To show the existence of the potential and the shape of the potential distribution, a fluorescent bulb is brought near a Van de Graff electrostatic generator.

Directions: First, make sure the bulb is held with its long axis oriented along a radius. A potential difference between the ends of the bulb causes it to light. Now, turn the bulb 90 degrees so that each end is the same distance from the center of the sphere, the bulb will not light, indicating that the ends are at the same potential.

Suggestions for Presentation: Holding the fluorescent bulb in your hand is entirely safe, although you might occasionally get a spark. Hold one end about half a meter or so from the sphere. With the room lights dimmed, a highly visible glow should result. Then turn the bulb 90 degrees so that each end is at the same potential.