What follows are ideas I have along with established concepts.
Capacitors
A capacitor consists of two metal plates which are separated by an insulator. A capacitor is charged by a battery (Chabay, 765)). What follows is an explanation about how to charge a capacitor using a copper/zinc voltaic cell. It’s assumed that the capacitor plates are made of the same type of metal, have the same surface area, and are both initially electrically neutral. One capacitor plate is connected to the zinc anode by a wire, and the other one is connected by a wire to the copper cathode. The electrodes aren’t connected to each other by a wire because that would disrupt the charging process. Each electrode takes electrons from the capacitor plate it’s connected to. Aqueous copper cations in the cathode half cell ionic solution take electrons from the cathode by depositing on it, aqueous zinc cations in the anode half cell ionic solution take electrons from the anode by depositing on it, and the salt bridge neutralizes the ionic solutions as this occurs. This causes the capacitor plates to increasingly become electron deficient and to therefore increasingly resist giving up electrons. However, because the copper cathode is more electronegative than the zinc anode, it takes electrons from the capacitor plate it’s connected to faster than the zinc anode takes electrons from the capacitor plate it’s connected to. So, the capacitor plate the cathode is connected to becomes more electron deficient than the other capacitor plate. This causes the net positive electric field of the cathode capacitor plate to be greater than the net positive electric field of the anode capacitor plate such that there is a net pull on electrons of the anode capacitor plate by the net positive electric field of the cathode capacitor plate. The extent or magnitude of this pulling represents the difference in electronegativity between copper and zinc.
For example, if the copper cathode takes three electrons from the capacitor plate it’s connected to for every one electron taken by the anode from the capacitor plate it’s connected to, then the net effect for that time interval is that the net positive electric field of the cathode capacitor plate pulls on two electrons of the anode capacitor plate. So, although the copper and zinc electrodes weren’t associated with each other before because they weren’t connected together by a wire, they become associated with each other after the capacitor plates get in contact with each other through the electric fields. As the difference in electron deficiency between the capacitor plates increases, the net positive electric field of the cathode capacitor plate increasingly pulls on electrons of the anode capacitor plate. For example, using the previous analogy, if for every one electron taken by the anode, the cathode takes three electrons, resulting in the cathode taking two more electrons than the anode, then when this happens again, the anode has taken two electrons total, whereas the cathode has taken six total, resulting in the cathode taking a total of four more electrons than the anode. When this happens a third time, the anode has taken three electrons total, whereas the cathode has taken nine electrons total, resulting in the cathode taking a total of six more electrons than the anode. So, the process accelerates.
This causes electrons of the anode capacitor plate to pile up, so to speak, in the part of the plate that’s closest to the cathode capacitor plate. However, electrons don’t actually go on top of other electrons, which would cause there to be varying distances between electrons and adjacent nuclei. Instead, they merely get pressed or crammed closer together side by side in the same layer thereby maintaining the same average distance from adjacent nuclei. So, the electrons of the anode capacitor plate become increasingly concentrated in the part of it that’s closest to the cathode capacitor plate, thereby accelerating the electron deficiency of the rest of the anode capacitor plate. This makes it even more difficult for the anode to take electron density from it. This occurs until the situation is reversed and the anode capacitor plate actually starts taking electrons from the anode. That is, the electrical component overrides the chemical or electronegativity component. The cathode continues to take electrons from the capacitor plate it’s connected to until the excess positive charge in the capacitor plate increases to the point that the cathode can no longer take electrons from it. That is, the electrical component reaches a stalemate with the chemical or electronegativity component. So, the extent that the capacitor plates are charged, that is, the voltage between them, is the same as the voltage of the voltaic cell. It’s equivalent to the copper/zinc voltaic cell going until equilibrium is reached, and the voltaic cell dies. However, it’s in the opposite direction because the voltage of a voltaic cell is greatest at the very beginning of the redox reaction process since the chemical concentration gradient or disequilibrium is the highest then. Basically, the voltage of the voltaic cell gets converted into charge separation in the capacitor plates.
It’s the case that the concentration of excess positive charge that’s pulling electrons up against the part of the anode capacitor plate that’s closest to the cathode capacitor plate is greater than that electron density. This is because since electric field strength diminishes with distance, the portion of the electric field of the excess positive charge that reaches the anode capacitor plate across the gap is weaker than what’s closer to the excess positive charge. So, the density of the electrons up against the near side of the anode capacitor plate is less than the density of the excess positive charge holding them there. That is, there’s more excess positive charge on the cathode capacitor plate than there is excess negative charge on the anode capacitor plate due to the fact that electric field strength diminishes with distance and the electric fields have to reach across the gap distance in between the capacitor plates. The cathode pulls electrons from the cathode capacitor plate, which pulls electrons from the anode capacitor plate, which pulls electrons from the anode.
In order to discharge a capacitor, the two capacitor plates get connected together by a wire. The excess positive charge of the cathode capacitor plate imposes a certain amount of pressure on the wire, primarily on its interior. It’s primarily in the interior due to the more confined situation of the interior atoms compared with the surface layer ones which causes electrons to more rapidly travel through the interior than through the surface layer of atoms. This pressure extends uniformly throughout the wire from one end of it to the other. So, the end of it that’s connected to the anode capacitor plate pulls on electron density of the anode capacitor plate. It sucks excess electrons on the anode capacitor plate into itself at the junction or interface like a vacuum cleaner.
Actually, what happens is that the pressure in the wire also gets felt in the anode capacitor plate through slight sequential electron displacements or shifting in the interior which causes the anode capacitor plate to suck excess electrons on its exterior into itself. These then travel through the interior and cross the junction between the anode capacitor plate and the wire into the wire’s interior. The suction pressure is mainly towards the outer side of the anode capacitor plate since this is more directly in line with it. The electric field lines which represent actual electron movement instead of the type which emanate from individual charged particles have to curve less in this direction which is more energy favorable. So, the suction pressure is weaker towards the sides of the anode capacitor plate and especially towards the inner side of it. In order for excess electrons to be taken from off the inner side of the capacitor plate, the electric field lines which represent the pressure have to curve a lot which is less energy favorable. So, the electric field lines there are much less dense, and this drastically diminishes the pressure magnitude, the ability to suck exterior electrons into the interior. In order for electron travel through the wire’s interior to be preserved and to be most efficient, the wire’s surface layer of atoms has to remain electrically neutral, can’t have excess positive charge, because the tugging of this on interior electrons would disrupt interior current flow. It’s the same situation as with a voltaic cell.
The cathode capacitor plate isn’t able to impose on the wire the same magnitude of pressure as it itself has due to resistance by the wire. So, the process of the wire sucking up excess negative charge on the anode capacitor plate, or rather pulling electron density from the anode capacitor plate that’s pulled from the plate’s exterior by the plate itself, is more gradual. This allows for some of the excess electrons to escape from off the outer side of the capacitor plate where their concentration is by far mainly located and pour over the sides of the capacitor plate onto the inner side of it and then along the exterior of the wire itself to the cathode capacitor plate. Their movements are entirely due to repulsions with each other where they seek to establish electrostatic equilibrium with each other. They can do this because they can only get sucked into the interior at either of the capacitor plates, not on the wire. Their presence on the exterior of the wire acts like a wire sheath that helps preserve the interior current. The first part of the cathode capacitor plate that they reach is the inner side of it. This region has a major pressure shortage because it’s located at where the pressure lines have to curve a lot, being out of the way of the main pressure direction which is at the outer side of the capacitor plate. So, the excess electrons which traveled along the exterior of the wire enter the cathode capacitor plate at this low pressure area thereby contributing to neutralization at a region that doesn’t get enough electron coverage or exposure through the interior.
Works Cited:
Chabay, Ruth W., Bruce A Sherwood. Matter and Interactions, 4th ed. Wiley, 2015.