A copper sulfate solution is placed in a container that contains coaxial cylindrical copper electrodes, as indicated in the picture.
An electric field is created by connecting a battery across the electrodes as shown. A magnet field is created by immersing a magnet in the center of the solution as shown.
Uncharged pollen grains are sprinkled in the area between the electrodes. They are observed to circulate counterclockwise when viewed from above. You hypothesize that they are carried along by the circulation of ions in the solution due to the electric and magnetic forces that act on those ions.
Can you tell if the charge on the circulating ions is positive or negative? Explain.