Giant Van de Graaff Generator at Maker Faire

While this isn't exactly clean technology it's definitely worth sharing! This year at the Maker Faire in Silicon Valley there was a 10 foot tall Van de Graaff Generator that had the crowd going wild. A Van de Graaff generator demonstrates a number of principles including the relationship between charge and voltage, Q = CV, where C is the capacitance of the dome. The capacitance of a sphere with respect to infinity is about 1.1 pF per centimeter of radius. The electrical energy stored in the Van de Graaff generator is CV2/2. Energies below about 10 joules (corresponding to a dome with a 27-cm radius) are relatively safe... the one at Maker Faire would probably kill you.

Attendees were required to stand 15 feet away from this Van de Graaf but had it been smaller, and users a bit closer, their hair would have been standing up on end! This is because hair acquires charges of like sign which tend to repel one another. The Van de Graaff generator was one of the earliest particle accelerators used for nuclear physics research. Modern Van de Graaff generators and other similar electrostatic accelerators are still used for that purpose and are capable of voltages in excess of 20 million volts.

One of the interesting things about experiencing this demonstration in person was the smell of Ozone in the air. The Van de Graaff breaks apart Oxygen as it electrofies the air. Splitting dioxygen or O2 allows three Oxygen molecules to bond together and that resulting O3 is called Ozone. This same sort of smell occurs when you use an ionic breeze. Too much Ozone isn't good for you to breathe and it also oxidizes metals but the doors were open and fresh air was flowing at Maker Faire so I don't think anyone was hurt ;)

More about air purifiers and how they work here and Van De Graff generators here. Below is a great video by CNN interviewing Mister Jalopy, a man who supports the maker movement.