We derive an Ohm's law for single-particle motion in a current sheet, where the magnetic field reverses in direction across the sheet. The result is considerably different from the resistive Ohm's law often used in MHD studies of the geomagnetic tail. We extend our single-particle analysis to obtain a self-consistency relation for a current sheet which agrees with previous results. Our results are applicable to the concept of reconnection in that we obtain the electric field parallel to the current for a one-dimensional current sheet with constant normal magnetic field. Dissipated energy goes directly into accelerating particles within the current sheet.