Grade Four

Amazing Pencil Resistor Science Project: Build Your Own Variable Resistor with a Pencil in 5 Steps

Aravinth R · August 4, 2026 4 min read
Amazing Pencil Resistor Science Project: Build Your Own Variable Resistor with a Pencil in 5 Steps

The Pencil Resistor Science Project: Build Your Own Variable Resistor

Introduction

Electricity may seem complicated, but this simple activity makes it easy to understand. Using a pencil, a battery, and an LED, you can explore how electricity flows through a circuit.Amazing Pencil Resistor Science Project: Build Your Own Variable Resistor with a Pencil in 5 Steps

As the path through the graphite becomes longer, the LED becomes dimmer, showing how electrical resistance controls the flow of current. This fun experiment introduces an important electronics concept using everyday materials.

Overview

The key material in this activity is graphite, the black core inside a pencil. Graphite is a form of carbon that can conduct electricity, although not as well as metals like copper.

In this experiment, the graphite acts as a variable resistor (potentiometer). By changing the length of graphite through which electricity travels, you change its resistance, which controls how brightly the LED glows.

Real-Life Applications

Materials Required

  • 2B or 4B pencil (recommended)
  • 9V battery
  • LED
  • Connecting wires with alligator clips
  • 220–470 Ω resistor (recommended for LED protection)
  • Pocket knife or sandpaper
  • Sheet of paper

Step-by-Step Instructions

Step 1

Carefully remove a small strip of wood from the pencil to expose the graphite.

Amazing Pencil Resistor Science Project: Build Your Own Variable Resistor with a Pencil in 5 Steps

Step 2

Connect the positive (+) terminal of the battery to one end of the graphite using an alligator clip.

Step 3

For best results and LED safety, connect a 220–470 Ω resistor in series with the LED.

Connect the negative (–) terminal of the battery to the short leg (cathode) of the LED. Connect the resistor to the long leg (anode) of the LED.

Step 4

Connect a wire to the free end of the resistor (or directly to the LED if you are demonstrating only with graphite).

Amazing Pencil Resistor Science Project: Build Your Own Variable Resistor with a Pencil in 5 Steps

Step 5

Touch the free wire to the graphite close to the battery clip. The LED should light up.

Step 6

Slowly move the wire farther along the graphite and observe how the LED’s brightness changes.

Amazing Pencil Resistor Science Project: Build Your Own Variable Resistor with a Pencil in 5 Steps

The Science Behind the Activity

  • Graphite is a conductor of electricity.
  • Pencil “lead” is made from graphite mixed with clay.
  • Graphite allows electricity to flow, while clay increases its resistance.
  • The graphite inside the pencil acts as a variable resistor.
  • When the contact point is close to the battery clip, electricity travels through only a short length of graphite.
  • A shorter graphite path has lower resistance, so more current reaches the LED and it glows brightly.
  • As you move the contact farther away, electricity travels through a longer section of graphite.
  • A longer graphite path has higher resistance, so less current reaches the LED.
  • As a result, the LED becomes dimmer.
  • This demonstrates how changing resistance controls the flow of electric current.

Why Add an Extra Resistor?

Although the graphite limits the current, its resistance changes depending on the pencil grade, thickness, and length. Softer pencils (such as 2B or 4B) contain more graphite and usually have lower resistance, while harder pencils (such as HB or H) contain more clay and have higher resistance.

Because the graphite’s resistance is not always predictable, adding a 220–470 Ω resistor in series helps protect the LED from excessive current. This makes the experiment safer, more reliable, and scientifically accurate.

Pro Tips

  • Use a fresh battery for the best results.
  • Always check the LED polarity before connecting it.
  • 2B or 4B pencils usually work much better than HB or H pencils.
  • If the LED does not light up, make sure the graphite is exposed well and all connections are secure.
  • For classroom demonstrations, always use the recommended series resistor to protect the LED.

Expected Result

When the contact point is close to the battery clip, the LED glows brightly. As you move the contact farther along the graphite, the LED gradually becomes dimmer because electricity must travel through a longer section of graphite. The increased resistance reduces the current flowing through the circuit. If the graphite path becomes long enough, the LED may become very dim or stop glowing.

Conclusion

This simple pencil resistor experiment shows that an ordinary pencil can behave like an electronic component. The graphite inside the pencil acts as a variable resistor, allowing you to control the flow of electricity by changing the length of the graphite path. The same principle is used in dimmer switches, volume controls, and many electronic devices.

Adding a small 220–470 Ω resistor makes the experiment safer by protecting the LED while still allowing students to observe how graphite changes the resistance in the circuit. Through this activity, students discover that the basic science behind a simple pencil is the same science used inside modern electronic devices.