Why are electric sparks blue?

11 September 2011

Question

Do electric sparks or arcs display blue hues due to Rayleighs scattering? Thanks,
Luka
Brisbane, Australia.

Answer

Dave - An electric spark is essentially electricity flowing through a gas and in doing that, it has to rip the electrons off the gas. Sometimes those electrons recombine with the atoms, at which point they release lots of energy in the form of light. Different gases release different colours of light. So argon produces a purply colour, helium often a reddy colour, sodium as a gas that produces a really bright orange colour, which you see from sodium street lights, and nitrogen, which makes up most of the air, glows with a blue colour. So, a spark essentially nitrogen glowing. Diana - Right, so if you set off a spark on Venus, you'd probably get quite a different colour. Dave - Yes. Venus's atmosphere is mostly carbon dioxide and I think carbon dioxide certainly can glow with a kind of yellowy greeny colour.

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