Tesla coil. Members of the Tesla Coil Builders Association seen with their largest coil, nicknamed 'Nemesis'. A Tesla coil is essentially a large air-core transformer with a capacitor, named after its inventor, physicist Nikola Tesla (1856-1943). The coil is designed to give a high- voltage, high- frequency spark. 'Nemesis' creates a spark sixty times per second using mains electricity, but at over 1 million volts. Photographed in Richmond, Virginia, USA.