This demonstration device is used with a Van de Graaff generator to show that like charges repel and there is noticeable force involved in the repulsion.
The unit should be mounted on top of the N-140 Insulating stand (as shown). The ring should then be connected to the dome with a short piece of insulated wire (not included). The N-126 Terminal with suction cup will be of great help in making this connection. Another wire jumper should connect the small hook arm on the insulated stand to the ground post on the Van de Graaff generator. When the generator is running, the ball will roll around the periphery of the dish.
The disk above the ball is of course, at high potential since it is directly connected to the dome. Some electrons will “escape” from the disc to the closest surface of the ball. The electrons on the ball are sitting on an insulator and are, not free to move around. Since they can’t move, a repulsive force is immediately established between the upper disk and the ball, with the natural result that the ball rolls and a new surface is available to receive more electrons. When the charge carried on the rolling ball reaches the lower pan, it is drained off to ground. As the ball turns,one side is carrying charge down to ground and the other side is moving up toward the disk for a new charge. This helps to understand why it is sometimes helpful to jiggle the ball just a touch to get it started.
Dish diameter: 14 cm