Tinker: Graphite Lightbulb

by STEM Scouts


  • 8 D Batteries
  • 0.7mm Pencil Lead
  • Electrical Tape
  • Mason Jar
  • Small Cup
  • 2 Wires with Alligator Clips
  • Safety Goggles


  1. An adult is advised to conduct steps 6 and 7 of the experiment. On that note, begin by putting on your safety goggles.
  2. Lay the D batteries end-to-end, positive to negative, and tape them together.
  3. Tape one end of one alligator clip to the negative end of the battery chain. Then tape the other clip to an upside down small cup with a with the clip extending from the bottom of the cup. Grab the second wire and tape one end on the opposite side of the upside down cup. Note: If you do not have a cup you can use an empty toilet paper roll.
  4. Grab a piece of pencil lead and set it in place using the two alligator clips attached to the cup.
  5. Place the mouth of your mason jar over the pencil lead, clips, and base of the upside down cup.
  6. Take the free clip from the second wire and connect it to the positive side of the battery chain. This completes your circuit.
  7. After a moment the graphite should begin to produce smoke and glow brightly.
  • You’ve now built your own light bulb! What do you think will happen if you try different weights of pencil lead—0.5mm, 0.9mm, or even lead from a wood pencil?
  • How can you tweak the setup to get the pencil lead to glow for a longer time? Consider altering these: the length and weight of the pencil lead, the position of the alligator clips on the pencil lead, whether the mason jar covers the cup or not, and more or fewer batteries.

How Does It Work?
This experiment is a visually exciting introduction to circuits and electricity. When you attach the final alligator clip to the positive end of the battery chain, you create a complete circuit, and that allows electricity to flow through it. As electricity travels through the pencil lead, which is actually graphite, it heats it up to an extremely high temperature causing it to glow and emit smoke.

This works similarly to the filament in a common light bulb. Filaments in light bulbs are made of tungsten because it can produce a lot of visible light and has a high melting temperature. It is, however, also prone to combustion, much like our smoking graphite, which explains why your household light bulb differs in the manufacturing process: the bulb is vacuum-sealed to get rid of oxygen, one of the necessary components of combustion.




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