Van de Graaff generator with an electrical spark (centre) crossing from the generator's sphere (left) to a nearby metal object (right). A Van de Graaff generator works on electrostatic principles by using a moving belt to build up electrical charge on the metal sphere. When the electrical charge is high enough, a spark will be transmitted from the sphere, through the air, to nearby objects, as seen here. The Van de Graaff generator was developed by Robert J. Van de Graaff from 1929. Large Van de Graaff generators have been built that can generate voltages of millions of volts. Smaller models are used in classrooms, and other educational facilities, to demonstrate the principles of electrostatics.