Simplifying Circuits
By Crystal Jeter
Product Developer
The alarm sounds, the lights are turned on, and a cellphone is checked. During this introduction to the day, a student has already experienced electrical circuits at least 3 times. While students continue to use electricity throughout the day, most probably have only a superficial understanding of how circuits work. The following simple inquiry activities can help.
Materials
The following materials are suggested, and many others can easily be incorporated:
- Miniature Light Bulbs
- Economy Switches
- Alligator Clips
- Battery Holders
- Insulated Hook-Up Wire
- Wire Strippers
- Multimeters
- Light Bulb Holders
- D Cell Batteries (1.5 V)
- Everyday Items to Test for Conductivity (e.g., Coins, Pencils, Erasers, Plastic Chips, Fabric, Paper Clips)
Procedures
Complete the first activity to introduce the basics of a circuit. After that, conduct the others in any order, as class time and interest allow.
- What does it take to make a bulb light? Have students discover what is needed to create a simple circuit. Give each student or team 1 battery, 1 light bulb, and 1 wire with an alligator clip at each end. Challenge students to make the bulb light. Instruct them to record every configuration that they attempt and whether that attempt was successful. After everyone has successfully lit the bulb using only the bare-bones items, distribute battery holders, bulb holders, and additional hook-up wire. Have the students use these items in their circuits. The simple circuit they make can be modified for all additional activities. Note: Depending on the type of bulb and battery holders you use, you may or may not need alligator clips on your hook-up wires.
- Does it matter if the battery is turned the other direction? Have students turn the battery so that the polarity is reversed. Students should see that the bulb lights either way.
- What happens if there is more than 1 battery? Tell students to add an additional battery to the circuit in series. Students will see that if multiple batteries’ polarities are oriented oppositely then the bulb will not light. Students will also see that increasing the number of batteries increases the brightness of the bulb. You may wish to have students test the 1-battery and 2-battery circuits with a voltmeter so they can see the additive nature of voltage. Note: If students increase the voltage beyond the capacity of the bulb, the filament will burn out and the bulb will no longer work. (In testing these activities, I tried a series of 3 batteries, and the filament burned out after 1 hr, but many variables are at work, and your results may differ.)
- Can 2 bulbs light at the same time on the same circuit? Tell students to add additional bulbs in series to their circuit and examine the results. Students should observe changes in the brightness of the bulb(s). Additional bulbs adds resistance to the current, causing multiple bulbs to be dimmer than a single bulb would be.
- What if the wires are different lengths? Have students change the lengths of wires involved in their circuits. If longer wires are used, the light bulb is dimmer. With shorter wires, the bulb is brighter. Even though the metal in the wires is chosen for conductivity, it still offers some resistance.
- What will conduct electricity? Guide students to determine whether materials are conductors or insulators. Students can use their setup to create a circuit tester. By touching 2 leads to a variety of items, they can see whether the bulb lights. If the bulb lights, then the material has completed the circuit; i.e., the current has been conducted through it. If the bulb does not light, then the material is not a good conductor and may be an insulator. Students should see that metals tend to be good conductors.
- How do switches work? Have students add switches to their circuits. Challenge students to determine how the switches make the light bulb stop and start glowing. After students examine the switches that you provide, have them devise their own switches and try them out.
- In a house, why don’t all of the lights on 1 circuit go out when 1 light is turned off? Have students compare parallel and series circuits. Challenge students to create a system in which 2 or 3 bulbs glow brightly on a single circuit. Students should see that a parallel circuit is the only way to accomplish this task. Then, have them create a 2-bulb series circuit and a 2-bulb parallel circuit, remove 1 of the bulbs from each, and compare what happens. With the bulbs wired in parallel, 1 bulb can remain lit when the other is removed from the circuit.
After students have completed each activity, hold a class discussion of their observations and techniques. Discussing their methods and observations helps students remember the experience and the concepts.
