PURPOSE: To illustrate magnetohydrodynamic forces.

DESCRIPTION: A shallow bowl of copper sulfate solution is placed in the (downward) magnetic field of a medium-strength horseshoe magnet. An electron current is created between the negative electrode band around the circumference of the bowl and the positive electrode at the center of the bowl. The resulting vxB force on the electrons creates counterclockwise rotation of the copper sulfate solution. Small pieces of paper are dropped onto the surface of the rotating liquid as an indicator.

Click your mouse on the photograph above to see an mpeg video of the action.

Strangely, this device is described in a paper (see references) under the title "An Interesting Exhibit." And guess what? It is!

SUGGESTIONS: See Question of the Week #184 for suggestions on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 5H30.50) See Demonstration Reference File for further information on magnetohydrodynamic devices and their applications.

EQUIPMENT: Magnetohydrodynamic device with copper sulfate solution, horseshoe magnet, and power supply.

SETUP TIME: 5 min.