A Tesla coil is a type of resonant transformer circuit invented by Nikola Tesla around 1891. It is usually used to generate very high voltage, low current, high frequency alternating current electricity. A Tesla coil consists of two, or sometimes three, coupled resonant electric circuits, but is difficult to define precisely, as Tesla experimented with a large variety of coils and configurations. Tesla used these coils to conduct innovative experiments in electrical lighting, fluorescence, x-rays, high frequency alternating current phenomena, electrotherapy, and wireless power for electric power transmission.
Early Tesla coil designs usually employed a high voltage power source, one or more high voltage capacitor(s), and a spark gap to excite the primary side of the Tesla coil system with periodic bursts of high frequency current. Later and higher-power coil designs had the primary and secondary circuits tuned so they resonated at the same (high) frequency (typically, between 25 kHz and 2 MHz). These larger Tesla coil designs are used to create long electrical discharges.
Tesla coil circuits were used commercially in sparkgap radio transmitters for wireless telegraphy until the 1920s, and in electrotherapy and medical devices such as violet ray. Today their main use is entertainment and educational displays. Tesla coils are built by many high-voltage enthusiasts, research institutions, science museums and independent experimenters. Modified Tesla coils are widely used as igniters for high power gas discharge lamps, common examples being the mercury vapor and sodium types used for street lighting. Although electronic igniters are available, Tesla's original spark gap design is much cheaper and has proven extremely reliable.
Contributed by Nitin Sinha
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