Friday, December 26, 2014

electricity - Why do electric sparks appear blue/purple?



Electric sparks tend to appear blue or purple or white in color. Why?



Answer



Air is normally a bad conductor of electricity, but with enough voltage it can be converted to plasma, which is a good conductor. In a plasma, the electrons constantly bind to and leave atoms. Each time an electron binds to an atom, it emits the energy in light. As a result, the plasma glows the color of a photon with that energy. There are a few different energy levels that get involved, so the spectrum has a few different peaks. The final color depends on the gas you use. For example, neon looks red or red-orange. Air ends up looking blue, so electricity passing through air makes it glow blue.


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classical mechanics - Moment of a force about a given axis (Torque) - Scalar or vectorial?

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