Energy Ball

A small ball about 4 cm across with two metal electrodes that lights up and buzzes when both electrodes are touched at the same time. It is completely self-contained, needing no batteries or external power source, and is designed to show the difference between open and closed circuits in a simple, engaging way. A class can stand in a circle holding hands while two pupils each touch an electrode: when the circuit is complete the ball lights and sounds, and the moment anyone breaks the chain it stops. A built-in field-effect transistor (FET) lets even the tiny current through the pupils' hands trigger it, while the current that drives the light and sound flows only in a separate circuit inside the ball, keeping it safe to use.