Your energy usage is measured by a recording watt-hour meter. This is an electric motor that has a field coil that establishes a magnetic field proportional the line voltage and a rotor field coil with the field strength proportional to the current into your house. It is possible to show that the speed of the rotor is then proportional to the power that is being used at any time. The speed of the rotor is calibrated by a magnet that is moved closer to or further from a disc that is driven by the rotor. The magnet generates eddy currents in the disk and that creates a resistance to turning in the disk with that resistance being proportional to the speed of the disk. The rotor is then geared to a counting mechanism that sums up the power as time goes by and the total energy used is indicated on dials that can be read from the face of the mirror. These days many such meters telemeter their reading and meter ID number back to the office and nobody even has to leave their coffee cup to read your meter. Incidently, the meter reads actual power used and not volt-amperes so if you have a load that is highly reactive and draws a lot of current with little of it in phase with the voltage you are only charged (directly that is) for that component of the current that is in phase with the voltage.
This might be a stupid question b/c i’m thinking too hard about what you said. If the current is 1800 amps, how does the wire in the cable not melt?
Yep, photons. I know you’re probably used to thinking of photons as light and radio, but photons are really the carriers of electromagnetic energy. As David Simmons said earlier, you can sure go ahead and ignore the photons–the math works just fine without them–but they’re there, nonetheless, quietly doing their work behind the scenes. In your electric kettle heating element example, the photons are exchanging energy between the moving charge electrons (which make up the electrical current in the element) and the electrons bound to atoms which make up the material of the element. In the process, the current electrons lose energy.
Current-carrying capacity if a given wire is determined by cross-sectional area and the resistivity of the material it’s made of. 14 AWG copper wire inside your walls can’t carry 1800 A, but a heavy copper transmission cable around an inch or so in diameter can. Actually, transmission cables are normally made of aluminum, but I wanted a common basis for comparison.
My example was illustrative only and was for a single two-wire line. Power is actually transmitted as 3-phase so the current for such a transmission line would be just over 1000 amp. The wires are BIG (1" or more in diameter) because the line loss needs to be as low as it can be made without excessive cable weight. The current density is low and the lines are well ventilated.
“Fools rush in…” QED has forgotten more about electricity than I know, (and I have forgotten nearly as much), but I think I can help you think about it differently.
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“What is it about a point that gives it a particular potential?” There’s no directly perceptible quality to grab hold of here; the best I can do is an analogy. Just as a mass generates a gravitational field, an electric charge generates an electric field. Every point in the gravitational field has a gravitational potential, and a second mass at any point experiences a force proportional to that potential. Every point in an electric field has an electric potential, and a second charge at any point experiences a force proportional to that potential. A fluid mass in a gravitational field will flow from high to low potential; charges in an electric field will flow from high to low potential.
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“Exactly what am I being charged for by the power company?” Electrons do not come into your house; they’re already there. The power company adds energy to the circuit, causing your electrons to flow. The more stuff you have plugged in, the more resistance your circuits put up, the more current you need, and the more power has to be applied to maintain the voltage and keep that current up. The meter in your home measures that ramp-up in power.
Oh yes there is. Colophon stated that he had scientific training in chemistry. So he presumeably knows about joules, coulombs, work, energy and all that jazz. There is no need to fiddle around with analogies and half measures.
I quote from Electrical Engineering Fundamentals, Corcoran and Kurtz, John Wiley & Sons., Chap. III
“A point in space possesses a potential of one volt if one joule of work is done upon a positive test charge of one coulomb in bringing the test charge from electrical infinity to that point.”
and
“Two points in space differ in potential by one volt if one joule of work is expended in moving a one coulomb test charge from the point with lower potential to the point with higher.”
That is as clear as potential can be made and should be understandable to anyone with scientific training.
In what way is that directly perceptible?
Well, it isn’t. But I think David Simmons is answering a different question that the one I think the OP asked, namely “what causes electric potential?” For the answer to that, you need to look into field theory, but in a nutshell, electric fields cause potential, which acts upon charged bodies. There’s a decent article here. One of the things it discusses is:
Now, you’re going to ask what an electric field is, and that’s where quantum field theory steps in. I don’t understand it well enough to explain it, however, but I don’t need to. It’s enough (at least for purposes of having a basic understanding of electricity) to know that electric fields supply the force needed to put charges in motion.
What’s this business about electrical infinity? I don’t get that.
And let me see if I have the theory of electrical energy transmission right:
At the power plant, fuel is used to move wires through a magnetic field, which gets the electrons moving. The electrons move slowly, but they run into each other, generating photons which move more or less along the wire. Some of the photons escape into space, and some collide with atoms in the wire and are converted to heat. When the energy reaches a stove element or a lightbulb, the photons again collide with atoms and are converted to heat or visible light.
Electrical infinity is the point at which the force computed by the Coulomb law, Q[sub]1[/sub]*Q[sub]2[/sub]/x[sup]2[/sup] approaches zero. The equation computes the force between two electrical charges, Q[sub]1[/sub]*Q[sub]2[/sub], and x is the distance between them. In short, the computation of the work done in order to find the value of the potential starts when the charges are so widely separated that the isn’t any force of one on the other and ends at the point whose potential is to be determined.
Close enough, except that in some cases, as in a motor, magnetic fields which interact to produce mechanical forces are the end result.
If we are limited to things that can be felt or tasted or smelled or heard we are indeed limited in our perceptions. What is perceptible in scientific matters to those with scientific training is somewhat expanded over that concept.
Electrical potential differences are certainly directly perceptible.
The formal definition of potential is:
potential = limit as Q[sub]t[/sub]---->0 of the ratio between work done on Q[sub]t[/sub] and Q[sub]t[/sub]
Colophon’s question was “1) What exactly is potential difference. A difference in potential between two points - well, duh - but what exactly is the potential at a given point? And how is this potential generated at a power plant?”
I think my post answers the first part of the question as asked. As to how a potential is generated. A potential is developed in a conductor when the magnetic field surrounding the conductor changes magnitude. A generator consists of a coil of wire being mechanically rotated in a magnetic field and that produces a potential difference between the two ends of the coil. In short, the mechanical work done on the coil moves charges,electrons, from one end of the coil to the other. This leaves an excess of charges at one end and a lack of charges at the other and work was done to produce this. This is strictly in accord with the explanation of potential difference in my answer. An electrical potential difference can also be establishec between two points by making use of electro-chemical reactions as in various types of batteries.
QED is doing an admirable job of addressing the root of the OP, in which Colophon is looking for an intuitive understanding of electricity. QED explained, and I’d like to re-emphasize, that electron flow is not what electricity is - the electric field is electricity. The field causes the electrons to flow. If you’re trying to understand, then, what the field really is, I think no one has a good understanding. We have mathematical models that work perfectly, but don’t peek behind the curtain. It’s also explained at a low level by quantum mechanics, which is just as precise but just as opaque to intuition.
To really understand how the field is important instead of electron flow, wrap your brain around this. In an electrical transmission line (coaxial cable, twin leads, that kind of thing), what determines the speed that the signal propagates down the line? Is it the speed that the electrons move in the conductors? No, not at all. It’s purely determined by the material that separates the conductors - the insulator, and how fast the field travels in that.
You may be confusing a theory with a hypothesis. In science, a well tested theory is accepted as fact and does not need to be couched in caveats. This is a common mistake of the anti-evolution crowd when they cry “But it’s only a THEORY”. Science never gets any better than the theory level.
Theory?hypothesis?Mirrors? Smoke?
We have a phenomenon which has never been seen,has no form,is odorless and ,so far as anyone knows,tasteless.
It has no weight,no volume and each month we pay some one for selling us what apparently "AIN’T.
It isn’t a single entity but is a combination of "named by necessity"factors.
We can see the multitude results of it’s application---------but the senses have never known it’s reality.
Call it what you will it’s still “The Theory of” in many texts.
'specially in mine!
Ol’ EZ

If you’re trying to understand, then, what the field really is, I think no one has a good understanding.
I’m not so sure about this. I think most people understand the concept of the force of gravity which causes objects with mass to fall to earth. The gravitational field is a force field that results in objects that have mass exerting forces on each other. An electric field is a force field in which objects having an electrical charge exert forces on each other. You can’t see the field and more than you can see the gravitaional field. But you can see its effect when pieces of paper stick to a comb after you have combed your hair, or a ballon sticks to the wall after you rub it on the carpet. If electric fields are esoteric mumbo-jumbo then so are gravitational fields. Both are force fields and the effects of both are directly observable in their effects on material objects.

Theory?hypothesis?Mirrors? Smoke?
Let’s not hijack this thread. If you want to discuss the scientific method, or what is meant by a hypothesis, a theory, or a scientific fact, it’s better to open a new thread specifically for that purpose. I’m sure you’d get lots of good responses.
Let’s not hijack this thread. If you want to discuss the scientific method, or what is meant by a hypothesis, a theory, or a scientific fact, it’s better to open a new thread specifically for that purpose. I’m sure you’d get lots of good responses.
You’re picking on the wrong guy----tell the one who brought up the matter of theory or “hyp-what the hell.”

In an electrical transmission line (coaxial cable, twin leads, that kind of thing), what determines the speed that the signal propagates down the line? Is it the speed that the electrons move in the conductors? No, not at all. It’s purely determined by the material that separates the conductors - the insulator, and how fast the field travels in that.
Exactly, although other factors do come into play. This fact is not lost on RF engineers, and is, in fact, critical to the proper design of both antennas and feedlines. The relevant term is velocity factor, and is the percentage of c that an electric signal propagates in a system. It’s used, among other things, to calculate wavelength fractions for various purposes such as element length, phase-matching harnesses for multiple antenna arrays, and feedline lengths. Here is a nice article about velocity factor with some happy diagrams and mathematical formulae, for those interested.

Q.E.D. will straighten me out but it helps to think of voltage as water pressure, and current as flow rate.
This isn’t a bad analogy, as far as it goes. It’s how my father (an EE for what was once Wagner Electric) first explained electricity me, in fact. It starts to break down when you try to explain inductance and other difficult concepts, but for helping someone with no clue about the nature of electricity to grasp the basic principles of and the relationships between voltage, resistance and current, it’s quite useful. In pont of fact, very similar principles are at work, and many of the formulae of basic electronics have remarkably similar analogs in the field of fluidics, which is the study and design of fluid circuitry. Inside your car’s automatic transmission sits a fluidic computer of sorts, which determines when and how the gears should be shifted. But, I digress…

Magnetism,e;ectricity,electronics,Etc—all measurable----all explainable--------but all still theoretical
Yeah, but so is the Earth being round. You could conduct an experiment like sailing/flying around the world that would support the theory that the Earth is round, but a sufficiently creative person could still imagine an alternative explanation.
My point is that all knowledge is “still theoretical” if you want to get technical about it. But at some point, there’s enough evidence in favor of a particular explanation that everyone with any sense accepts it as correct. The “theory” of how electricity works has been around for more than a century, and to the best of my knowledge we still haven’t found a single reason to think that it’s in need of drastic revision.