PURPOSE: To demonstrate Jacob's ladder.

DESCRIPTION: The spark starts at the bottom of the ladder, where the small spacing encourages electrical breakdown. The discharge heats the air, which begins to rise. Because the discharge is a region of least electrical resistance, the spark continues along that path, which continues to rise. At the top of the ladder the discharge path becomes so long that its resistance is greater than the resistance of the shorter path at the bottom of the ladder. At that point the discharge ceases and starts again from the bottom.

SUGGESTIONS:

EQUIPMENT: Jacob's ladder demo.

SETUP TIME: 30 min.