# Current in circuits and conductivity

I'm really puzzled with a problem for a rather long time and I can't really seem to be able to solve it at all. It has to do with the electrons that move in a circuit.

We know that a battery builds up an excessive amount of electrons on its' anode, and that by connecting a wire between the anode and the cathode, the electrons will travel from the anode to the cathode, and so there will be a current in our simple circuit. So, in this scenario, the battery provides our circuit the electrons, and they travel through the wire from the anode to the cathode.

Know, we are told that conductive materials are materials that have a specific chemical structure, that allows them to have free electrons, being able to wonder freely in the material. We are told that if we apply an electric field (voltage) on such materials, the random motion of the free electrons inside the conductor will acquire​ a resultant velocity, and that its' direction will depend on the electric field that we applied.

We are also told that batteries supply with constant voltage a circuit. So, from whom are the electrons that are moving in a circuit coming? The electrons that are moving through a conductive wire in a circuit are the ones being originated from the battery alone (and have nothing to do with the wire's free electrons), or are they the wire's electrons, that move in a loop through the battery (with the battery supplying only the voltage needed and nothing else)? Or both?

In every answer I need a detailed physical explaination on what is actually going on. One thought that I had was that the battery is supplying its' electrons in the circuit, and when these electrons enter into the wire they bump into the free electrons of the conductive material, and they just exchange positions (the electrons of the battery) with the electrons of the material, but in this process we have electrons from the wire moving (something like the motion of charge inside a diode's junction). So the electrons from the battery actually collide with the electrons of the wire, then the moving electrons of the wire collide into other free electrons of the wire, and the current that is being created in the circuit is being created from both the electrons originating from the battery and the free electrons of the wire.

Thanks in advance.

## 2 Answers

Let's take a wire made of Copper. Copper has 29 electrons, 29 protons and 35 neutrons. The electrons are arranged in levels with 2, 8, 18 and 1 electrons.

Shell 1 has 2 electrons held by 29 protons. They can leave the atom if they can overcome attractive force of 29 protons.

Shell 2 has 8, held by 27 protons. To leave, electrons would only require attractive energy of 27 protons. Less energy than Shell 1.

Shell 3, 18, held by 19 protons. Again less energy than Shell 1 or 2.

Shell 4. Valence Shell. 1 electron held by 1 proton. This electron is far from the nucleus (in atomic terms) and can become a free electron if it overcomes the attractive force of 1 proton.

Heat, light, physical force and emf (electromotive force) can cause this electron to leave the copper atom. The electron becomes a free electron and the copper atom becomes a positive ion $Cu^+$. All atoms want to be balanced (the same number of electrons and protons).

With no emf, movement of electrons is random. They collide with full Cu atoms and are attracted by $Cu^+$ ions, becoming full Cu atoms. This is shown in the following animation.

Copper Wire - No EMF

But with an emf, we have two things: a source of electrons and a force to cause free electrons. Negative charge on negative pole repels free electrons and fills in $Cu^+$ ions.

Copper Wire - EMF

Simplified, emf creates free electrons and ions attract free electrons. The cross section of any wire has a massive number of atoms, so actual electrons move short distances, but net flow of electrons can flow long distances.

1A of current is 1 C/s, which equals a flow rate of $6.25 \times 10^{18}$ electrons/s. Scale of reality is much much larger than this explanation.

Best conductors (Silver [2, 8, 18, 18, 1], Copper, Gold [2,8,18,32,18,1]) have 1 valence electron.

So conduction or current is simply the flow of electrons.

If current stops, the majority of free electrons will be attracted to $Cu^+$ ions, so there will be few free electrons (aside from those released by heat, etc.). Any free electrons would spend time bouncing off of full atoms or insulators.

It's simple that as you know how battery builds up excessive amount of electrons on anode side thus

• the anode side has more electron than cathode this creates potential difference
• this pot.diff make electron in wire to move in a particular direction
• now when these electron moves they generate pot.diff. within wire which induces electron from anode to take place of moved electron
• this cycle continues till the time electron gets accumulated at anode

Hope you can visualise it