Which Materials are the Best Conductors?

Introduction

The existence of electricity has been known since the ancient Greeks used to rub pieces of amber with fur to make static electricity. Benjamin Franklin is credited with the first demonstration that the electricity in lightening and static electricity are the same in his famous, but very dangerous, experiment. It took hundreds of years for thinkers, inventors and scientists to learn how to control and harness the power of electricity. 

The first great achievement was the discovery of the concept of a circuit in 1800 by an Italian named Alessandro Volta. He showed that electricity flows through a circuit, and that a circuit needs to be complete, or closed, in order to work. He also invented the first battery, and we use the word Volt to identify the units of electricity.

The next great discovery was by a German school teacher named Georg Simon Ohm in 1826, who had been a student of Volta. He discovered that some materials slowed down, or resisted, the movement of electricity. He found out that there was a relationship between the amount of electricity in a circuit, the movement of electricity through the circuit and the resistance of the circuit. The movement of electricity through a circuit is described by Ohm's Law, which relates the voltage (measured in volts, abbreviated V) to the current (measured in amperes, abbreviated A) and to the resistance (measured in ohms, abbreviated with a capital Greek letter omega: Ω).

Electricity flows very well through some materials, and not so well through others. Materials that allow electricity to flow freely are called conductive materials. Materials that make the flow of electricity difficult are called insulators. Conductive materials have a very low resistance, and insulators have a very high resistance. Both conductors and insulators are common materials used to build circuits. The most common example is a copper wire (a conductor) that is covered by a plastic coating (insulator) used to make a circuit.

What other types of materials are conductors and insulators? In this experiment you will build your own simple light bulb circuit and use it to test different materials to see if they are conductors or insulators. By putting different materials in the circuit and observing the brightness of the bulb, you can make a list of conductors and insulators.

Terms and Concepts

To do this type of experiment you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• electricity
• circuit
• electrons
• current
• resistance
• conductor
• insulator

Questions

• How do electrons flow through different materials?
• How is resistance measured?
• How can different materials be tested for conductivity?

Bibliography

Here are some great Internet resources available:

• Surf this website for kids by the First Energy Corporation. Find out about electricity, history, efficiency and safety while having fun too! They also provide an excellent glossary:
  First Energy Corp., 2005. "Electric Avenue." Akron, OH. [12/13/05] http://www.firstenergycorp.com/kids/
• Thelwell, A., 2005. "The Blobz Guide to Electrical Circuits." Staffordshire University, UK. [12/13/05] http://www.andythelwell.com/blobz/
• The best place to buy parts for exploring and playing with electricity will probably always be Radio Shack. Find all of your supplies on the online catalog:
  Radio Shack Corp., 2005. "Cables, Parts & Connectors" Fort Worth, TX. [12/13/05] http://www.radioshack.com/category/index.jsp?categoryId=2032058
• This site has a java applet you can use to make printable, color graphs of your data:
  NCES, 2006. "Create a Graph," National Center for Education Statistics (NCES) U.S. Dept. of Education. [accessed: 3/3/06 ]http://nces.ed.gov/nceskids/createagraph/

Materials and Equipment

To do this experiment you will need:

• several small pieces of different materials to test (aluminum foil, paper clips, wood, plastic, rubber bands, string, etc...);
• 6 V battery (e.g., Radio Shack 23-560);
• 3 wire leads with alligator clips at both ends (e.g., Radio Shack 278-1156; they can be any color, but to tell them apart we will call them 'red,' 'black,' and 'yellow');
• 6 V light bulb with wire leads (e.g., Radio Shack 272-1140);
• flat, insulating surface (like a cutting board).

Experimental Procedure

1. Set up your circuit board that you will use to test your materials. You will need three pieces of wire with an alligator clip at each end. You can make your own, or you can buy an insulated alligator clip lead set from a store like Radio Shack.
2. Attach one clip of the black wire to the (−) battery terminal by clipping the alligator clip securely to the terminal.
3. Attach one clip of the red wire to the (+) battery terminal by clipping the alligator clip securely to the terminal.
4. Attach the other end of the black wire to one of the light bulb leads.
5. Attach the one clip of the yellow wire to the other light bulb lead.
6. You will connect your different materials between the free ends of the red wire and the yellow wire.
7. Make a data table for your results, including a place to write the type of material, source of material and the brightness of the light bulb:
   

   Type of Material	Source of Material	Brightness of Bulb (e.g., off, dim, bright)

8. Next, place the first material into the circuit by clipping one end to the free red clip and the other end to the free yellow clip.
9. Does the light bulb light up? How bright is it? Write down the results in the data table.
10. Repeat steps 8 and 9 for each different material you want to test. Remember to write down, in your data table, how bright the light bulb appears for each material you test.
11. How do the different materials compare? Do some materials have make the light bulb glow brightly while others only make it glow dimly? Do some materials not make the light bulb light at all?
12. Categorize the materials according to your results. Put materials with high brightness readings (high brightness = high conductivity = low resistance) into the conductor category. Put materials with 'dim' brightness readings into the 'poor conductor' category. Put materials with 'off' brightness readings (no brightness = high resistance = low conductivity) into the insulator category.
    

    Insulators	Poor Conductors	Conductors