If two conductors are merely touched together electricity can flow between them. That just seems too easy somehow. I mean, just touching? That's ridiculous. I've always thought that it ought to need more intimate bonding between conductors for current to flow. Even if the conductors aren't touching, sometimes there's a spark.
Another question. Why do I wonder about such things?
Bill
I guess touch points are a singularity, but while they represent a small diameter they also represent a very short one too.
R = p(resistivity) x A / L
As L tend towards being infinitely short then the resistance from touching conductors is minimal.
Nothing wrong with trying to understand things that aren't immediately obvious.
BICBW
In metals there are usually an abundance of free electrons - these are very easy to separate from the atom which they orbit, and move to another one close by. Hence any conductive atom in close proximity can share its electrons, and allow a current to flow.
Air is an insulator, but it has a breakdown voltage (aka "dielectric strength") where given enough voltage or "electrical field strength" you can rip electrons from the atoms, even though they are not usually "free". The insulator is then said to have become "ionised" and will become conductive at least while the material remains ionised.
The point at which this happens is an intrinsic property of the material, but it's also a function of distance distance. For air you need a voltage difference of around 3kV/mm to cause a breakdown. o to get a spark to jump a metre you need a megavolt, but only 300V for a tenth of a mm and so on.
Because you are a bright spark ?
It is all part of the rich pageantry of life.
Only if there is a potential difference over the junction. Two disimilar metals can cause a current (electron) flow depending on the temperature at the join.
What do you mean by "merely touched"?
Once there is any contact force, there is a contact area and assuming the metals are clean, a constriction resistance (which you can look up for yourself).
Actually if you bring two copper wires close enough then Van der Waals forces will cause them to be attracted together so if they are flexible enough they will end up in contact.
And even if they are not touching, put a potential drop across them and even if the dielectric strength of the air is not exceeded, there will be some quantum tunnelling.
There are very few stupid questions.
Newsgroup alt.twaddle.twaddle beckons. Go for it!
Thanks John. A good answer.
Bill
Do you mean the phantasmagoria?
Bill
F*ck off Rod.
Bill
It was if you gloss over the bit where I left out the "three" in front of megavolt :-)
Weren't you assuming a humid atmosphere and sharpish points for the two conductors? :-)
"ridiculous"? You were once the aerial expert, but now you've sunk to nutter status in my eyes. By all means wonder, but please research before posting here.
Because you are inquisitive. There is of course an electrostatic field around a conductor and the air is not really a great insulator and can break down and the two different potentials want to be connected. I see no real quandary. However Superconductors are a different thing altogether. They somehow can join together in such a way that resistance is just not there at all, so unless you take energy ot of a system by magnetic loads etc, if you connect the wire into a loop current will flow all the time until the leakage reduces the voltage. However its not terribly efficient as the power to keep it cold enough is quite great. I do not see how you can have a superconductor at much above absolute zero, ie the temperature where any attempt to cool it cannot happen as there is nothing colder. I'd imagine that the Brownian motion in materials at room temperatures is where resistance comes from, since otherwise you would not get noise in valves and transistors. Brian
Oh, dear, and I avoided that pun deliberately. I used to play with transformers and transistor multivibrators when I was in my teens and was quite surprised just how easy it was to break down air to make some nice sparks off of, for example an old speaker transformer wired backwards, a few diodes and capacitors in a ladder and 1 capacitor across the lot. Even with no actual spark it fizzed away quite well.
The smell was nice but I'm now told ozone is bad for you, sulk. Brian
And what about static electricity, an issue I've had issues from lately as may here know. It is after all the basis of vander graph generators and windshurst machines, both of which I've built with varying success. Obviously its those ion imbalances again, but why should friction be the catalyst? We have all had vinyl records charge up merely by the stylus move through the groove, indeed on one cartridge it actually tended to flash over tto a screw at times from the record, or when cassettes are run very fast there are sparks from the hub to the metal spindle of that hub. Brian
A mere bagatelle sir.
Bill
Well that's going nowhere.
Bill
If only I could.
Bill
Clearly you have a very shuttered mind.
Bill
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