What is a Tesla coil?

Question

Why is it for?

Answer 1

It's a type of transformer, used to generate high-voltage, alternating-current electricity.  Nikola Tesla used them to conduct experiments in lighting, fluorescence, and wireless power transmission.

They were used in the first wireless radio transmitters, but today they're largely used in museum demonstrations to educate people about electricity (and they look cool in mad scientist movies...)

Answer 2

Small hand-held Tesla coils are still quite commonly used to test the integrity of high voltage insulation in the power industry.

Answer 3

A Tesla coil is a category of resonant transformer invented by Serbian-American scientist Nikola Tesla around 1891.[1] It is generally 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. A Tesla coil is difficult to define, as Nikola 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, electro therapy, and wireless power for electric power transmission.