Electricity and Magnetism

Pluses and Minuses

This exhibit illustrates the phenomena of static electricity. Pieces of Styrofoam are placed on a metal plate which is a few inches below a copper plate. A plastic paddle disk is rubbed on a wool cushion and then placed on top of the copper plate, and the Styrofoam chips “dance.” Touching the copper plate while the paddle is lying on top of it will cause the Styrofoam chips to settle on the lower plate. Removing the paddle will cause the chips to dance again. When the disk is rubbed on the cushion, electrons move off the cushion to the disk. When the disk is placed on the conductive copper plate, the plate becomes negatively charged and causes some of the Styrofoam chips, which are positively charged, to rise up to the copper plate.