Electromagnetic Circuit

Electromagnetic Circuit (telegraph):

Glue the foam to the cardboard. Stick the tip of the nail into it so that it is upright. Unwrap the large loop of a paper clip so that the short loop remains with a long wire down. Stick this paper clip into the foam so that the short loop is positioned closely above the nail. When the switch is closed the short loop will be attracted to the nail head and a tap will be heard. The paper clip should spring back and tap back each time the switch is closed. This may require some adjusting. Angle the paper clip stem back a bit so the foam can push it back.

Closing the switch will cause current to flow through the coated wire around the nail. The magnetic field associated with the current will be concentrated on the nail and will induce magnetism in the nail. The nail will attract the paper clip above it and a tap will be heard. The taps are controlled by opening and closing the switch.