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### Electric Circuit (Melissa Savage)

This interesting device consists of a 1.5-inch ball with two small metal electrodes. When the two electrodes are touched
simultaneously, the device flashes and makes a warbling sound. The Energy Ball utilizes a field effect transistor so even the slightest conduction between the two electrodes activates the Sphere. The Energy ball is completely self-contained and requires no additional batteries or energy source. It is often used to demonstrate closed and open circuits by having two students each touch a different electrode and then activate the device by holding hands. Totally cool!

## What makes the energy ball work?

The Energy Ball utilizes a field effect transistor (FET), so even the slightest conduction between the two electrodes activates the light and noise. The FET acts as an electronic switch. When it senses a decrease in resistance between the ball’s outer terminals, it switches to the ON state. Current then can flow from the battery through the switch and to the light and noisemaker. When in its OFF state, the FET is very close to its instability point, so it is able to switch ON even when the resistance between the terminals is still very high – even through a long line of people.

Students may ask if the current that activates the light and noise is traveling through their hands. It is not. The part of the circuit that contains the battery, bulb, and noisemaker is parallel to the circuit that the students are making with their hands.

Inside the energy ball is a simple circuit that is completely self-contained. By touching both sensors, the circuit is completed by electrons flowing through your body or another conductive material such as a paper clip. Materials that activate theenergy ball are good conductors, meaning they pass electrons easily. Materials that do not activate the energy ball are poor conductors (or insulators), meaning they do not pass electrons easily.

## Things to try:

One Student: Simply hold the ball so that both sensors are touched or, press one sensor with your hand and the other with a paperclip. Try experimenting with other materials (cardboard, plastic, metal) to see which will activate the ball.

Multiple Students: Using two students, have each student touch a sensor, and then hold hands with one another. See how many students can hold hands and still keep the energy ball buzzing. This is an easy way to demonstrate the difference between open and closed circuits – designate one student to be the “switch.” If the switch releases one or both of the hands they’re holding, the ball will stop flashing, representing an open circuit. Holding hands again will resume flashing, and the circuit will be closed.

An Entire Class: For a fun teaching game, try playing a variation of “Duck, Duck, Goose,” with the energy ball. First, form a circle of hands with the energy ball between two students.  One student should be outside the circle, who will be “it.” This student should then go around the circle, pointing to each person in turn and saying either “closed” or “open.” Once a person has been designated “open,” he or she should break the circuit and try to make it around the circle and complete the circuit before the person who was “it”.