  In a watt balance experiment, separate measurements of magnetic force and
induced electric potential in a conductor in a magnetic field allow for a
virtual comparison between mechanical and electrical powers, which leads to and
an accurate measurement of the Planck constant. In this paper, the macroscopic
equations for the magnetic force and the induced electric potential are
re-examined from a microscopic point of view and the corrective terms due to a
non-uniform density of the conduction electrons induced by their interaction
with the magnetic field are investigated. The results indicate that these
corrections are irrelevant to the watt balance operation.
