question about electrical resistance/conductivity

[gre]

What factors contribute to electrical resistance and conductivity at the atomic level?

[Klaynos]

The number (concentration) of 'free' electrons in the gas, and how easily these propagate across the material (how far they get before they hit something else and what that something else is).

[gre]

What about 'positive potentials' (i think it would be called or electro-negativity?) ... or positive charges, and magnetic fields from the atoms in the conductor.. This might just be part of having 'free' valance electrons.

 

 

Does the color of the wire have anything to do with it? I always thought the more reflective a metal was the more free electrons it had (and the higher the conductivity), but Nichrome wire is about as reflective as silver, but the resistance is high.

 

Thanks.

[Klaynos]

The positive charges (ion cores) do not move.

 

Normally conductors (in wires) are not magnetised, when they are you will get some curve on the path of the electrons from these fields (called the hall or quantum hall effects).

 

No the colour has nothing to do with it. Reflectivity of metals is related to this but is considerably more complicated so you cannot draw a direct comparison. Of course having said that a dull metal (like copper becomes if left open to the air) will be a poor conductor if you try and connect anything to it. This is not because copper is a poor conductor (it is actually a very good one) but because the copper oxidises (copper oxide is more dull than just copper so it looks dull) and copper oxide is a very poor conductor.

 

The drude model is quite a nice model of conductivity:

 

http://en.wikipedia.org/wiki/Drude_model

 

This can also be used using the drude-lorentz model to find the dielectric constant which we can use to find the reflectivity of materials. This only applies to metals at optical frequencies though.

 

http://books.google.co.uk/books?id=-5bVBbAoaGoC&pg=RA1-PA143&lpg=RA1-PA143&dq=drude-lorentz+model+dielectric+constant&source=web&ots=Hwqumzcf1w&sig=1ckJpyKXX9w91VqEo-s7XevauzY&hl=en&sa=X&oi=book_result&resnum=8&ct=result#PRA1-PA143,M1

[electricman6913]

tempeture is the bigest factor, eddy currents are a small factor. Also alternating magnetic feilds can impead electron flow. when gases become ionized that also changes resistance.

[einsteinium]

The number of valence shell electrons of a particular metal is one of the contributers to its conductivity

 

eg.. Gold has one valence shell electron (Au+), Copper has two valence shell electrons(Cu 2+)

In this case Gold is more conductive and less resistive, same applies to Ag+

It's the rate at which the delocalised electrons can swap places with other delocalised electrons when a current is applied.