  The influence of the Coulomb distortion for quasi-elastic (e,e') scattering
on highly charged nuclei is investigated in distorted wave Born approximation
for electrons. The Dirac equation is solved numerically in order to obtain
exact electron continuum states in the electrostatic field generated by the
charge distribution of an atomic nucleus. Different approximate models are used
to describe the nucleon current in order to show that, at high electron
energies and energy-momentum transfer, the influence of Coulomb distortions on
(e,e') cross sections can be reliably described by the effective momentum
approximation, irrespective of details concerning the description of the
nuclear current.
