Peter G. said:
I just needed a very basic explanation of the function of the battery. I know by means of chemical reactions (involving electron flow as a more reactive metal gives out electrons, losing negative charge, thus, becoming positive and a less reactive metal takes those electrons, negative charge, becoming the negative terminal) I wanted to know if this "terminal set up" sets up an electrical field that is responsible for attracting the delocalized electrons in the wire, the charge.
Essentially, yes!
(but be careful.)
The cathode (positive terminal) of the cell (a.k.a. "battery") develops a very small positive charge on it, attracting electrons from the wire. Likewise, the anode develops a small negative charge repelling electrons away from it, into the wire.
I've attached the diagram below to make sure we're both on the same page with what we are talking about.
Part of your question about the cell, but let's discuss the other parts of the circuit first (get the low-hanging fruit).
Notice I added a resistor to the circuit. This is important. If we were to model the cell as an ideal voltage source and connect the terminals together directly with an ideal wire, we'd end up with infinite current. In a real-world situation, the current wouldn't be infinite, but it would still be very large and possible cause your circuit to melt or start fire. The reason it wouldn't be infinite is because the cell and wires themselves actually have a small amount of resistance associated with them that would limit the current. But we're not trying to model those things here, so I added an external resistor to keep things simple.
//// Wire AB
- The wire is a conductor. The electric field inside a conductor is zero. However, electrons are able to move through the conductor (and in a typical circuit like this the generally move very slowly on average -- maybe a centimeter or less per second). But for every electron leaving to the left into the cell, there is another electron entering from the right from the resistor.
- The total charge on the wire is essentially zero. Even though the electrons are moving, for every electron in the wire there is also a proton in the wire. So there is no net charge on the wire. (There might be a very, very small net positive charge on wire AB. This is because wires AB and CD act like a very, very weak capacitor. But for our purposes we can ignore this very small net charge.)
//// Resistor
- As the electrons move from D to B, they lose potential energy. Pretend you and your friends are electrons, and you all fall down a very steep hill. Also imagine that there are many, many other people in front of you that have just fallen down the hill, and many others behind you about to fall down the hill. Gravity is the force that accelerates you down the hill, but don't accelerate down the hill uniformly. Instead you bounce off rocks and boulders, not to mention smashing into your friends repeatedly. Oh, the humanity! The end result is that your initial potential energy gets converted into thermal energy from all the crashing and bumping.
- There is an electric field in the resistor, and thus a potential (voltage) across the resistor. This is equal to the electric potential of the cell.
//// Wire CD
- See wire AB above, for the same concept, just reverse the direction. The only real difference is that electrons on wire CD will have a higher potential energy than those on wire AB. It's analogous to wire CD being on a level plateau near the top of steep hill (the resistor) and wire AB being a level plateau at the bottom of the steep hill.
//// Cell (battery)
- This is where things get a little complicated.
- Ions exist in the electrolyte solution from the beginning. The reason the ions don't combine and neutralize with themselves is a matter of chemistry.
- The ions in the electrolyte solution chemically react with the anode and cathode. This causes new compounds to form at one or both of the electrodes.
- These new compounds can often "plate" the electrode causing its exterior to be something different than it was previously.
- Depending on the cell composition, the surface of an electrode might even dissolve in the process, becoming part of the solution in ion form.
- Cations move to the cathode and anions to the anode mainly through the process of diffusion. As soon a few ions of a given type react with the corresponding electrode, they are no longer ions. Other ions move into take their place via natural diffusion.
- Reactions at the catode leave a leftover positive charge. Reactions at the anode leave a leftover negative charge. Since the electrodes are conductors, electrons are able to leave the anode (removing the net negative charge on the anode); or in the case of the cathode, be neutralized by an entering electron.
Now look what happens when we make the resistor very large -- or even better, let's just remove it from the circuit.
In the above circuit, a few chemical reactions take place leaving behind the leftover charges on the electrodes. This
does cause an electric field. This field inhibits the cations from reaching the cathode, and the anions from reaching the anode. The end result is that no more chemical reactions take place (well, almost no more), and the cell reaches a state of equilibrium.
I also need to know that they give the electrons electrical potential energy as a result of their stored chemical energy transformation.
The chemical reactions involved so far are chemically spontaneous. The results of the reactions produce energy, in the form of electrical potential energy of the electrons at the anode (and in wire CD).
Now you might be asking, "why don't the reactions spontaneously happen in reverse? Energy is conserved either way, so why does it only happen one way spontaneously?" The answer has to do with entropy and the second law of thermodynamics. Only the way described above causes the overall entropy to increase.
But my main doubt lies in the wire:
I wanted to know what is charge in the wire?
The net charge on the wire is essentially zero*. Yes, the wire has a bunch of conducting electrons within it. But also has essentially the same amount of stationary protons too.
*
(There may be a tiny excess charge on the wire, but as I mentioned before we're going to ignore this.)
You'll need quantum mechanics (or at least solid state physics to really show this). Atoms in a conducting material contain a nucleus with a positively charged nucleus, which contains protons and neutrons. Most of the electrons in the material are bound to the atoms and cannot move around. But some of the electrons are shared between atoms. And can move from one atom to the next. This is known as the conduction band. A couple of points:
- Not all of the electrons in the conductor are in the conduction band. Most of them are bound to the atoms and are not free to move around.
- The electrons that are in the conduction band do not result in excess charge. The total number of electrons in the material (both bound electrons and electrons in the conduction band taken together) are essentially the same in number as the number of protons in the material. The net charge is essentially zero.
I know one coulomb of charge is 6.25 x 10 ^18 electrons. My doubt was, are these electrons, that make up the one coulomb of charge the delocalized electrons, the charge carries (which I guess are charge, and are called carriers because they move) or the electrons moving from the positive side of the battery (e.g.: Zinc giving out two electrons forming a Zn 2+ cation)
Both (if I'm understanding your question). For every electron leaving the anode of the battery, there is another one entering the cathode. The total charge of the battery remains constant (zero). The total charge of the wires/resistor remains constant (zero).
Let's just look at the cathode in isolation for a moment. Inside the battery, the cathode can gain positive charge by either dissolving, giving off part of its mass in the form of anions, or plating, increasing its mass by combining with cations. (Which one actually happens, or both, depends on the makeup of the battery). Whatever the case, the cathode can gain positive charge via chemical reactions. The important point is this: in steady state, the increase in positive charge due to chemical reaction is exactly counterbalanced by the increase in negative charge caused by electrons flowing in from wire AB. Thus in steady-state, its net charge remains constant.
Good luck!
