| This exhibit demonstrates
the motor effect. When an electrical current passes through a magnetic
field there is a force on the charges that make up the current.
If those charges happen to be trapped in a wire, there is a force
on the wire. In this exhibit the visitor touches a wire to a copper
disk which sits between the poles of a large magnet. The current
(electrons) flows from the edge of the disk to the center of the
disk. If contact with the disk is made such that current flows through
the magnetic field, the disk starts to spin.