Title : Simple Circuit
Objective: You connect a battery and a light bulb with wires and create a circuit. The light bulb begins to emit light.
Purpose: To show how a circuit works.
Supplies: Three fresh 1.5 V batteries (flashlight batteries), three battery holders, one 1.5
V light bulb, one 3.0 V light bulb, one 4.5 V light bulb, one light bulb holder, one current visualizer (if available), one switch, and six wires with their ends stripped.
Procedure: Start with one battery and the 1.5 V light bulb. Connect one wire between the battery's positive terminal and one terminal of the light bulb. Discuss that while this single connection is enough to allow positive charge to flow briefly from the battery to the light bulb, that this flow quickly stops. Now connect a second wire from the battery's negative terminal to the other terminal of the light bulb. The light bulb begins to glow.
Discuss why the second wire is so important. Now insert the current visualizer into the circuit between the battery's positive terminal and the light bulb. The visualizer will show that current (the flow of positive charge) always flows through the circuit in one direction, from the battery's positive terminal to the light bulb and back to the battery's negative terminal. Point out that the same electric charge is being used over and over— that it's flowing in a loop, picking up energy from the battery (at a rate of 1.5 J for each coulomb that passes through the battery; hence the label "1.5 V"), releasing that energy in the light bulb, and returning to the battery to make another trip.
Now reverse the battery connections. The flow of current through the rest of the circuit will reverse. This demonstration shows that the battery is responsible for determining the direction of current flow in the circuit. The battery creates the initial charge imbalance that pushes charge through the circuit. Once it's clear how the circuit works, add the switch to the circuit. Show how opening the switch stops the flow of current through the circuit and turns off the light. Discuss the fact that you can insert the switch at any point in the circuit because any break in the circuit stops the current flow.
Now replace the 1.5 V light bulb with the 3.0 V light bulb. It will glow dimly. Discuss the fact that this bulb needs a current of more energetic charges to glow properly. Add a second battery in series with the first battery (connect the negative terminal of one battery to the positive terminal of the other to produce a battery chain with a total voltage of 3.0
V) and note that the light bulb glows much more brightly. Discuss the fact that the current now passes through both batteries and thus receives more energy per charge (3.0 J per coulomb, in accordance with the total battery voltage of 3.0 V). Replace the 3.0 V light bulb with a 4.5 V light bulb and then add a third battery to the chain of batteries.
Once again, the bulb will glow brightly. However, now reverse one of the batteries in the chain. The 4.5 V light bulb will become very dim. Replace it temporarily with the 1.5 V light bulb to show that the chain of batteries is now giving the current flowing through it only 1.5 J per coulomb (1.5 V). The reversed battery is actually taking away energy from the charges passing through it! As a result, the reversed battery is "recharging," although probably not very well because it's not designed to be recharged.

Replace the 1.5 V light bulb with the 4.5 V light bulb and return the battery to its proper situation in thechain. Again, the light bulb will glow brightly.
Science Behind It: Electric charge mustn't accumulate at any point in this arrangement of components. If it did, it would repel any additional charge and the current would stop flowing. By arranging the components in a circuit, the charge can flow continuously through it without accumulating anywhere. The charge simply shuttles energy from the battery to the light bulb's filament. Reversing one battery in the chain causes that battery to extract energy from the current passing through it, rather than adding energy to that current.