THE FIELDS OF MOVING CHARGES — Edward Purcell & David Morin
Physics — E&M · drift-velocity-in-seawater
Problem
Drift velocity in seawater *
The resistivity of seawater is about 0.25 ohm-meter. The charge carriers are chiefly Na+ and Cl− ions, and of each there are about 3⋅1026 per m3. If we fill a plastic tube 2 meters long with seawater and connect a 12 volt battery to the electrodes at each end, what is the resulting average drift velocity of the ions?