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Key concepts Electricity Conductor Insulator
Introduction Electricity powers many of the devices you use every day. Those devices are made up of circuits, ranging from very simple (such as a lamp with a single lightbulb) to very complex (such as in a computer). Try this project to build your own simple circuit and use it to test which common household materials conduct electricity.
Background You probably hear the word electricity a lot, but what does it actually mean? In everyday use electricity typically refers to electrically charged particles (called electrons) moving through metal wires. The flow of electricity is called current. Metals are generally very good conductors, meaning they let current flow easily. Materials that do not let current flow easily are called insulators. Most nonmetal materials such as plastic, wood and rubber are insulators. You will notice this if you have ever plugged something into a wall outlet. The prongs on the plug and the wire inside the cord are metal but they are surrounded by plastic or rubber insulation so you do not get shocked when you touch the cord!
Electricity requires a complete "loop" for current to flow. This is called a closed circuit. That is why wall outlets have two prongs and batteries have two ends (positive and negative) instead of just one. You connect both of them to a circuit and that creates a complete loop. If the loop is broken at all, it becomes an open circuit, and no current will flow.
In this project you will build your own simple circuit by disassembling a flashlight (with permission, of course). You will use your circuit as a tester to determine whether household materials are conductors or insulators. When you connect the circuit to a conductor, you will create a closed circuit and the flashlight bulb will turn on. If you connect the circuit to an insulator, you will still have an open circuit so the bulb will stay off.
Observations and results It may take a bit of work to reverse engineer a flashlight once you have taken it apart. You should be able to get the flashlight to function without its power switch, however, by connecting the battery compartment directly to the bulb using two wires. Adding a third wire allows you to create a "tester". When you touch a metal object with the free wire ends, the bulb should light up just like it usually would. This works because the metal objects are conductors, so they create a closed circuit. When you touch insulating materials such as plastic, rubber and wood, the circuit remains open, so the bulb stays off because no current can flow.
Nonmetal conductive materials can be difficult to find. A graphite pencil core may work for some flashlights. But graphite has a very high resistance compared with metals, so the bulb may appear very dim or not light up at all.
Cleanup Reassemble your flashlight if you need to use it again or keep your homemade conductivity tester!
More to explore Which Materials Are the Best Conductors, from Science Buddies Moving Electrons and Charges, from Physics4Kids Generate Electricity with a Lemon Battery, from Scientific American Science Activities for All Ages, from Science Buddies
This activity brought to you in partnership with Science Buddies
Ben Finio is a senior staff scientist at Science Buddies and a lecturer at the Cornell University Sibley School of Mechanical and Aerospace Engineering. Follow him on Twitter @BenFinio.
Chelsea Harvey and E&E News
Seth Fletcher, Tulika Bose and Jeffery DelViscio
Seth Fletcher, Jason Drakeford, Tulika Bose and Jeffery DelViscio
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