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| Does current flow through a Battery? |
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| ejeffrey:
--- Quote from: GlennSprigg on October 19, 2021, 11:42:36 am ---"Notice how the GAP between the blocks appears to be moving to the Left! That is the movement of Positive Holes!!". Ggrrrr... Even then at 16, I would pull them up, and tell them to start talking about 'Electrons', and that drawing 'standards' even 'today', should be changed !!! |O --- End quote --- Holes are completely OT to the question at hand which is electrochemical cells, but even if we redefined positive charge to mean electrons (which there is absolutely no reason to do), we would still have the concept of holes -- they would just be negatively charged. Holes are not an annoying wart that we have to deal with because of the "wrong" charge convention, but an essential concept in semiconductor physics. But in a electrochemical battery we have physical motion of charged ions through the electrolyte. Depending on the battery chemistry these can be positively or negatively charged. You don't have to try to reason about this from first principles or resort to analogies, you can just read about what exactly happens in a battery. I really, really, really wish high school physics teachers would stop saying that "Ben Franklin got the conventional current definition wrong but we are stuck with it" -- this places way to much focus on electrons rather than the idea of fields and net charges which is really what matters. The fact that in metallic conductors the electrons are the mobile charge carriers is irrelevant unless you are studying solid state physics. |
| TimFox:
Exactly. Electricity was discovered and quantified long before a particle that is very important in electricity was discovered and named the "electron". |
| GlennSprigg:
Aaarrgghh.... I 'get' what people are saying, but still think there is a miss-communication of ideas/concepts here... :palm: Old Scottish song... "I'll tak the high road and you tak the low road"... Oh well, what ever people feel comfortable with. So far, no-one here has dared/tried to counteract what I said about a 'Capacitor', (which IS basically behaving like a battery, but not chemically), where there is NO actual flow of 'charge' within it, through the Dielectric, and that any 'flow' is EXTERNAL through an attached circuit, and 'then' back to the other side of the Capacitor??? I do not grasp the problem of this thinking??? If I'm wrong, then I'll probably go to my not far off grave believing what I believe, so what does it really matter! hahaha... 8) |
| TimFox:
"Displacement current" was discovered in the 19th Century and is included in Maxwell's Equations to explain the current through a capacitor. Ionic current in batteries is similar to ionic current in salt-water solutions. Current is a more general term than the motion of electrons in a vacuum tube. |
| TimFox:
Here is a thought-experiment to show the importance of displacement current through a capacitor in the real world. 1. Set up two parallel plates, each 10 cm by 10 cm, spaced by 1 cm, inside a transparent jar that can contain the sand discussed below. 2. With air between the plates, k = 1 (dielectric constant), the capacitance will be approximately 0.9 pF. (Even without a material dielectric, there exists a polarization field between the plates. When we add material below, the polarization increases for a given applied voltage.) 3. Connect an AC generator (output impedance 50 ohms) through this capacitor to a 50 ohm load and AC voltmeter. The total circuit impedance is 100 ohms (resistive) plus the reactance of the capacitor. 4. At 10 MHz, the reactance of the capacitor is about 18 k and dominates the total impedance of the circuit. 5. Now, start adding SiO2 powder (sand) to the region between the plates. It is a good insulator, but solid SiO2 has k between 3.7 and 3.9. Since the powder has a lower density than the solid, assume k = 2.5. As the sand level increases from zero to fill the gap, the capacitance increases from 0.9 pF to 2.2 pF, and the current in the circuit (measured by the voltage across the 50 ohm load) will increase by almost the same factor as the reactance decreases. With these parameter values, the voltage across the capacitor itself is almost constant (since its reactance is much larger than the total resistance of 100 ohms), but the displacement current increases with the increased polarization in the dielectric. Current continuity includes the conduction current through the two resistors and the displacement current through the capacitor. Moral: just as there are many flavors of ice cream, displacement current is one type of the general phenomenon known as "current", along with ionic current, conduction current, beam current, etc. |
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