Van de Graaff generator
The Van de Graaff generator was conceived by Prof. Robert J. Van de Graaff in the 1920's as a practical way to obtain very high voltages of electricity for the study of atomic physics, specifically to run particle accelerators.
This electrostatic machine has an unmistakable appearence to say the least. It is always comprised of a hollow metal sphere on top of an insulating support column. This particular style of electrostatic generator uses a moving belt to separate, collect and harness positive and negative charges. Van de Graaff generators are amongst the largest and most powerful static machines ever built due to their simplicity; a long flat belt driven by two pulleys.
How it works
- The Van de Graaff generator is made up of five essential components: Two rollers or pulleys, a belt made of an insulator, a rotating power source, two brush assemblies at either end of the belt and a large hollow storage/discharge terminal which covers the top roller and brush.
- The rotational power source is almost always connected to the lower pulley for practical engineering reasons.
- Once turning, the lower roller attracts negative charges while the belt builds a positive charge. The imbalance occurs because the two rollers are made from materials that naturally have opposite charges. As the belt moves, a positive charge in most cases is transported via the insulating belt; rubber in the case of smaller machines and paper in Prof. Van de Graaff's first large scale research versions.
- During rotation, the charge on the lower roller differs from the charge on the belt. This leads to the repulsion of electrons near the tip of the lower brush assembly and divests nearby molecules of the electrons. Free electrons, thus build in the air, hence get attracted to the positively charged belt.
- Once The positively charged belt attracts electrons in the brush and charges the collection sphere sufficiently, the air breaks in the form of an electric discharge and the positive atomic nuclei get attracted to the brush (positively charged) while the free electrons move to the belt. This is the point where objects get charged as they carry the excess charges from this point making it neutral. The The entire process repeats until another discharge occurs.