5D40.10 Jacob's Ladder


Conduction in gases


Two long metal rods are connected to a step-up transformer. When the power is turned on, a voltage is created between the two rods that exceeds the dielectric breakdown of air. As a result, a spark forms across the rods where they are nearest to each other. As the heated ionized air rises, the spark appears to move upward until the trail of ionization breaks since it becomes less stable as it grows longer.



  • [1] Step-up transformer connected to metal rods
  • [1] Clear plastic tube

Safety Equipment

  • [2] Safety glove

Important Notes

  • Lethal voltage is used in this experiment. Wear safety gloves when handling the apparatus.
  • Please unplug the transformer after you are finished.


  1. Put on your safety gloves.
  2. Place the plastic tube to cover the exposed metal rods.
  3. Connect the transformer to a power source.
  4. Turn on the transformer.
  5. When finished, turn off the transformer.


Additional Resources


  • PIRA 5D40.10


  • Don't attempt this at home!

Last revised

  • 2020


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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.