Ions in a solution are subject to a uniform electric field. If each ion carries charge q and has radius R, then the ionic current I due to the applied field will depend on q and R as :

The electric force on an ion is F_e = qE. Assuming Stokes' law for the viscous drag force in a solution, F_d = 6πηRv, where η is viscosity, R is the ion's radius, and v is its drift velocity. In steady state, F_e = F_d, so qE = 6πηRv. The drift velocity is v = qE / (6πηR). The ionic current I is proportional to the charge of each ion (q), the number density of ions (n), their drift velocity (v), and the cross-sectional area (A): I = nqvA.