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> Colours of electiricy
ddy
Posted: Jul 22 2006, 01:23 PM


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If i recall correctly a bolt of electricity like lightning is made of plasma, material made of electrons? Or somthing like that

Anyway, there was a lighning storm this morning at 4am and the bolts were green. This got me to wonder why some bolts of electricity are differnt colours. I have seen bolts of lightning that are yellowish white, blue and green.

When i play with my own electricity like the mains or 12v supply, i also get differnt colours like orange, blue and white.

Why does this happen?
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mr_homm
Posted: Jul 22 2006, 02:58 PM


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This is controlled by temperature. The hotter sparks will be blue and the cooler ones red. (Do a search for "Wien displacement law" to see a formula.) Basically, the product of temperature and wavelength is constant. Hotter spark --> shorter wavelength --> bluer light.

The temperature of the spark depends on a bunch of circumstances that are hard to predict. One lightning bolt migh be striking through drier air than another, or may be driven by a higher voltage than another, or probably many other variables that I haven't thought of. Your battery or power mains sparks temperature depend also on the humidity and on the distance the spark has to jump. Longer distance requires a higher voltage in order to for the spark force its way through the air, but the voltage actually produced depends on what is driving the spark. A spark from a capacitor has a constant voltage, so if it is shorter, all its energy will be dumped into a smaller volume, and so the spark will be hotter and bluer. On the other hand, a spark from an inductor will produce as much voltage as it needs to make the jump, so a longer spark will have a higher voltage, which will drain the inductor faster and produce a briefer, but not redder, spark.

Hope this helps!

--Stuart Anderson


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A hallmark of intelligence is the ability to give precise answers to vague questions.
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ddy
Posted: Jul 22 2006, 08:02 PM


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Temperature of the sparks... Got it!

So its actaully possible to have every colour in the visible spectrum of light then happy.gif .
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Zephir
Posted: Jul 22 2006, 08:31 PM


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QUOTE (ddy @ Jul 22 2006, 04:23 PM)
...why some bolts of electricity are different colors. I have seen bolts of lightning that are yellowish white, blue and green....

The violet lightning color is due the presence of red lines of hydrogen spectrum from water vapor, it means, the violet lightning are quite common in the rainy storms at low altitudes. The nitrogen spectrum is preferably blue (consider the color of nitrogen laser) instead, so such color is typical for the lightning in dry conditions. Low frequency bolts contains the orange to red component coming from Rydberg atoms, which gives the green to orange color to such lightning. Such color is typical for ball lightning.

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This post has been edited by Zephir on Jul 22 2006, 08:52 PM


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ddy
Posted: Jul 23 2006, 03:22 AM


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Wow...

Lots of good info thanks!
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