Jacob’s Ladder

Figure 1

Figure 1: Jacob’s ladder arc

This demo shows an electric arc that rises between two vertical conducting bars separated wider at the top. Once the arc reaches the top of the “ladder” and vanishes, another is generated at the bottom to repeat the cycle.

 

 

 

 

Materials:

  • Jacob’s Ladder – High voltage power supply connected to two conducting bars close together at the bottom and farther apart at the top (Figure 1)
  • Foot switch
  • Surge Protector (recommended)
  • Extension Cord

Demo:

Firstly, place the demo in a position clear from any flammable or combustible materials. Then plug in the power cord to the foot switch, and foot switch into a grounded outlet. If using a surge protector, use the switch on it to power it on. Use the foot switch to provide power to the Jacob’s ladder. The arc will immediately form and rise up the bars until it vanishes and another arc forms. Hold a piece of paper to the arc to light it on fire.

Explanation:

When the power supply is turned on, the initial high voltage ionizes the air in an arc between the two rods where they are closest, and consequently where the electric field is largest. The arc then heats the air around it. As hot air begins to rise, it brings the arc with it until the conducting bars are separated too much for the voltage to keep the arc withstanding (Figure 1)

When the arc forms, the potential between the rods drops because of the subsequent current flow. For an alternating current:

V = IZ

Where I is the current and V is the voltage. We can see by this equation that the impedance and voltage are proportional, so as impedance increases or decreases, voltage does the same. As the arc rises, the impedance increases, causing the voltage between the bars to increase. Once the arc vanishes, the voltage returns to its original open circuit voltage, sparks a new arc, and repeats the process.

Notes:

  • This demo uses extremely high voltage, only demo room professionals should operate it.
    • The transformer at the base of this apparatus generates 15,000 V.
    • Use proper PPE including electrical gloves and insulating floor mat
  • Use the foot switch to turn on the device.
  • Never move or lift the apparatus by the insulators. Only use the handles attached to the base.
  • Must be connected to a grounded outlet or surge protector.

Written by Lydia Seymour
Updated by Phoenix Gallagher