There's
something mesmerising about electric arcs and lightning. I've always
found them fascinating. The dielectric strength of air is 3000 volts per
mm, meaning it takes 3kV for a spark to jump a distance of one mm
between rounded electrodes, less if there are sharp edges. Between the
electrodes, a plasma is formed, the fourth state of matter (the other
three being solid, liquid and gas). The temperature of an electric arc
can be 5000 degrees C or more, hotter than the surface of the Sun, the
arc generating intense short wavelength UV radiation, light and heat
(and can cause sunburn when arc welding, if PPE isn't used). Arcs also
generate radio waves and spark transmitters were used in the early part
of the 20th century for transatlantic and ship to shore communication.
Information was sent by Morse Code, and although telephones had been in
use since the end of the 19th century, it would be several more years
before the transmission of voice using radio waves became possible and
commonplace.
