I would like to know why some material conduct electricity and some do not. For example wood does not conduct electricity. Why Not?
I know it has to do with NUTRON & PROTONS but can not figure out/remember?

Edward

Edward, It has more to do with the ELECTRONS than the others. The number of electrons on the outer shell of the atom known as the Valance Shell determines how conductive a material is. The fewer electrons the more conductive. The more electrons the more insulating. When electricity moves through an atom it pushes one of the electrons off of the valance shell and onto the valance shell of the next atom. It hits the electrons on that atom and moves them and the force pushes one off to the next, and so on.

Think of them desk things that have 5 hanging balls - when the first one hits the last one moves. If there were more balls there, the last one would move less. If there were less balls the last one would move farther.

Conductive materials usually have 3-4 electrons on the valance shell. Semi-conductors have 5-6. and Insulators usually have 7 or more.

Janet Cooper

Ahhh, the Theory(s) of Conduction... so many ways to explain it, so many ways to view it.

Off the top, in reality almost everything is Conductive. Sounds wierd? just wait to hear this next one!

The one and only "True Insulator" is... Water!
Alright, not all the facts are here, but I just wanted the "Shock Value" (no pun intended).

Pure Water - being that the Mole is comprised of nothing more than Hydrogen Oxide (2 Hydrogens bonded to a single Oxygen) is a non-conductive Molecule. There's no free Electrons in the outer valence which may be "knocked off".

Water does not become conductive, it only "holds" minerals which are conductive. This is done via the Solvent (Scraping) processes of Water (it's known as "The Universal Solvent").

Once a certain mass of Water scrapes and holds conductive materials, then the complete mass is a conductive material.

OK, so much for the Water thingee...

Conductive properties are - in our field of applications - what Materials will have a high conduction value (High MHOs, low OHMs), and we will use these Materials for our Power Conductors.
Our Insulating Materials will offer a very low conductive characteristic. We coat our conductors with those insulating materials to keep the smoke from leaving the conductors.


Even though we could hold a live conductor, which has THHN insulation on it, and not get shocked on a <1000 volt system, here are two things to consider:

<OL TYPE=1>

[*]The max. voltage for that insulation is 600 volts - what happens if we connect it to a system with potential of 6000 volts... will we still be able to hold it without a shock?


[*]With a non-contact circuit being coupled via a Reactive coupling effect, would this be possible if the insulation was 100% effective to stop the flow?
</OL>

Now we begin to see where the fine line of "Conductive vs Insulator" is.

Highly conductive materials have an abundance (sp???) of free Electrons in their outer "Shell(s)" of orbiting Electrons, and the energy required to move a free Electron from one Atom to another is somewhat low.
Another high conductance property is having lots more conductive structures than non-conductive impurities, mixed together in a given Mole of material.

Semi-Conductors are named this due to their ability to conduct highly in "One Direction", and conduct very poorly in "The Other Direction".

Conductance is a very interresting property of materials (or absence of materials - such as Vacuums), and characteristics which effect things include Potential Difference (Voltage), level of currents available, frequency, and yadda-yadda-yadda
<exit "Seinfeld"... >

Let me know if this makes sense, no sense, or your head spin!

Scott35

edited to correct a run-on sentence... hope I do not find others!

[This message has been edited by Scott35 (edited 01-21-2004).]

"Semi-Conductors are named this due to their ability to conduct highly in "One Direction", and conduct very poorly in "The Other Direction"."

AFAIK, they are named "semiconductors" because their bulk conductivity falls somewhere between that of conductors and insulators.

The unidirectional electron flow thing requires a junction between P and N type semiconductors, or regions with differing impurities which cause localized deficiencies or surplusses of electrons.

Scott,
It makes somewhat sense.

Edward

Good explanation Scott, two more paragraphs and we Jersey 'lectricians could get 3 CEU's for reading it!

Andy

Edward & Andy;
Thanks for the replies. Glad the descriptions were of help and somewhat understandable.

Need to point out that "NJwirenut"'s reply is valid - I "Space'd" on that part!
<D'OHH!>

Semiconductors fall somewhere between Conductors and Insulators. They Conduct - but do this rather poorly as compared to "True Conductors".

There is always a "Forward Voltage Drop" associated with a given Semiconductor device.
For instance, an LED may have a Forward Voltage Drop of 2.0 Volts, whereas a Silicon Power Diode may have a Forward Voltage Drop of 0.7 Volts.

The Peak-Inverse Voltage (PIV) for those same Diodes may typically be 50 Volts. This is the maximum voltage before the point where the "Reverse Biased" current will "Burst" through the device.

As to the original Q;

Wood will conduct very poorly, so it's more of an Insulator than Conductor.
As with Water, if the Wood becomes saturated with highly conductive minerals, the Wood structure becomes more conductive - but that raised conductivity is only via the concentrated elements.

I'll reference the EE Manuals for Conductivity Properties of Materials, then reply to this thread with a list.
Will include Electro-Static Potential levels of some Materials, which describe which materials offer static electricity abilities.

Scott35

Edward,
Try and tell a Lineman that wood does not conduct Electricity when the pole he is working next to arcs when a loop wire hits it, during the rain.

There are some grey areas in the electrical world. The insulating value of wood is quite variable, partly depending on its moisture content. If wood is clean, dry, varnished and carefully maintained, it can be very good insulator, as borne out by a past use on liveline tools such as hotsticks.

Nowadays, fiberglass and other plastics have taken the lead as tested to withstand 100 kilovolts per foot of length. It’s worthy predecessor, wood, had to hold off 70 kilovolts per foot without breaking down or “flashing over.” It’s fair to say that wood as a insulator is indeed one of those it depends situations, but can be quite good under the right conditions with careful application.

Bjarney,
I agree there mate!.
First Hot Stick I ever purchased was wooden and I still have it and use it to this day.
But there are situations where Fibreglass "feels" better!.

Did anyone see that History Channel program about Linemen? Was very cool show!

Per the EE manuals and properties of materials, man I should have looked before I spoke!

The data involved to post is mind boggling!

I'll list a bit of stuff as pertains to Conductivity:

Relative Conductivities Of Metals

[Element]..........[Relative Conductivity %]

* Silver........... 100%
* Copper........... 98%
* Gold............. 78%
* Aluminum......... 61%
* Zinc............. 30%
* Platinum......... 17%
* Iron............. 16%
* Lead............. 15%
* Tin.............. 9%
* Nickel........... 7%
* Mercury.......... 1%

Once I can compile a few charts, I'll let everyone know.
Also was hoping to include a chart for Electro-Static potentials of materials - such as which are of higher "+" potentials, and which are of higher "-" potentials.

Scott35

A very good book for learning electrical theory is "Electricty One-Seven".

This topic is addressed within 25 pages that contain only a couple of paragraphs per page and plenty of illustrations.

With quizes at the end of each chapter this is the single most impressive teaching device I have had the pleasure of using.

It is available for checkout through most libraries.