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Ohm's Law

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Fried Pencil

Fried Pencil

Credit: Juliancolton
Source: http://commons.wikimedia.org/wiki/File:Closeup_of_pencil_graphite.JPG
License: CC BY-NC 3.0

This pencil “lead” is actually made of graphite. Graphite is a crystalline form of the element carbon.

Amazing but True!

  • Elements that can conduct electric current are generally metals. However, the nonmetal carbon in the form of graphite is a good conductor of electricity.
  • Credit: Mike Beauregard
    Source: http://www.flickr.com/photos/31856336@N03/7140603137/
    License: CC BY-NC 3.0

    Graphite can be found in crystal form. This particular specimen is from Baffin Island in Canada [Figure2]


  • Watch this video to see how connecting a pencil to a battery causes current to flow through the pencil and “fry” it:


Show What You Know

At the link below, learn more about carbon, current, and short circuits. Then answer the questions that follow.

  1. Why is graphite, a nonmetal, a good conductor of electricity?
  2. What is Ohm’s law? How does Ohm’s law explain why the pencil burns in the video above?
  3. How could you reduce the amount of current flowing through the pencil in the video?
  4. What is a short circuit? Give an example of how a short circuit might occur.
  5. How does the demonstration in the video show the danger of a short circuit?

Image Attributions

  1. [1]^ Credit: Juliancolton; Source: http://commons.wikimedia.org/wiki/File:Closeup_of_pencil_graphite.JPG; License: CC BY-NC 3.0
  2. [2]^ Credit: Mike Beauregard; Source: http://www.flickr.com/photos/31856336@N03/7140603137/; License: CC BY-NC 3.0

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