i have a quesion .
simple one .
as i understood it while back . that there is no such a thing 100% insulator .only materials with huge resistance

am I getting this right ?

wood is insulator . but if a lightning hits it , it becomes a conductor, right?


bye
thanks
eko
Posted on 2003-04-24 11:48:20 by eko

i have a quesion .
simple one .
as i understood it while back . that there is no such a thing 100% insulator .only materials with huge resistance

am I getting this right ?

wood is insulator . but if a lightning hits it , it becomes a conductor, right?


bye
thanks
eko


Wood contains moisture so if there is enough potential applied to it (as in lightening ) it will conduct and explode. (Actually in this case it does not have enough resistance so the current goes through the roof and super heats the moisture into vapour)

The only perfect resistor material would be a vacume and even then strong charges can jump the gap as in the operation of old tv tubes. Thats why tv tubes run on such high voltages.

The strongest resistor materials to electron flow are those that have filled valence shells in their electron orbits because they don't want to give or take an electron. Their outer shell is already complete.

I'm not sure what the materials are with the highest resistance but in practical applications resistors materials themselves have to conduct..just not very well such as in carbon resistors.



Just my ramblings.
Posted on 2003-04-24 13:09:33 by IwasTitan
IwasTitan has a good point, even a pure vacumn can conduct under the right conditions, but no one would mistake it for a 'material.'

I've never did any study of materials for insulation properties. Just a nuts and bolts engineer here, do my research in a catalog of things people supply. If I need an insulated wire, I buy it like that.

I could imagine some 'material' that could impead ions from passing thru, thus being a better insulator then vacumn itself, but thats a guess.

eko, is there something that prompts the question, or is it just theoretical? Thats not a put-down, I love theoretical questions too. I'm just trying to see where the question springs from.
Posted on 2003-04-24 19:26:50 by Ernie
even a pure vacumn can conduct under the right conditions
But if there is nothing there does any electron conduct it? Hmmm. It can't travel with moisture in the air so can it jump the gap in a pure vacuum?

eko, you are right. Think of a tree in the woods that gets hit by lightning. The lightning is attracted to the earth's potential and conducts itself through the tree, finding the path of least resistance. The flow through the tree may be more due to its moisture content than the wood itself.
Posted on 2003-04-24 20:57:15 by drhowarddrfine
I would speculate that you can get better insulators than a vacuum.

After all a vacuum has no impedace to moving electrons. Only electromagnetic fields and gravity effect a traveling electron in a vacuum. To me this is low friction. You just have to force them off the conductor first (via electromagnet forces).

A true insulator is like running the 100m dash ontop of a junkyard. You bounce into EVERYTHING along the way. To the point where the toll is to high of a price to pass electrons though at a significant rate. It true there will always be electrons making it through. But remember that you need 6.24*10^18 electrons before you even have a coulomb. And to make them get through within a second is an Amp.

It takes approximately 50mA to kill someone (under idea conditions). So to have even 50uA implies you need 50/1000000 Amps, or 0.00005 Coulombs/Second. This is approximately 3*10^14 electrons / second. Its still alot! I would speculate things like ceramics would offer far more resistance to current flow than a vacuum....

:NaN:
Posted on 2003-04-24 21:18:09 by NaN
Yes, there is no such thing a perfect insulator. At the same time there is no such thing a perfect conductor.

The ability of any material to conduct is revealed by looking at the materials atomic structure. Electrons rotate around the nucleus. The electrons are grouped into shells. These shells are arranged into groups that correspond to fixed energy levels. The shells are populated with electrons using a forumla called Pauli's exclusion principle or simply 2(n*n), where n is number of the shell beginning with the shell closest to the nucleus. So the first shell can have a maximum of 2 electrons, the 2nd shell a maximum of 8 electrons and so on. A materials conductive qualities is determined by it's outermost shell or Valence Shell. An atom's valence is it's ability to gain or lose electrons. The valence electrons are the key to electricity. They are the electrons that are easiest to break loose from the parent atom.

Normally conductors have 3 or less valence electrons, semiconductors have 4 valence electrons and insulators have 5 or more valence electrons.
Posted on 2003-04-25 14:29:08 by alpha
The valence model does not take into account ionization.

Dissolve salt in water, and you get Na+ and Cl- ions, which makes salt water a BETTER conductor than plain water. The Na+ and Cl- ions have filled outermost shells.

Neon ionizes at about 70V. Neon is a noble gas, containing a full shell of outer electrons. Ionized neon conducts. (I don't know the characteristics of ionized neon.) Ionization works with other noble gases: krypton, argon, xenon.
Posted on 2003-04-25 15:34:11 by tenkey
All gasses will ionize, the reason neon is so usefull is an ion is usually highly chemically reactive, but using a nobel gas means it ain't gonna react anyway no matter how many electrons you strip away.
Posted on 2003-04-25 17:51:07 by Ernie
Given enough energy, the noble gases will combine. Oxides of xenon and krypton have been created. IIRC, a highly charged environment is required, similar to creating ozone (O3).

There's probably a difference between gaseous ionization, obtained by adding energy, and solution ionization, where the ion particles are probably in a lower energy state than in the undissolved molecule. Or is this bad physics/chemistry?
Posted on 2003-04-25 21:22:33 by tenkey
You've got me there tenkey. I must admit though, I've never seen any electronic conductors made of liquids or gases. I can also assert that in most solids the transfer of charges is by the movement of electrons rather than ions.
Posted on 2003-04-25 21:36:30 by alpha
Two fundamental properties of insulating materials are insulation resistance and dielectric strength.

Insulation resistance is the resistance to current leakage through the insulation materials.

Dielectric strength is the ability of an insulator to withstand potential difference. It is usually expressed in terms of the voltage at which the insulation fails because of the electrostatic stress.
Posted on 2003-04-25 22:25:40 by alpha
Any 'wet' cell battery, such as the lead/acid battery in every car I've seen, has a liquid as a conductor.

Offhand I can't come up with a common gaseous state conductor. Any takers?
Posted on 2003-04-25 22:25:55 by Ernie
We can play gotcha all day. I would not prefer that sort of dialog. It seems the net is full of this type behavior.

My posts were in context to the original question. Should electronics newbies be led to believe that valence shells are not valid? Or is this going to spin off into a chemistry semantics course?
Posted on 2003-04-26 00:28:01 by alpha
The KISS response. There are only insulators that are "Good Enough" and others that aren't.

Some insulators act like resistors (conducting more at higher potentials) while others are more like capacitors (conducting (leaking) almost nothing until the break down voltage; then turning into a very good conductor).

Pure water is a good insultator (with a dielectric constant of 78 compared to a vacuum with a dielectric constant of 1.000). However pure H20 is pretty rare. Water usally contains a lot of ions, dissolved minerals, etc.
Posted on 2003-04-26 02:09:55 by eet_1024
alpha,

Actually they are interested in spinning off into the physics and chemistry of this.
Posted on 2003-04-26 10:10:02 by drhowarddrfine
Hay Iv'e forced galss to conduct with heat and 20,000 volts
it won't do it for long befor it shatters

the way to do it is to wrap an arc around the edge of a peace of glass
let the arc heat up the glass and at some point the arc will pass through
the galss giveing off white light as dose and in a short time the glass will shatter
Posted on 2003-04-26 20:14:07 by rob.rice

Any 'wet' cell battery, such as the lead/acid battery in every car I've seen, has a liquid as a conductor.

Offhand I can't come up with a common gaseous state conductor. Any takers?


Take a water molecule and split into oxygen and hydrogen.

Put both gases in a balloon and nothing happens. However if you place a piece of platinum in the balloon it will explode.

The platinum acts as a switch to cause electron exchange. A catalyst.
Posted on 2003-04-26 23:02:12 by IwasTitan

My posts were in context to the original question. Should electronics newbies be led to believe that valence shells are not valid? Or is this going to spin off into a chemistry semantics course?
I'm willing to allow mentioning valence electrons up to a point. But classifying conductivity by valence count leaves a fair portion of electronics unexplained. I didn't realize how much wrong it was. When I went to look at a periodic table...
Posted on 2003-04-27 03:15:36 by tenkey
Looking at the original question tenkey, ionization comes into play when you examine the lightning. That electromotive force, such as a battery, conducts but is not defined a conductor in solid state electronics. It's commonly called a voltage source. Valence electrons apply in solids and it really works. What we're really discussing is apples and oranges from the same orchard.
Posted on 2003-04-30 11:16:27 by alpha
Any light emitting lamp of gasous nature, most common is the fluorescence light bulb. We mainly use it for it's by-product, that is light.

Regards, P1
Posted on 2003-04-30 12:23:35 by Pone