Science Buddies: "Ask an Expert"

I am working on my science fair project, and I require assistance. I have searched multiple times for ways to measure conductivity of solids. I am testing the following solids, Aluminum, lead, copper, iron, and carbon. I am testing these solids at different temperatures, to determine how conductivity is affected. My problem is, that I cannot find a method of measuring and quantifying the conductivity. Thanks.

One thing you could do is create a simple lightbulb circuit, and place the material you are testing somewhere along the circuit. Based on how bright the light in the bulb is, you can get a general idea of how conductive the materials are relative to one another. If you want to get more precise, you could even use an electrical measuring device to tell exactly how much current is getting through.


Or, if you are trying to tell how conductive the materials are to temperature, you could use is a basic grill thermometer, and use this to measure how long it takes the opposite side of your conductive surface to reach a certain temperature.

NOTE: Be very careful when handling stripped wires and other electrical tools. Be sure to only attempt these experiments under the supervision of an adult.

From Wikipedia, here is a definition of electrical conductivity, and the formula relating its dependence on temperature.
http://en.wikipedia.org/wiki/Electrical_conductivity
I'm sure you already know this from your research. The problem, if how to measure the conductivity of those solids.

A simple electrical ohm meter, won't be accurate enough to measure a difference in resistance of the wires of short lengths. I would think all the very conductive substances (copper, aluminum) would measure at a resistance of zero.

More accurate measurement of electrical resistance can be made using a method known as four terminal sensing:
http://en.wikipedia.org/wiki/Four-terminal_sensing

I'm sure meters that measure this way exist, but are likely quite expensive compared to a simple multimeter.

A question for any of my EE colleagues on the board is are there any inexpensive ways to measure in this fashion? Any alternative methods?

Hi bryphan!

If you input "How does temperature affect conductivity?" to answers.com, you get two direct hits. Each has some preliminary text, and some pointers (that look like spheres with paper clips).

The first one points to:
http://www.masterflex.com/techinfo/tech ... .htm&ID=78

The second one points to:
http://www.kittiwake.com/Default.aspx/Page/KB/KB/242

Following the two hits above, there are a wide range of net resources.
Notes:

1. The exact wording of your input to answers.com, or any other search engine, may have a big impact on your result. So, some experimentation may be needed.
2. Beware of sites that are just trying to sell you something. In answers.com, these are supposed to br segregated under "Sponsored Links." But, they occasionally leak into "Web Results."