Turning on a light bulb with nothing but a battery and a wire is the simplest way to show how electricity flows. Electricity will flow out of the negative terminal of the battery, through the light bulb and back into the positive terminal of the battery. As the electricity passes through the light bulb, it is forced through a filament made of tungsten. As the filament heats up, it glows and gives off light, proof that electricity is flowing through the circuit.
Stretch the wire out in front of you and select a spot about an inch from one end.
Press your razor blade down into the wire, just hard enough to cut through the rubber insulation, not hard enough to sever the wire. Roll the wire over so that you have cut a circle around the wire. Push your razor blade toward the end of the wire to expose an inch of wire without insulation.
Repeat the same process on the other end of the wire, except this time expose about three inches of wire.
Wrap the end of the wire with three inches exposed around the metal threads near the bottom of the light bulb. Make sure the exposed wire is only touching the metal threads.
Set your 9-volt battery on the table in front of you with the two contacts pointing up.
Grab the other end of the wire, the end that isn't attached to the bulb, in one hand. Make sure you are holding the insulated portion. Grab the bulb end of the light bulb in your other hand. Touch the wire to one of the 9-volt battery contacts, then touch the small metal disc at the bottom of the light bulb to the other contact. The electricity will light up the bulb.
This process only works if the light bulb and battery are close to the same voltage. If you were to try this with a common household light bulb, which uses 120 volts, even though the circuit would complete there would not be enough voltage flowing through the line to make the filament glow.