Why does electricity cause sparks?

Hi everyone!

Why does electricity cause sparks? I have two scenarios in my mind, and i hope someone can provide me good answers.

1) I have seen on a lot of occasions, for instance the main transformers near my home, the wires sometimes keep sparking near the area where the wires are joined to it. Why does it spark? What is actually happening? And i do know that it might be caused by an overload or a short-circuit or stuff, i am not talking about what caused the sparking, but what is happening when one occurs. Why not just burst into flames, or heat red hot like a metal filament or something?

2) I have also observed sparks when, lets say i suddenly pull out the plug from the socket with the switch still ON, or sometimes even when i turn ON/OFF a switch driving a load. Why does this occur? 

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Yes, you've got it exactly right. There, as always, complications that make the real world more sophisticated (look up "gas discharge tubes" to see just how complex things can be).
charmquark (author)  kelseymh4 years ago
Hmm ok :)
kelseymh4 years ago
Your original question kind of got sidetracked into a discussion of how to do your own research. Wikipedia is a very good place to start with simple science questions like this one (the people writing and editing the basic science tend to be grad students in the field, not wackos with axes to grind).

For this question, the sparks have nothing to do with combustion. The spark is a simple effect of ionization: the breakdown voltage is the field required to ionize nearby atoms; for air, the breakdown field is something like 12 kV. When the free electrons recombine, they emit light, mostly in the low UV, violet, and blue part of the spectrum.

Voltage creates an electric field, and the strength of the field scales with the curvature of the surface. Near a sharp point (like the end of wire), the surface has a very high curvature, so you get a very strong electric field, and consequently a small region of very high voltage (110 VAC at a 0.1 mm tip corresponds to a local field strength of 1.1 MV/m).

A high field can ionize the nearby atmosphere, the ion/electron separation can then propagate that high local field, leading to a cascade discharge over to the other side (ground) of the voltage difference.

Now, going back to the color of the sparks. The blue/violet spectrum does correspond to a fairly high effective temperature. If the sparking goes on continuously, that temperature can build up enough heat for nearby materials to catch fire. Also, breakdown through a solid (like the edge of a plastic electrical plug) can lead to resistive heating of the material.
charmquark (author)  kelseymh4 years ago
Hmm yes, right you are! I am doing my own research now, although i started out pretty late :). Wow, thanks for the explanation! Oh, so that explains it. I was wondering why they put small tips and not plates tip generate arcs. So even though we are actually applying a relatively small voltage of 110V, the small area of the tip leads to a pretty strong electric field. And that leads to dielectric breakdown. I hope i got everything right there!
As always, thanks for the simple explanation Dr. Kelsey!
You're an undergraduate in electronic engineering. You will have access to the university library, and you're asking really basic electrical questions.....
charmquark (author)  steveastrouk4 years ago
See that is the problem. The thing is that our education basically SUCKS. We are never taught anything practically noting, and our basics practically suck. All they are interested are in marks and percentage. When you ask such questions in our college, you are NEVER given proper answer as the lecturer is only interested in our syllabus. I understand i might look like a complete idiot asking such silly basic questions, but trust me, you have not seen anything. See most of the students around here and you will understand what pathetic really means. All i ask is some patience in dealing with me as i am trying to come out of the box, break free of our pathetic system and trying to gain some knowledge. Thank you :)
You'd be as well signing up for one of MIT's EdEx courses. They light years better than the crud you're getting now. I really don't understand why Indian education has evolved the way it has, you have some of the best mathematicians and engineers on the planet, where the heck were they educated ?
charmquark (author)  steveastrouk4 years ago
Also, the "By heart" system is encouraged right from schools, to high schools, right into college where they keep following the same system(Exempting really good ones). Hence, if you try to ask them something out of book, heck even in the syllabus, which is not in the textbook, they won't know at-least 90% of the time. There are a LOT of factors apart from these contributing to the overall result of what you see now: Mostly bad colleges, real good ones are few and far by, expensive and way lot of competition, bad faculty, bad mentality and so on. The universities around the world like MIT's are WAY WAY.....(*Light years) ahead of us.
Now, real intelligent people may be the result individual brilliance, and not good environment maybe. Hard to say.
charmquark (author)  steveastrouk4 years ago
I think it is due to the local mentality of Past generation Indian parents: They follow the equation that More marks=more knowledge=great job=big salary=Better life. They are least bothered what you actually LEARN. They are more concerned about marks and grades. They think it will always lead to good jobs. So the people around here started "Learning by heart" to cope up with these demands. Almost all the top graders are such.
charmquark (author)  steveastrouk4 years ago
And talking about library, we technically have do a library, but with pretty much useless books. My only source of updated and fast information is the internet, which i had no access to until two years back.
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