An Oudin coil can take the energy out of your outlet and create sparks you can see! It’s sometimes called a mini tesla coil. The sparks on them usually look violet.
Oudin Coil spark
If you know the visible light spectrum, you might know that violet light is the most energetic color of light. 
Oudin Coil light
The oudin coil looks like it’s putting out a lot of energy, but there’s a different reason for the violet sparks. In fact, the color of the sparks don’t always have to be violet like most people see. To demonstrate, check out the oudin coil when it sparks in something else, like carbon dioxide. An easy way to get a bunch of carbon dioxide in one place is with its solid form — dry ice!
Ice
When surrounded by CO2, the sparks from this oudin coil are clearly a different color!
Oudin Coil ice sparks
The reason for the color shift is because of what is surrounding the oudin coil. Our air is less than 1% carbon dioxide. When sparking in air, the coil surrounded mostly by different gases (mainly nitrogen and oxygen). The answer to why that makes a difference is the same answer as to why different gases glow different colors when you put a lot of energy into them. 

light colors
If you split apart this light, with something like diffraction glasses, you’ll see each type of gas has a unique spectrum of light. The study and use of this phenomenon is called spectroscopy.

Spectroscopy is a way of identifying gases, and it’s how we know what far away things like stars are made out of! On a tiny molecular scale, CO2 and what makes up our air are fundamentally different, and will create differences we can see… if we are clever enough to notice. By playing with this oudin coil and looking at colors, we’re revealing secrets about a seemingly invisible world.
Written By: Amanda Williams

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