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Posted on 2021-04-28 12:00
I learned in a Khan academy video that electrical current is really just electrons that get bumped loose from the orbit of an atom, making the atom into a positively charged ion. Since the negatively charged electron hit the road the atom now has fewer electrons than protons and so it is said to be positively charged. Free electrons will pop right into the empty slot left behind and return it to a neutral charge... when the reverse happens -- an extra electron enters the orbit of a normal atom, that atom becomes negatively charged because of the proton/electron imbalance and is said to be a negative ion.
The idea of some atoms having electrons that are easy to pop around -- like the atoms in conductive materials -- basically makes sense. Mims further explains how that popping around can happen with a series of experiments though, and it's interesting to think about how so many different physical ... processes I guess? can stimulate electrical movement. Mims calls out friction, light, heat and chemicals specifically. Thinking in those terms makes the idea of current a little less mysterious...
The other major breakthrough for me so far with this chapter is static electricity! I never really thought much about it, or what it actually is... but knowing all static electricity means is that there are electrons resting on some surface (a negative static electrical charge which will flow into the first thing that conducts toward a positively charged ion) OR that the atoms on the surface of some material all got their electrons knocked off orbit and so the surface consists of positively charged ions, just hanging out there being a positive static electrical charge.
That actually makes current which I've struggled with a bit in the past feel understandable.
Still, I don't yet grok these relationships. The metaphor of water pressure for voltage makes sense on its own -- it's intuitive to think of potential charge in terms of water
pressure caused by the weight of a reservoir pushing itself through a lower spigot and the speed of the water rushing through being the current (this is the easiest to grok IMHO since it's literally a measure of electrons per second that pass some given point) and I also basically see how the analogy of resistance being the friction caused by forcing the water through the spigot since I can imagine different materials having more or less difficult atomic landscapes to circumnavigate... but I still don't really grok potential energy and voltage in physical terms. Is it just a measure of static charge at the starting end of DC flow?
I basically get "power" as well which I don't see used much in things that I've read, but a definition of basically "the component that does the work" makes sense to me.
Speaking of DC flow! This chapter explained the difference between AC and DC current so clearly I feel like I must have it wrong since it's so simple... anyway my understanding is that all DC / direct current means is a current that flows in one direction. There is also an associated voltage drop as the electrons flow through the system and experience resistance... at least I think that's how the voltage drop happens?
AC or alternating current is interesting. Mims says it is typically produced by spinning a coil inside a magnetic field, though how exactly that produces the alternation of flow from one direction to another I'm not sure. It's clear enough though that the oscillation produces a sinewave motion and I at least can acknowledge that there is an additional property of AC that tends to encourage electron flow in adjacent sections of the circuit, and so is suitable for long-distance power transmission where DC would suffer from a voltage drop from the resistance caused by traveling a great distance over the wire. (Which also jives with what J was telling me about a huge mistake I made in my original approach to a little solenoid circuit which placed the power source next to the controller instead of the solenoid... and the voltage drop made the solenoid behave poorly. (Gummy action, sometimes barely activating, etc.)
The really mindblowing section of this chapter though is the page that describes simply how to make a basic solenoid AND a motor (of sorts) from just a plastic straw, iron nail, copper wire and a battery. So OF COURSE I'm going to play around with that! Amazing.