Hair dryers, toaster ovens, flashlights, and televisions sets all work thanks to electrons. Without electrons -- or, more precisely, the flow of electrons -- millions of people would lead very different lives. This flow of electrons, also known as electric current, is essentially the same whether it is generated by a nuclear power plant or by an AA battery.

In order for electric current to flow, three important conditions must be met. One of these is the presence of a material, usually in the form of a wire or cable, that conducts electricity. This means that electrons can move, or flow, easily through the material, not staying locked on any particular atom by atomic forces. Some materials, called conductors, contain loosely held electrons, allowing for this free flow. In contrast, materials called insulators hold onto their electrons more strongly and resist the flow of current through them.

The second requirement for the flow of electric current is a power source itself. Whatever its form, a source of electric current creates what is called a voltage difference, a kind of pressure that pushes the electrons through the circuit.

Lastly, electric current requires a closed circuit. This is a length of conducting material connected at each end to a power source passing through the "load, " or the object that needs the current to operate. The circuit allows a direct, uninterrupted flow of electrons from the power source and back -- a complete circular connection with no beginning or end.

The steadiness tester created in this video segment fulfills all of the requirements of an electric circuit -- so long as the person being tested is less than steady. This last requirement, in fact, is the one that allows the device to function as a steadiness tester. In other words, the steadiness tester operates only when a cast member accidentally touches the inside of the wire loop to the tester. This action closes the circuit, causing electricity to flow and the alarm to sound.