-local dielectric constant which is derived in a microscopic
linear-response theory. We show that both approaches are equivalent.
