I was wondering why electrical arcs are blue. I WAG it is the moelcules of the air being excited by a current passing through them (due to dielectric breakdown). In short, you’re not really seeing electricity, but rather its effect? …or, am I splitting hairs?
Dunno. Could it have to do w/ the ionization of air?
Yes, it’s due to the ionization of the air, and the color depends on the atoms involved. Air ionizes blue-white. Sodium ionizes yellowish. IIRC, helium ionizes red. An electric arc in a vacuum is invisible (as can be seen from any working vacuum tube - the only glow is coming from the heater coil).
abit of highjack but i need to clear this ignorance of my…
How does an electric arc happen in vacuum?
An “electric arc” in vacuum is just an electron beam. It can happen if you generate electrons and let it flow along an electric field, or just accelerate the electrons and shoot it into vacuum.
Partial (imperfect) vacuum is the easiest environment in which to produce an arc. There are lots of atoms floating around, so these get ionized and carry current. But there aren’t too many molecules so the charged atoms and electrons can flow easily without bumping into many atoms. If you improve the vacuum, there are fewer atoms to carry current so it becomes harder to produce an arc. If you increase the pressure, motion of the charged particles will be affected so it becomes harder to produce an arc. So if you want to use a few thousand volts in a vacuum chamber, for instance, you have to pump down to about 10^-6 torr to prevent accidental arcs.