This is the most important device behind the VandeGraaff Generator. If I can relate this well enogh the rest of the device should be easy enough to understand. The sphere collects the charges that the generator carries into it with the rubber belt. The functionality as a storage device is very important becuase over time the sphere gains a higher and higher potential until the environmental aspects as well as the spheres own physical limitations keep it from gaining any higher of a voltage. The way that the sphere manages to continue with charging until external effects stop it is through the faraday cage effect. In this effect electrons which pass into a container always travel to the outside meaning that as the electrons are carried in by the belt the sphere does not resis the movement of electrons and instead accepts them into the sphere to be passed to the outside of the device.
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Ground in this case is an external ground through which electrons and protons travel to and from the belt what this means is that the belt when charging can use the belt either to gain or to loose electrons. Also this ground is the relative voltage of 0volts to the the charging sphere meaning that between these two points exists an electrical potential and between the points is where that potential would be measured. Return to the Diagram
The motor must simply be good enough to transport the belt around and do it in a fashionable speed to deliver electrons to the sphere. Return to the Diagram
The bottom needles act to strip away charges of the opposite sign of the spherical terminal they also help in the self excitation process of the belt. Return to the Diagram
The top needles are very important in that they work to remove the electrons from the belt and transfer them to the sphere where they are collected and add to the total potential of the device. The needle design is very important too many or too few can lead to poor preformance of the device. Return to the Diagram
The Spherical terminal is insulated from the grounding terminal through the air as well as through the material supporting it (in most cases this is a peice of PVC). The amount of maximum potential charge is limited by these two insulators. If the air is most it has a higher tendency to accept electrons, and unfortunaely for the PVC it is hydroscopic meaning that it absorbs water ever so slightly but the moisture derades its insulative value. Therefore in a dry atmosphere is the best place to acheive the best performance. If this is not a practical solution the next bes thing is man made drying. Several things can acheive this, de-humidifier, hairdryer, light bulb (to heat the unit thus dissipating moisture) and de-humidified chemicals. The only item listed here that will actually change the environment is the de-humidifier which is effective in removing moisture from the air thus increasing potential for the sphere. The other methods help the device itself gain a high potential limited only by the air. Return to the Diagram
The upper pulley is important in the self excitation process whatever it is it must be the opposite insulative value of the bottom pulley. In this case a metal conductor is the opposite of the insulator. Return to the Diagram
The belt and its material is extremley important. Without the proper material (usually rubber) the self excitation process cannot be enacted and electrons will not be seperated meaning that it will have nothing to transfer to the sphere. In this case since the belt is of the proper material it adds to the speed with which electrons are delivered and increases the current. Say that the belt width were to be increased. This has the effect of increasing current flow becuase the speed with which electrons are transfered increases. The one thing that does not overwhelmingly influence design is the belt length. No matter how long a belt it is always limited in how many electrons it can carry (not to deny that increasing belt lenght increases potential because the device is farther from anything that it could potentially leak through). Return to the Diagram
