The Tesla Coil, created by Nikola Tesla around 1890, is a resonant transformer, which is used to produce high-voltage in a high frequency.

There are many ways to build a Tesla coil. This equipment requires two basic circuits and it is usually composed of an air-core transformer, a primary capacitor, a spark gap, a primary coil and a secondary coil.

The Tesla Coil works in the following way: the transformer charges the capacitor and increases the mains voltage, which is transferred to a spark gap that discharge on primary coil. This coil is assempled near to the bottom of the secondary coil connected to ground. Gradually, the energy that is oscillating with low voltage and high current in the primary coil is transferred to the second coil, which has high-current oscillation and high voltage. When the energy dies out in primary circuit, its oscillation, that is only in the second circuit, feeds sparks and high-frequency corona. This combination of high-frequency and high-voltage can generate an electric field, able to ionize the air and to spread as sparks.

It is posible to build the coil circuit at home with some materials, but you much be careful. A Tesla Bobine raises electric currents to very high values, between 250 kA and 2 MA, and “touching” on a lightning directly can be lethal or cause third-degree burns. But anyone can hold and bring closer a metal baton to attract sparks or even a lamp, which will turn on when feed by this energy.