I was hoping for something to an article helping you understand. A list of things is it not helps, but only somewhat.
This is the exact opposite of good pedagogy. Ironic, since it's supposedly aimed at educators.
> If you were not confused before reading any of it
If you watch discarded film-clips, all two seconds long and many of them backwards, expect to be confused.
The actual articles are at http://amasci.com/ele-edu.html
The article dies little if anything to help K6 educators (or students) understand electricity.
I think K6 should teach something good along the lines of safety/fun, and 6-12 something along the lines of practicality.
I learned Ohm's law when I was about 10 via "multi-kits" like so many other kids of my generation. This basic knowledge of electricity has served me well over the decades. It is seldom taught in school. Why?
I still don't really understand Maxwell's equations, but neither does your average electrician. That doesn't mean your average electrian doesn't have more knowledge about practical electricity than your average scientist who does understand Maxwell.
The finished article(s) are listed at http://amasci.com/ele-edu.html
And heh, about maxwell, if someone claims to understand Maxwell's Equations, just sadly shake your head, then adopt an archly superior stance, and haughtily inform them that those four are HEAVISIDE'S equations, while Maxwell's were twenty equations based on the latest 1800s math-fad: Hamilton's "quaternions." If they don't understand THOSE, they don't understand Maxwell! (And now we've avoided having to admit we've never read any of them. Hee!)
For those who didn't read:
"BELOW are my original, very crude and totally unedited 1986-1989 notes and "raw data" for...
My actual completed Electricity articles are: http://amasci.com/ele-edu.html
(Why the downvotes? Is math truly that scary for a forum of software engineers?)
That the water analogy works so well also has little to do with the Maxwell equations, if I'm not mistaken, I think it has more to do with the conduction electrons behaving more or less like a (highly degenerate) gas.
You don't need curl and divergence to figure out whether you can turn on your microwave and coffee maker at the same time without tripping the circuit breaker.
For most practical tasks, even the fact that we're working with AC rather than DC can be glossed over. People can plug in 120 V into Ohm's law and get the right result even though actual voltage fluctuates between -170 V and +170 V.
This article is simply not aimed at you, it is directed towards experts. So your complaint is a bit like complaining that “C# In Depth” doesn’t sufficiently explain basic syntax.
Another is Darren Ashby's "Electrical Engineering 101: Everything You Should Have Learned in School...but Probably Didn't"
Are we teaching electricity the wrong way 'round?
Understanding electricity and circuits: what textbooks don't tell you
FIELDS OF ELECTRONICS: understanding circuits via physics
I have watched many YouTube videos. I understand that electricity is electrons moving through a conductor from “+” to “-“ but am at a loss of why they move and why do we have two measurements for one thing.
The water analogy is most useful at this level (despite being wrong in most respects, it instils a basic working understanding good enough for the householder).
Think of a waterfall. Wait, think of two: a very high one with just a thin stream of water, and a low one, maybe a foot high with a torrent of water flowing over it (a weir).
Voltage is the height of the waterfall: a stream of water at the bottom of a very high waterfall will feel more painful than a stream from a much lower one.*
Current is analogous to the amount of water flowing over the waterfall - the river's current.
Multiplying voltage by current, you get power: the ability of the waterfall to do useful work.
(A very high waterfall with hardly any water flowing over it won't be able to turn a water wheel very quickly, and nor will a very low waterfall with a lot of water flowing over it. You need both voltage and current to do useful work.)
Re the movement of electrons: in fact they move very slowly on average under the influence of an electric field, but by their "bouncing against" their neighbours, the electric impulse
is transmitted quickly through the conductor.
* An alternative analogue for voltage is water pressure, and indeed in some languages voltage is referred to as pressure.
The most common place I can think of is in the HT (High Tension) leads leading to a car's spark plugs: https://en.wikipedia.org/wiki/High_tension_leads
German has this too: voltage = Spannung = tension.
This must go right back to the earliest writings on voltage as a concept.
A simmilar problem in spanish was "amperaje" (amperage) which is not much heard any more except very colloquially among electricians; the standard term is "corriente" (current).
However, the units and letters are somewhat confusing for the students:
V(oltage) = E(lectric field?), unit is Volt, is refered as tension of potential differece.
A(mp) = I(ntensity), unit is Ampere, is refered as corriente.
P(ower), unit Watt, is consistent, as is refered as potencia (power).
When you apply a voltage across a conductor it generates an electric field, and the electric field propagates at the speed of light (it’s an EM wave). I could be wrong, but I think that is why the electric impulse transmits quickly even though the drift velocity is so slow.
Each electron moves slowly, but they all move approximately in the same direction st the same time, so the net effect is to move charge berry quickly, right?
Like a bucket brigade where everyone passes water to the person on their left. You move a bucket 3 feet per second, but together everyone moves a bucket worth of water a hundred feet per second.
If electrical properties propagated at the drift velocity, there'd be an appreciable delay when you flipped your light switch.
In the process, the electrons gain kinetic energy, and if you’re clever you can extract this energy to do useful work. Voltage  is defined as joules per coulumb, where joules is a measurement of energy, and coulomb is a measurement of electric charge — one coulomb is the charge carried by 6x10^18 electrons. A voltage is always between two points, so if the voltage difference between point A and point B is 1V, then moving 6e18 electrons from point A to point B will produce 1J of energy; or, conversely, it would require 1J of energy to move the electrons back “uphill” in the opposite direction. (Actually, that’s sort of backwards because electrons carry a negative charge and so flow from the negative side of a battery to the positive, but that’s not terribly important right now.)
Current  is the rate at which electrons are flowing, defined simply as coulombs per second. You can calculate the rate of energy flow by multiplying voltage (energy per unit charge) by current (charge per second) to get watts , which is defined as joules per second.
If you want to learn more, there’s lots of excellent resources online — but if you really want a solid understanding from first principles, you might be better off taking an introductory physics course at a community college.
In a battery, the energy moves through the external circuit because the internals of the battery have been arranged so that an energy releasing chemical reaction is completed when that happens.
In an alternator, a conductor is moved through a magnetic field, which induces a current (this arises out of the properties of magnetic fields; https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction ).
Voltage and power are related by current. Power = voltage x current.
The amount of current that flows through a circuit depends on the voltage potential and the properties of the circuit. Our bodies aren't particularly good circuits, so lower voltages won't push much current through a circuit that includes it. A car battery isn't a big electrocution risk, it is dangerous because it can release a lot of energy quickly (it has fairly high power). Somewhere around 50 volts, current does start to flow through our bodies, causing problems even at relatively low currents (and thus low power), heart disruption and such.
Watts are a measure of energy, just different units than calories or BTU.
Voltage is a measure of difference in _potential_, and amperage is a measure of current being moved. So electrical energy depends on a bit of both.
Beyond a certain voltage, it can be somewhat shocking. High enough and it can jump out at you.
And it can be badly damaging.
Also depends on how conductive you are at the time, conductance is the opposite of resistance.
Also depends on how much amperage is available from the source, if the source is fused for 1 amp maximum it would be less risky than higher amperage fuses.
Like with household wiring, if you get shocked and are conductive enough for significant amperage to be passed through your body, the total wattage could be enough of a fraction of a space heater's dissipation to roast the tissues which are involved with conducting the current.
Simply because there's enough amperage available at that voltage to get a space heater red hot, and the circuit breaker will not trip unless you are conducting more than that.
OTOH, sensitive organs can be upset by much lower amperage if it passes along lines where the organs are nearby.
For instance if you work on an electrical box and take a shock from your right hand to your right elbow, it's mainly going to hurt that one arm.
But contact the same two points, one to each elbow, and the heart is at risk much more than before, since the current has to pass through your torso to complete the circuit.
Sorry to be pedantic, but watts are a unit of power, not energy. Power is energy divided by time. The unit of energy is a joule (or, more commonly in household terms, a Watt-hour).
At least it's not just me that thinks the usual explanations are lacking.
edit: I'm not sure, on second thought, how far you can really go with that. Lightning clearly has directionality to it.
The growth of lightning is much like a growing metal dendrite-crystal.
Also, when lightning leaps rapidly upwards, the electrons INSIDE the lightning are flowing slowly downwards. The extending tip of a lightning-streamer is not an electric current, it's more like the moving tip of a growing fracture.
> ...mistaking the wave for the medium. Is "electricity" the electrons, or is it the wave of electron-flow, or is it energy that flows THROUGH a column of electrons. Think of how difficult it would be to understand sound waves and air pressure if we had just a single word that meant both "sound" and "wind" and "air."
Wind : DC
Air : conductor
Wind is like electrical current in the sense that you set up a pressure difference between one point and another, and then you open up a little path for the electrons/air molecules to flow through, then they will move along that path, and the amount of air molecules/electrons flowing past a point per second is the current/wind. That’s the analogy.
The key units are amps (current) and volts (voltage aka potential difference). In the commonly used water analogy voltage is water pressure, and current is amount of water that flows through per unit of time.
It's the current that kills you. But voltage and current are related, in many cases by Ohm's law: current is proportional to voltage, with coefficient called conductance (the inverse of which is resistance). That's why high voltage is more dangerous.
In all cases, what hurts you is current. Current means electrons are flowing through you. As mentioned there are at least a couple of ways that current can affect you adversely. So it needs to be either a large enough current (so more electrons flowing), or a current going in the wrong place (across the heart).
So what makes current flow? Or, why do the electrons "want" to move? Voltage. A car battery has plenty of energy in it that could kill you in either of the two ways, but at 12V there's not enough voltage to get any current flowing through your body.
Voltage is the existence of an imbalance. Electrons "want" to be in a place where they are balanced with a positive charge. A battery represents a structure that is very imbalanced but the electrons are not able to move anywhere until the two ends of the battery are connected with a conductor. There are many ways that these imbalances arise but they are ultimately always the result of energy going in. When the imbalance is resolved the energy comes back out.
To hurt you a voltage also needs to be sustained long enough to pass enough current. A static shock is due to a very high voltage existing which it causes current to flow and why you can feel it, unlike the car battery. However, in an instant all the current has flowed and the voltage is gone.
So the answer is a high enough voltage and enough energy to sustain that voltage. Mains electricity can hurt you because it's high voltage (>50V) and can sustain that voltage all day long. Lightning can hurt you because it's very high voltage and can sustain it long enough (and that's only an instant) to cause serious injury.
It won't kill you quickly, though.
Actually they move from "-" to "+" :)
"Electricity" is one of those terms that doesn't really have a specific meaning. From what i see, we use it to group all the electromagnetic things that.. i guess deal with "loose" electrons.
As for the actual question, first i'd have to explain "electric current". Current (in Amperes) is just the flow of electrons. As in how many electrons flow through some plane over time. In practical terms; how many electrons flow through a wire, where the "plane" is the diameter of wire.
Voltage is a force. Imagine that the electrons weren't points that repealed each other, but were instead balls. You fill up a pipe with balls and push on one side of it. The force you are pushing with is the "voltage". You can also imagine this with water, where the pressure is.. well it's all the same really when we get "low" enough. Note that electrons, unlike balls and water, don't really have mass.
Wattage is power. It is how much energy is.. transmitted over time. You pay your bills in Watt * Hours, but you might as well pay it in Joules. It shows you how much power you can expect from a machine. Wattage is calculated by multiplying Voltage and current, as in how hard you push and how many electrons you push per time. In water terms, it is the speed of the water multiplied by how big the river is (or pipe).
So they are useful units of measurement, just as any other metric unit of measurement. In fact Ampere is one of the seven basic units of measurement in the Systeme international d'unites (SI, often called "metric").
The one that actually hurts you is the current. The thing is that Voltage "pushes" the current, so one might rightfully think that "high" Voltage is the dangerus one. But again you can touch a 100000 Volt sphere on top of a Van de Graaff generator, because it doesn't have enough electrons in it to make a current "big" enough to kill you. The current across the heart, that is enough to stop your heart, is about 50mA (as far as i remember), and that is very little current. Your heart is in between your hands, so you would need to hold "+" in one hand and "-" in another for current to go through it. You can also die from poisoning if a large current burns your flesh, and other similar bad things. If you think there's a danger from electricity, use just one hand so that the current goes through your legs, missing the heart (also watch for the top of your head, because brain). If the voltage is really high, like a transmission line cable falls right beside you, put your feet together and hop away. Like 10 meters away should be fine, idk. To be clear, you can touch the leads on your 12 Volt car battery and nothing will happen to you, in spite of the car battery being easily capable of delivering a big(ish) current of a 100 Amperes (but if you connect the leads with a wire, it will melt and burn you).
For fun i measured my palm to palm resistance just now. It's ~2 mega Ohms currently. So saying i need 50 mili Amps through my heart to stop it, i'd need (V = 0.05 * 2000000) 100000 Volts minimum. But that is for "direct" current (DC, not AC), and it doesn't take a lot of other things in to account. In reality 220 Volts AC could be enough. On the other hand, i know many people survived grabbing the "hot" wire and ground with their other hand, and the only one i vaguely remember died has fallen of a ladder because of the shock.
So in short; Wattage is power, Voltage is.. force, they are used to calculate things involving a lot of stuff (and safety), and the current hurts you because Voltage told it to.
PS Feel free to ask if something is not clear, i misinterpreted your question, something else you want to know or expand upon, etc, etc
Watts = volts * current (amps). It's hard to compare words like "force" and "quantity" for volts and amps, but here's maybe a practical definition.
High voltage is dangerous because it can leap through air (arc) to form a circuit. If part of that circuit is _you_ (like, from a high-voltage wire, through you, to the ground), then you can be made dead, quite quickly. That's why high-voltage (sometimes called "high-tension") wires are carried by tall towers with the wires far apart -- if the wires were closer together, they could arc between them and short out.
Essentially, high voltage overcomes insulation -- whether the insulation is air (for high-above-ground wires) or various forms of plastic (for wires buried underground). That's what makes it dangerous, and why electrical panels have warnings that say "Danger: High Voltage".
But even very high voltage won't hurt you if the current (amps) is too low. But "low current" isn't something you typically encounter in, for example, household AC wiring because the supply of current is generally very large.
So high voltage can kill you, but only if the current (amps) is high enough. In most practical situations where you might be exposed to electricity from the grid, the current is plenty high. That's why the signs say "Danger: High Voltage" and not "Danger: High Amps" or "Danger: High Power" (watts).
But how high is "high"?
A 12-volt car battery (I wonder how long that term will be meaningful...) isn't very high voltage. You can safely put your dry fingers across the terminals of a 12v battery and not feel a thing.
On the other hand, the 120-volt (or 240-volt) electricity coming out of a wall socket is most definitely unsafe to grab with your dry fingers. I've been accidentally shocked dozens of times by 120v electricity, and it is attention-getting. It can kill you fairly easily if, for example, the alternating current of the electricity causes your muscles to contract, forcing you to hold on ever more tightly to the wires. Usually, it's your heart in the path of the current that takes the, um, beating. If you get a shock across just the one hand that you're sticking accidentally into a live electrical box, your tendency is to retract your arm. Very quickly.
But even 120 or 240 volts won't jump across very much air, like, essentially, none.
Compare that to the 100,000+ volts that are carried by the high-tension lines at the top of int[er|ra]state transmission lines -- that's enough voltage to arc across many inches of air without any trouble at all.
So why do we use high voltage at all, why can't we just use low voltage everywhere and be safer?
That's where the magic of the power equation (Power (watts) = Volts * Amps) comes in. But that's for another discussion.
But, if you don’t read the whole article, do read this tidbit.
“ ...little use by educators of the wind/sound electrical analogy:
AIR is a physical substance.
SOUND is a wave that propagates rapidly through a volume of air.
WIND is a flowing motion of air already present.
ELECTRIC CHARGES are a physical substance.
ELECTRIC ENERGY is a wave that travels via a column of charge.
ELECTRIC CURRENT is a flowing motion of the charge already present.
The confusion between charge-flow and energy-flow is similar to confusion between wind versus sound. Do you know that sound is not wind? To believe that electrons flow at the speed of light is similar to believing that air must travel at 720mph out of your mouth to distant ears. “
Try the finished versions instead:
List of electricity articles
List of typical electricity misconceptions
I wonder, is there any resource online that explains electricity properly in a "for dummies" way? I'd be interested in going through it and seeing what surprises me.
This is however the tip of the iceberg. The real mystery is how those electrons and protons feel each other. They don't bump into each other like atoms in the air, they interact via magnetic field - a mysterious medium that magically appears around charged particles and alters their trajectories. It's the same magnetic field that surrounds bar magnets. Rumors are magnetic field is made of photons, but nobody has been able to see or catch those photons, so they have been renamed into virtual photons. Those special photons don't really exist, but still interact with charges.
Is it any more mysterious then how our planet 'feels' the presence of the Sun, through the gravitational force, despite being 150,000,000 kilometers away?
That's why I still don't understand gravitation, at all. I don't care that we can calculate something. That doesn't tell me what is actually happening.
Electrons = Water molecules
Battery = Water tank
Wire = Pipe
Load = Water mill
Voltage difference = How high tank is from water mill
Amps = Amount of water molecules flowing through pipe
Resistor = Pipe with sand
Water is flowing out of the hose at some rate. If you put your thumb over the end of the hose, you can create a stream of water (of less volume) that shoots out a farther distance because of increased pressure (you can feel this pressure increase in your thumb).
Think of amps as the volume of water, and voltage as the pressure. Power is voltage times current, or pressure times volume of water.
You could squirt a stream of water many feet (raising the voltage), but it's not a very large quantity of water (amps). Conversely, with your thumb off the end of the hose, the pressure (volts) isn't very high (it just flows out at whatever your tap pressure is), but the volume of water is significant (amps).
Curious whether that is any clearer of an analogy?
Potential energy due to gravity is mgh. A pump adds more force to g. A tower increases h.
What's nice about the pump is that it removes the special spatial directionality of gravity. In electricity, Earth is a voltage point-of- reference but not a spatial directional reference for computing forces.
Electrons flow in metals, but inside most non-metals, free electrons don't exist. For example:
Protons flow in acids. But chemists call protons "+H ions"
+Na and -Cl flow in salt water (and in damp ground.)
-OH negative ions flow in alkaline electrolytes
-OH, protons, +Na, -Cl, +K, and all sorts of charged molecules flow inside human bodies. (When you receive a shock, no electrons flowed through your body.)
Electrons and positive ions flow in spark-plasma, lightning and fluorescent tubes.
In liquid metals, electrons flow one way and positive metal ions flow the other. (So, only solid metal wires are purely electron-conductors.)
In moving wires, both protons and electrons are moving. But since the amperes are the difference between electron and proton flows, the motion of the metal doesn't create any current. (Note that electric current in wires isn't a flow of electrons, instead it's the difference between electron-flow and proton-flow.)
Also, look at the currents in salt water: positives flow one way, and negatives go backwards past them, in the same conductor. What then is the "true" direction of the current?
Though I don't think protons get transferred over a wire.
I agree with the top parent comment, I wish we had gotten the charge of electrons correct. I remember bandgap diagrams being confusing too because electrons basically roll "uphill" and felt like it would be easier to understand if we just called them positive.
Free electrons can temporarily occupy holes, then dislodge themselves and move on to the next place. But it will look like as if the holes are moving from one place to another.
D = q1 / 4 pi R^2 describes the effect the first particle has on space at the location of the second particle. It relates the subject to the properties of its surrounding space.
And D = E epsilon of course tells you how those quantities relate to each other. It's basically the verb. Together these describe how two stationary particles interact with each other electrically. They link the subject and object together. Think of it as subject -> verb -> object.
The motivation for all of is to decouple things so we can reason about them independently.
Hopefully that's lucid and intuitive?
E alone cannot describe fully state of dielectric, and B alone cannot fully describe state of magnetic medium. We need additional concepts, either charge/current densities, or polarization/magnetization, or D/H, in that order of importance.
In modern understanding, D and H are auxiliary concepts that are useful mainly in special but important cases they were historically devised for. Let's take D for example. If free charge is absent, Maxwell's equations imply very nice equation div D = 0. The equation for E is more complicated (includes bound charge density that is hard to measure, hard to relate to other things in the model and so is usually preferred to be ignored).
If in addition the medium is linear (a special but important case), D is a simple linear function of E ( there is no such simple relation to charge density or current density) so things such as the concept of EM energy in medium is possible, and wave propagation in crystals can be analyzed most elegantly. Sure, all could be analyzed in terms of E and rho and j which would be more "physical" but it is not the most elegant way to do it. It is like in mechanics: we can analyze complicated systems with constraints by writing down many equations involving constraint forces, but there are easier methods such as the Lagrangian.
The reason for the introduction of D is that even though a medium may have no net charge, it's still made from protons and electrons, meaning the charge density will be nonzero. We call this the density of 'bound' charges ρ_b.
The medium is often modelled as consisting of tiny dipoles. If left to their own devices, the dipoles tend to align in such a way that the generated field largely cancels out.
Now, let's add additional charges via a density of 'free' charges ρ_f, yielding a total charge density ρ = ρ_f + ρ_b.
The bound charges will respond to the presence of the free charges, and the field they generate will no longer cancel out. We call this field -P, with P the electric polarization (the negative sign comes in through its definition as the dipole moment density of the dipole model).
Defining the electric displacement field as D = E + P, Gauss's law
div(E) = ρ
can be decomposed into
div(D) = ρ_f
div(P) = -ρ_b
In many cases, the response of the medium will be approximately linear, and polarization will be proportional to the field generated by the free charges, P = η·D. Note that the definition of P was such that for positive η, the actual field will be opposing D.
Equivalently, we can consider the response linear in the total field, P = χ·E if we introduce the electric susceptibility χ = η/(1-η).
For the displacement field, we get
D = E + P = (1 + χ)·E = ε·E
with ε the permittivity.
What's the point, you may ask? Simplification, as we can now just measure the linear response of the medium, instead of having to figure out the microscopic distribution of bound charges.
div(E) = ρ = ρ_f + ρ_b
div(D) = ρ_f
Admittedly, things get muddled because the distinction E vs D does double duty: We also associate E with (specific) forces, and D with fluxes. Depending on your system of units, this necessitates the introduction of a conversion factor.
Quote: "Scuff across a rug, and you charge your body to several thousand volts." Pardon me?
Further down: "Can an object have a certain voltage? No. Why not?" How does that fly with the above statement?
These articles are exactly the confusing non-pedagogical and partially straight out incorrect nonsense that the author criticises in other works.
The actual completed articles were written years later, many were even inspected/corrected by the phys-L group of college physics educators. http://amasci.com/ele-edu.html
I'm trying to read up on it because I realized my knowledge about electricity is very basic (only first year physics lecture on electricity & Maxwell's equations).
He made the proton positive, and the electrons negative. But this mistake became a historical embarrassment, but ultimately stuck, because the world was too entrenched in it.
Instead, he should’ve made the proton as negative, and the electron as positive. Intuitively, this may have helped people understand how electricity flows better.
An alien extraterrestrial society in a distant galaxy would probably be wondering why we have our electricity signs all backwards.
Such as: why must we disconnect the negative cable from our car battery first?
One, electrical energy does not flow from cathode to anode. Nor does it go the other way. The energy goes down both wires, from source to load.
Two, it's an arbitrary decision if you want to talk about negative charges going east, or positive charges going west. They're equivalent when talking about a net-neutral wire.
There are a lot of symmetries in the world that we break by arbitrary convention. The polarity of subatomic particles, the right-hand rule used in vector mathematics, the way bolts are threaded.
The alien society might just use a "left-hand rule" for their magnetism and vector operations, and have clocks that turn opposite of ours (which probably means their planet orbits the opposite way?)
As far as car batteries go, the reason to disconnect the (–) first is because it's almost always* the chassis ground. If you were to work on an ancient Volkswagen, then you'd be told to disconnect the (+) cable first. Disconnecting the other terminal first is more dangerous; your wrench is a perfect short circuiting tool!
* And the reason we all use negative for chassis ground has to do with galvanic corrosion, I think?
And it doesn't even "do gown" "the wires" depending on what you mean by that. The energy flux is IIRC the product of E and B fields, which is non-zero only outside the wires.
The wires, in a sense, only acts as a rough guide for the energy, which itself is transmitted through the air/non-conducting surrounding space, and (importantly for some applications) enters the load from its "sides", from the non-conducting space around it, not through the wires.
Developing the idea, I have a similar multiple definitions problem, in a much smaller context, with the word “prescription”.
In the UK it means all of: a doctor’s idea of what medicine to give to a patient, a piece of paper with that written on it, and the medicine itself.
I got thoroughly confused when I went to collect a prescription from a pharmacy and was told “it’s (still) over at the surgery”. It wasn’t, or rather, it was. But we were talking about different prescriptions.
Anyone else have these (pedantic?) confusions?
“Extrusion” is a process as well as the object resulting from that process.
“By referencing the meter and adjusting the metering valve during extrusion, we can create a precisely meter long extrusion.”
Micrometer is a unit of measurement and measurement device that measures in that range, but often measures in thousands of an inch, which are commonly called “mills”, which is also the act of a type of machining and the name of the machinery that does it as well as the name of a common type of cutting tool that goes into that machine.
“Put an end mill in the mill and mill off five mills.”
There is "meter" and there is "metre".
> “Put an end mill in the mill and mill off five mills.”
Probability on Trees and Networks
by Russell Lyons and Yuval Peres
As a comment on the style of "Why is electricity so hard to understand?", mathematicians get inundated with crank missives claiming simpler proofs of Fermat's Last Theorem, and many other hard problems. On one hand we try not to judge the delusion, as it takes a certain amount of delusion for any of us to find the confidence to overturn old ideas. Yet there's a balance here. With cell phones, the ability to self-rescue in the woods has gotten lost. Even the most delusional serious mathematician knows how to "self-rescue". Part of commanding one's work is understanding it in context, and to see how one might critique it, more incisively than any potential reader. This is not unique to math; "writer's block" is a writer losing control of this balance, just as insanity is anyone losing control of their inner chaos.
"Why is electricity so hard to understand?" is indulgent; it doesn't even try not to read like a crank missive.
I often reply to crank missives with advice on how not to be immediately coded as such. The world would be more fun if we were unable to tell the crazies apart from everyone else. Alas this advice rarely takes.
It tells you that it's not an article. It's a crapload of unedited notes I scribbled down in random order on little scraps of paper back in 1988. You complain it has no style? IT'S NOT FOR OTHERS TO READ! (I keep hiding the file to avoid this problem, changing the filename, but people keep finding it and re-posting it here.)
Since 1988, the vast unedited garbage-pile I later used to write some actual articles, see the index: http://amasci.com/ele-edu.html THOSE I invite everyone to critique.
Some of them tend to enrage people, because:
- Problems worthy of attack,
prove their worth by fighting back.
- Piet Hein.
I find that people having long-standing physics misconceptions will fight like fury to preserve them against change. In the present case, my misconceptions-list was inspected by the Phys-L educators forum in the 1990s, for comment and critique (and numerous flaws repaired. But NOTE of those changes appear in whyhard2.html)
> with advice on how not to be immediately
My advice: read the friggin' first line! Here, I'll edit it to make it even clearer:
"BELOW are my original, very crude disorganized and totally unedited 1986-1989 notes and "raw data" collected on little scraps of paper for...
I am not being sarcastic!
You see, I've had the same thoughts (about the many paradoxes in the existing knowledge of electricity) for a long, long time!
This article goes a long way towards challenging the "status quo" with respect to what is currently known and/or popularly believed about electricity...
It is well worth a reads and many re-reads, both now and in the future...
My absolute favorite article on HN, thus far!
Some excellent links!
But, you've always ran an excellent website since day one, a long time ago, to be sure!
Fun historical fact(!): One of the first articles I posted to HN a long time ago -- was your article on hand-drawn holograms!
I wouldn't have posted that... unless I thought you were on to some deeper principle, some deeper truth, something... in other words, there was something there...
Anyway, if you would like to connect via email and/or LinkedIn, I'm available at email@example.com and/or www.linkedin.com/in/peter-sherman-a6107a5
I think you'd find me a fascinating guy of your caliber...
Of course, if you'd rather not, and value your privacy, then I respect that too...
Now it has clicked I intuitively understand how things like bypass capacitors work. But I don't think I could explain it well enough to teach it. It seems like it it doesn't click for you you'll never be able to do electronics.
I noticed in The Art of Electronics they don't capitalise ac and dc. I wonder if that is to escape the popular ideas of the capitalised AC and DC? I looked but couldn't find an explanation in the book.
I think he does an excellent job of explaining why it's so hard to explain this type of thing.
Has somebody a good visual analogy for this in another medium?
I mean I know that this is a case but I can not visualize the energy flowing on both sides out of the source with the medium only moving out on one side.
I will try for myself:
Say I pump a lot of water in a circle by moving a pump by hand. I put some energy into the system. By pumping I push water molecues out one side of the pump and pulling them in on the other side. That creates a pressure difference inside the water. Even if I pump the water really slow, that pressure difference propagte with the speed of sound through the water. That pressure difference is positive one the one side of the pump (water is pushed) and negative on the other side (water is pulled). Somewhere on the other side of the pipe circle the pressure differences meet cancel each other out. So the pressure difference is the energy moving through the system in both directions. But the water itself only moves in one direction.
But now we have two kinds if energy in the system. The pressure wave and the kinetic energy of the water.
If I keep pumping the water will speed up faster and faster. I guess that's the analog to a glowing wire.
But if a put a turbine into the water the flow of water will be slowed down because the kinetic energy of the water is extracted by the turbine.
Now if the water is at rest and the turbine as well and I now start pumping the pressure difference will flow in both directions to the turbine. It will start spinning as soon as the pressure differences meet there.
If the turbine is not opposite to the pump the pressure differences will take different amounts of time to reach it. But the turbine will already start moving when hit by the first pressure difference by absorbing it the (pressure wave stops there) and then latter be hit by opposite pressure difference and move again.
So far correct?
So in an ideal system the water would not move at all but only the pressure difference would propagate and be consumed by the turbine.
But that would mean that the turbine energy leaves the system completely -> the turbine does not even turn because it's energy is 100% extracted by it's consumer.
So in this example flowing water always represents some kind of loss/inefficency.
The goal would be to maximize the pressure difference to propagate but the minimze the water flowing.
Is this how you could explain alternating current for transportation of energy?
Imagine that for some insane reason, you set up a pipe underwater. On one end of the pipe you put a pump that pushes water into the pipe. At the other end of the pipe, you put a vacuum that sucks water out. In the middle of it, you put a turbine that powers a lightbulb. When you turn it on, energy flows from the pump to the turbine because the pump pushes the water. Energy also flows from the vacuum to the turbine because it sucks water out.
Batteries work like that, but with electrons as the medium. Negatively charged particles repel electrons, and positively charged ones attract it. So when you make a circuit, the negative terminal pushes electrons away from it and the positive terminal pulls them, resulting in both sides giving energy to the load.
> Is this how you could explain alternating current for transportation of energy?
This part I don't grasp super well, but I'll take a stab. It's a higher level thing. Resistive losses are relative to the current squared. So you want low current. But you need to deliver a lot of power, so you have to raise the voltage. Normal people's homes can't handle 200,000V power, so you have to convert it back to a lower voltage before you put it in people's homes. The cheapest/easiest way to do that is with a transformer, which requires a varying current (i.e. no DC).
So, when energy moves from a battery and flows outwards on both wires, also the "medium" is flowing inwards on one wire, outwards on the other.
An electric circuit is like a leather drive-belt. A generator is like a pulley.
When we force the pulley to turn, the entire drive-belt must turn also. The electrons are the leather, and they go slowly in a circle. But the "work" or the "horsepower" zips instantly along the belt, moving fast as the belt moves slow.
And, if we WIGGLE the first pulley, the belt also wiggles back and forth. Yet the "work" only flys outwards from the pulley, zooming off into the distance, regardless of which way the belt is turning.
It seems like a reasonable model for DC. For AC you have to account for the repeated change in direction, which just looks odd in a hydraulic system because the medium has so much inertia.
Enjoy the talk!
> ELECTRIC ENERGY is a wave that travels via a column of charge.
what's a "column of charge", and where could i read more about those (preferably online)? i found the term ungoogle-able – i keep getting stuff with "coulomb" instead. (and i'm assuming it's not a typo)
In other words, all metals are always full of electron-fluid. They're like plumbing pipes, but pipes which are pre-filled with water, with no bubbles allowed. During an electric current, it's the wires' own electrons which begin flowing. (A long thin column of copper is always a long thin column of movable electric charge. So, hook it in a circle, and that creates an invisible "electron flywheel.")
See the completed article: http://amasci.com/miscon/elect.html, a big list of common misconceptions.
It's an analogy, providing a correspondence between a column of fluid and a column of charge (the 'electric fluid').
Abstract concepts that you can’t touch or see are hard.