Concepts

Conduction in gases

Overview

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.

Details

Equipment

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

Classroom Assembly

1. With the apparatus unplugged, place it in a visible spot for students.
2. Place the plastic tube around the exposed metal rods.
3. Plug in the apparatus.
   

Important Notes

• Lethal voltage is used in this experiment. Do not operate the demonstration without the plastic tube around the electrodes.
  
• Please unplug the transformer after you are finished.

Script

1. Turn on the transformer.
2. When finished, turn off the transformer and unplug it.

Additional Resources