|"Resistivity of Various Materials." Cutnell and Johnson. Physics 4th ed. New York: Wiley.||
|Electrical Conductivity & Resistivity for Miscellaneous Metals & Alloys. NDT: Resource Center. 2001.||
|Jaszczak, John A. Graphite 2H Properties. Michigan Tech. 29 October 1998.||
|Products | Fine Carbon. Tokai Carbon Company. 2003.||
So you're doing a lab on conductivity. Your partner had hooked up wires every which way, the power supply is on full blast and the light that symbolizes your failing lab grade is not lighting up. So, like the genius you are, you say to your partner "Why don't you switch that wire?"and you touch the live wire with your pencil. Real smooth rookie. Resistivity is the longitudinal electrical resistance of a uniform rod of unit length and unit cross-sectional area or simply "how much resistance is in this wire?" It is also the reciprocal of conductivity, which means with a low resistivity, you will get a high conductivity.
There are three types of carbon, fullerenes, diamonds, and graphite. The difference between fullerenes, diamonds, and graphite is in their molecular structure. Graphite has a layered molecular structure and there are very weak bonds between the layers, which gives graphite its slippery feel as opposed to diamonds which have rigid bonds between their atoms which allows very little or no movement.
Graphite has many forms and uses in our everyday life. Natural graphite can be found in China, Mexico, Canada, Ukraine, and Brazil, and it is used as a lubricant, filler for flexible graphite, artistry tools, KEVLAR, and of course, pencils. It has a very low resistivity ranging from 9 to 40 µΩm. You could say its resistivity is effectively zero since you just personally found out that carbon was a conductor.
The different kinds of graphite accounts for the range in resistivities. Some graphite is manufactured while some is mined from the above locations. Because of its layered molecular structure, graphite has parallel and perpendicular resistivities, depending on how the graphite is oriented in a circuit. There is also high-density graphite, low-density graphite, granulated, coarse, grease, and every other form that affects the resistivity.
So now you're nursing your slightly burned fingers and after your partner switched the wires (with the power supply off of course), you will pass the lab. Unfortunately, you screwed up royally and will never be allowed in the lab room again.
Africa Belgrave -- 2004