Pencil Graphite Resistor

Discover how graphite conducts electricity by measuring the resistance of a pencil—demonstrating that everyday materials can be resistors.

Overview

Pencil "lead" isn't actually lead—it's graphite, a form of carbon that conducts electricity. In this simple project, you'll expose the graphite core of a pencil and measure its resistance using a multimeter. You'll discover that resistance changes based on the distance between measurement points, demonstrating how resistance depends on the length of a conductor.

Components Needed

  • 1x Pencil

Instructions

  1. Gather Your Materials

    For this project, you'll need a standard pencil and a multimeter capable of measuring resistance (ohms). Any pencil will work, but softer lead pencils (2B, 4B, 6B) have more graphite and will show lower resistance readings.

  2. Expose the Graphite Core

    Carefully shave away the wooden casing along one side of the pencil to expose a strip of graphite about 2-3 inches long. You can use a knife, sandpaper, or a pencil sharpener held at an angle. The goal is to create an exposed graphite surface where you can place the multimeter probes at different points.

  3. Measure Resistance at Wide Spacing

    Set your multimeter to measure resistance (Ω). Place the two probes on the exposed graphite, spacing them far apart (about 2 inches). Press firmly to ensure good contact. Note the resistance reading—in this example, we measured 43.1 ohms with the probes spaced widely apart.

  4. Measure Resistance at Closer Spacing

    Now move the probes closer together and measure again. You should see a lower resistance reading! In this example, moving the probes closer resulted in a reading of 35.0 ohms. This demonstrates that shorter conductor length means lower resistance—a fundamental principle of Ohm's Law.

Challenges

  • Measure resistance at several different distances and create a graph of resistance vs. distance
  • Compare different pencil grades (2H, HB, 2B, 6B)—which has the lowest resistance?
  • Calculate the resistivity of graphite using your measurements and the formula ρ = R × A / L
  • Try connecting the pencil in a circuit with an LED—can you light it up?