The Line of Resistance: Using a Graphite Pencil to Explore the Electrical Properties of Materials and Circuits

The purpose of "The Line of Resistance" is to provide teachers with creative, inexpensive, hands-on/minds-on ideas that illustrate electrical properties of materials and circuits. The ideas include activities, as well as creative drama exercises, intended to supplement regular curriculum materials. There are detailed teacher instructions for learning and performing the activities and dramas, as well as mathematical explanations.

The publication is directed to high school and college science teachers. Some aspects of the publication are also appropriate for middle school (after Ohm's Law has been introduced), but the mathematics and explanations may be beyond the conceptual level of most middle school students. The student instructions are somewhat open-ended, allowing ample opportunity for students to construct their own knowledge of electrical properties with, of course, help from the teacher.

The exploratory activities in this booklet correspond with recommendations of National Science Education Standards.

This unit addresses the following National Science Education Standards (NSES) for grades 5-8:
Physical Science

    Properties and Changes in the Properties of Matter
    • "A substance has characteristic properties, such as density, a boiling point and solubility, all of which are independent of the amount of the sample."
    Transfer of Energy
    • "Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei and the nature of a chemical. Energy is transferred in many ways."
    • "Electrical circuits provide a means of transferring electrical energy when heat, light, sound and chemical changes are produced."
This unit addresses the following National Science Education Standards for grades 9-12:
Physical Science
    Interaction of Energy and Matter
    • "In some materials, such as metals, electrons flow easily, whereas in insulating materials such as glass they can hardly flow at all. Semiconducting materials have intermediate behavior. At low temperatures some materials become superconductors and offer no resistance to the flow of electrons."
    This unit also addresses the NSES standards that call for more emphasis on:
    • "Learning subject matter disciplines in the context of inquiry ..."
    • "Investigations over extended periods of time."
    • "Using multiple process skills - manipulation, cognitive, procedural."
    • "Doing more investigations in order to develop understanding, ability, values of inquiry and knowledge of science content."

Along with teacher activities and student handouts are suggestions for teaching "The Line of Resistance". There are ideas for classroom organization, introductory exercises, assessments and creative dramas.

Many aspects of "The Line of Resistance" relate to students' everyday lives, and making connections between the two can further learning. Graphite pencils are familiar to students. Drawing resistors and circuits with pencils allows the student freedom to explore and discover relationships for themselves.

Developed by Dr. Lawrence Woolf, a physicist at General Atomics, in collaboration with the Institute for Chemical Education, the Line of Resistance kit is available for purchase through the Institute for Chemical Education.

Teachers can use this kit to teach their students how to measure the electrical properties of materials and circuits using a graphite pencil, a piece of paper and an ohmmeter. The contents are outlined below:

  • Activities
    • The electrical resistivity of graphite
    • The dependence of resistance on dimensions - intrinsic and extrinsic properties of materials
    • Resistance of series circuits
    • Resistance of parallel circuits
    • Open and short circuits
    • The electrical resistivity of silver ink
    • A precise measurement of the electrical resistivity of a metal
    • The resistance of a banded carbon resistor
    • The electrical breakdown field of air
    • The path of least resistance - lightning rod demonstration
  • Teaching Strategies
  • Creative Dramas
    • Conductor vs semiconductor vs insulator
    • Length and width dependence of resistance
  • Summary and assessment ideas
  • Summary of Scientific Principles

Addenda to the Line of Resistance

The addenda contain additional experiments and creative dramas that complement the original unit now sold by the Institute for Chemical Education at the University of Wisconsin . There are a new series of experiments and problems on lightning safety that also use a graphite pencil and a piezoelectric sparker. In a new section on superconductors, students measure electrical losses in "superconducting" and normal magnets that they make using copper wire and the graphite pencil. They also fabricate a superconducting magnet with a "persistent switch." A creative drama and assessment about electrical conduction by electrons and holes extends the creative dramas described in the original module. THIS ADDENDA IS FREE! DOWNLOAD USING THE LINK ABOVE