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Why is electricity so hard to understand? (1989)

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Re: Why is electricity so hard to understand? (1989)

#161

Post by delinka »

roel_v wrote: post #143

Maybe this is the right occasion to re-ask a question I asked some years ago on stack exchange, but (despite several people trying their best to explain) still failed to understand the answer to. So: does electricity have 'mass'? What I mean is, when current flows, is there a transfer of electrons (or something else) from the power source to whatever it is send to? And is there a difference between AC and DC? The con…

Yes, there is a transfer of electrons from one place to another. It's not to the thing that does work, but through the thing that does work.

With a battery (DC/direct current), there's a surplus of electrons available at the negative end, a deficit at the positive end. The electrons flow through a circuit (from - to +) to perform work.

With AC/alternating current, the electrons flow in one direction, then the reverse direction several times per second. The purpose of this is to push energy further down transmission lines with less loss. Pushing DC from a plant to everyone's houses is very lossy.

Do electrons have mass? Yes. Does the circuit or device increase in mass when current is involved? No. You're actually not introducing additional electrons into the circuitry. The conductors and semiconductors already have electrons on the outsides of their atoms. We introduced an electron at one end, it hops onto an atom, pushing an existing electron over to the next atom and so on. It's the movement that produces "energy" and allows work to be performed.

Strictly speaking, you can hold extra electrons for short periods of time in capacitors, but the mass is so small as to be negligible.

Re: Why is electricity so hard to understand? (1989)

#162

Post by seiferteric »

thisrod wrote: post #157
seiferteric wrote: post #49

Earlier quoted context omitted.

Not really sure I like that link. He seems to suggest that capacitors store "energy" instead of charge, which is just as ambiguous really. It's not like there is some sort of energy particle either. Of course what's really happening is that you are creating an electric potential between two plates. It's true that the net charge is the same, but you are moving electrons from one plate and forcing them (doing work) int…

> water does not attract other water in any way Um ... once we've cleared up all the misconceptions about electricity, we might want to move on to this other thing called gravity :-) The usual reason that people are mislead by "water" analogies—more precisely, the analogy between height and electric potential—is because they misunderstood gravity to start with. If you start by writing Newton's law and Coulomb's law s…

Yes as I said in a later comment of course cohesion and gravity exist, but they are not relevant in this analogy.

Re: Why is electricity so hard to understand? (1989)

#163

Post by wbeaty »

feedjoelpie wrote: post #44
overcast wrote: post #27

The real question is, why is this website so hard to understand? Publishing what looks like someones personal notebook isn't helping the cause here.

Poor selection of link. Fortunately the author saw us and pointed us toward the articles instead of the raw notes: http://amasci.com/miscon/whyhard1.html#def

For those who don't like raw notes, why not read the finished articles instead?

The index to the large collection is here: http://amasci.com/ele-edu.html

Re: Why is electricity so hard to understand? (1989)

#164

Post by wbeaty »

hyperliner wrote: post #21

Whaaat? Electricity does not flow at the speed of light? OH THE HUMANITY!!!!

When I step into the pond, the ENTIRE WATER LEVEL RISES AT THE SAME TIME! Water must travel instantly?

So, a hydro dam is actually a method for sucking the energy out of the entire surface of a lake, all at the same time! (Actually the pressure-waves travel at the speed of sound in water, a few thousand MPH.) It doesn't happen instantly, but damn close.

Re: Why is electricity so hard to understand? (1989)

#165

Post by wbeaty »

LgWoodenBadger wrote: post #34

What's the difference between ionized hydrogen and electricity?

Hydrogen gas is insulating matter. Ionized hydrogen is conductive matter.

Too bad we don't have metallic hydrogen. It would be a solid conductor, just like any other metal.

"Conductor" actually means "contains mobile charges." Conductor doesn't mean "a hollow pipe which electricity flows through." Conductors are more like long, narrow ponds. They're made of 'electric fluid,' so if we have a ring-shaped pond, we can push the water along so it starts moving in a complete circuit, like a drive-belt.

Re: Why is electricity so hard to understand? (1989)

#166

Post by CamperBob2 »

wbeaty wrote: post #160
CamperBob2 wrote: post #127

Earlier quoted context omitted.

But inches are an abstract measurement of distance. Electrons are a thing. (Well, depending on who you ask... no one has ever seen one, and some people have claimed half-jokingly there's only one electron in the entire universe: https://en.wikipedia.org/wiki/One-electron_universe .)

So, you're saying that capacitors store electrons?! Debunking this particular conception was the whole point of my capacitor article http://amasci.com/emotor/cap1.html Capacitors "store" electrons, like springs "store" steel, or rubber bands "store" rubber. A charged capacitor has exactly the same number of electrons as an "uncharged" capacitor. When "charging" a capacitor, charge is forced into one terminal, and exa…

Capacitors store joules, not coulombs.

Fair enough -- a two-terminal capacitor that stored electrons supplied via one terminal could be charged without drawing any corresponding current at the other, violating Kirchoff. I do like your water-filled sphere analogy, and I agree that the word "charge" is an overloaded term.

But what would you say is happening at the top electrode of a Van de Graaff generator? It represents a reservoir of stored (positive) charge. Electrons have been physically moved outside the device, and we use the same language to describe this process -- that of capacitance.

I guess the argument would be that the objects in the room constitute the other terminal of the capacitor, with the intervening empty space forming the "dielectric," and that the electrons removed from the sphere aren't associated with the sphere at all, but have just been moved from one region of the dielectric to another?

Re: Why is electricity so hard to understand? (1989)

#167

Post by wbeaty »

syncsynchalt wrote: post #94

All those words and it doesn't even entertain my favorite if-i-had-a-time-machine scenario: EE would be a bit easier if Franklin had swapped positive and negative.

Sure it does. You just have to look at the list of articles, not the giant pile of random notes.

BEN FRANKLIN SHOULD HAVE SAID ELECTRONS ARE POSITIVE? Wrong. http://amasci.com/miscon/eleca.html#frkel

EE would be much HARDER if Franklin had swapped positive and negative, since then our confusion wouldn't lead us to shatteing our own misconceptions. We'd never sit down and figure out what "conventional current" actually is. No, it's not backwards. And no, electricity is not made of electrons. In acids, the electric current is entirely a flow of protons. In dirt, oceans, and human bodies the current is at least two separate flows: clouds of positive ions passing forwards through clouds of negative ions travelling backwards. With two opposite charge carriers, what then is the "true" direction of electric current? What if there are five: +Na, +K, +H, -OH, -CL ?

Cute notion: Ben Franklin's kite string was an acidic conductor, a piece of twine which becomes insulating in dry conditions, so it's an electrolyte. And acid conductors have mobile +H ions to carry the current. (What's a hydrogen atom, with one missing electron?)

In other words, Ben Franklin's kite string is a Proton Conductor.

SO HE GOT THE DIRECTION RIGHT!!!!

:)

He only was wrong in the case of metal wires. In his day, a typical "conductor" was a small boy hired to hang from silk ropes, to connect the Leyden Jar to the "Electrical Machine." Or rather than commoners, sometimes they used chains of Elizabethan royalty, all standing upon insulating stools.

Re: Why is electricity so hard to understand? (1989)

#168

Post by wbeaty »

ambrop7 wrote: post #91
seiferteric wrote: post #49

Earlier quoted context omitted.

Not really sure I like that link. He seems to suggest that capacitors store "energy" instead of charge, which is just as ambiguous really. It's not like there is some sort of energy particle either. Of course what's really happening is that you are creating an electric potential between two plates. It's true that the net charge is the same, but you are moving electrons from one plate and forcing them (doing work) int…

My water analogy for a capacitor is a piston with pipes attached to both ends, with a spring system that pushes the piston towards the center position. Is that not a mathematically correct equivalent? (in an idealized system with no water resistance/inertia and disregarding that the piston is of fixed length - not that real capacitors have zero resistence, inductance or can store infinite charge)

That's what I started out with! Fill the entire universe with solid rock (since air and vacuum are insulating.) Bore out a cylinder, fill it with water (electricity), and add a piston and spring. Wires are water-channels added to either end.

But note that, if we use a constant-force spring, then the voltage remains the same until just before the "capacitor" is totally discharged. So, it acts like a battery! To get a "capacitor," the spring must have an unchanging spring-constant, so that the potential-difference rises in proportion to how much water has been pumped from one terminal to the other.

Re: Why is electricity so hard to understand? (1989)

#169

Post by wbeaty »

javajosh wrote: post #140
ambrop7 wrote: post #91

Earlier quoted context omitted.

My water analogy for a capacitor is a piston with pipes attached to both ends, with a spring system that pushes the piston towards the center position. Is that not a mathematically correct equivalent? (in an idealized system with no water resistance/inertia and disregarding that the piston is of fixed length - not that real capacitors have zero resistence, inductance or can store infinite charge)

From an energetic standpoint, a capacitor is something that takes a trickle over a long time, and releases a flood over a short time. So it would be a water tower with a small input and a large gated output.

But a water tower only has one terminal. A better "capacitor" would be a pair of water towers side by side.

To "charge" this double-water-tower capacitor, pump some water from one to the other. And, when the water-tower capacitor is entirely "discharged," the towers both have the same water level inside. (As with a real capacitor, the total amount of water never changes.)

Re: Why is electricity so hard to understand? (1989)

#170

Post by wbeaty »

k__ wrote: post #24
notalaser wrote: post #16

I think more than half the time I spent earning my EE degree has been spent unlearning the intuitive (but wrong) things that I was liberally taught. I was fortunate enough to have an exceptional Physics teacher in high school, who managed to avoid a lot of the bullshit that less fortunate students were fed; sadly, I compensated that with some of my own (misguided) self-study. This experience also taught me to activel…

I got it taught about 3 or 4 times, and every time I understood it less. In middle school they told me, it's electrons moving at the speed of light through a conductor. In high school they told me, no no, they don't move at the speed of light, just when one electron enters the conductor, another one on the other side will leave the conductor, like with peas in a straw. And this enter/leaf is at the speed of light. At…

It actually is the electrons. But they never touch each other. Instead they push upon each other across empty space, by using e-fields and b-fields.

If there wasn't any chain of electrons inside the conductor, then the EM fields would just fly off into space, like with a transmitting antenna.

Wires can guide the EM energy because each electron can push the next one in sequence. But also, one electron doesn't just push on the next one. Instead, it pushes on a huge number of electrons far upstream and down the long chain of mobile charges going off into the distance. That's why the EM energy can "leapfrog" across the movable charges, at the speed of light. If each electron could only push upon its nearest neighbor, then electrical energy would travel at about the speed of sound.

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