Have all wires got a set number of atoms in a given cross sectional area?

Question

If not does the number of atoms increase with a If so how does the current increase, is it because there is greater space between the atoms and therefore free electrons can ionise the atoms more easily?

Answer 1

The material of the wire is critical. Interatomic distances in metal lattices are unique to each alloy and the electron configurations are dependent upon the specific elements in the alloy.

Answer 2

Metals have a density, which suggests that if you are only looking at a single material that the number of atoms in a given cross sectional area are the same for that material from wire to wire.

That is not to say that each batch of that material is the same. Different additives or impurities in the metal would be expected to have an impact on not only the density, but the conductivity.

Another aspect of wires is the variability of the thickness of the wire and the manner in which the wire is pulled. Thin spots or even voids created by the pulling of the wire would have an impact on the ability of a specific wire to flow electrons.

For those familiar with aluminum housing wiring, something done in the 1960's, the aluminum, which is much less dense than copper, required a much thicker wire that copper for a given current. This would suggest that pure numbers of atoms in a cross section is important. Aluminum density is 2.7g/cu cm and copper is 8.96g/cu cm. Dividing this by MW of 26.98 and 63.55 respectively would suggest that Copper has 40% more atoms packed into the same dimension (cu cm, cu ft) and is likely one of the most important reasons a smaller cross section will convey more electricity.

Answer 3

No... put simply.

You need to examine gausses law to understand current flow along a wire. In essence, all the current flows along the surface of the material (ie the outside of the wire). You can play with this with composite materials but basically this is the case.

Having thicker wire (larger cross section width / area) does not change intermolecualr distances / forces between the atoms / molecules. You simply have more of the 'stuff'.

Current flow (conductivity of a material) is defined by the electronic structure of the outer most electron 'orbitals' / energy levels. In order for current to flow you need to be able to excite an electron free from the atom. typically this is from the outer most orbital / energy level / shell / band. This then leaves a space for another electron to occupy from another atom. The potential difference (measured in volts) supplies the electric field to induce directional flow of the electrons (otherwise they'd be flowing all over the show and current flow would be speradic if at all!!).

In insulators the conduction band is typically full and the energy difference between this band and the next band up is quite large. This means it takes a lot of energy to cause an insulator to conduct. For example, wire sheathing will insulate a small current / voltage flow but pass a bolt of lightning through it and the insulator is broken down and conducts.

Ultimately, your issue boils down to what is called the electronic configuration of the atoms / molecules involved, and more importantly, the configuration in the conduction band. This will vary depending upon what material you use for the conductor in your wire and not really on cross-sectional area. Heating through resistance plays with this a bit...

V=I.R

But lets keep this simple for now.

Answer 4

Number of atoms in a given cross sectionnal area for a material will be the same.

In metals there are electrons which are free to move from one atom to another atom.

They are called free electrons. These are the electrons which are not bound to the atoms.

When there is no current, all free electrons are at random motion from one atom to another atom.

However at any time the total number of electrons for one atom will not cahnge, even when there is current.

When n number of electrons leave an area of cross section n number will be comming to the area of cross section.