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I live in Brazil, our residential electrical outlets are 127 VRms, 60 Hz.

So if I were to plug a fan (AC motor, forget anything DC) into the socket and then I were to "ride an electron" that's at the interface socket/fan cable what would I see?

EDIT to make my question more explicit: A car very simple converts the energy from the chemical bonds into kinetic energy.

What is the "chemical bond" of the power outlet?

Does the electromagnetic field get a tiny bit weaker/"consumed" by the AC motor?

The electron can't lose mass. Can't lose charge. Can't travel more in one direction than the other. Is it something in the electrical-magnetic wave permeating the wires? Does it have something to do on a quantic level?

PS: I did 4 years of chem engineering grad and transferred to electrical engineering (currently at the 4th year with an "focus" on computer engineering), so I have good theoretical concepts of power, energy, voltage, current, transformers, generators/motors, thermodynamics, ..., and some knowledge of basic quantum physics/chemistry.

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  • \$\begingroup\$ Well, power is voltage * current. But maybe it would help to consider the potential energy of an electron as it moves through an electric field. The direction of decreasing potential energy is the one that results in power being delivered by the utility company to your home. If you force the electrons to move in the opposite direction, so that their potential energy is increasing, then you must have a generator onsite, delivering energy to the grid. \$\endgroup\$ – mkeith Feb 1 '18 at 4:31
  • \$\begingroup\$ Welcome to EE.SE. The power line is not losing anything, though under heavy loads it heats up at the expensive of some electrons. It is merely a transport mechanism for electrons, which must loop through your load (whatever that is) and return back to the source to complete the circuit. Just like a battery and a light bulb, except it is AC not DC. \$\endgroup\$ – Sparky256 Feb 1 '18 at 4:38
  • \$\begingroup\$ If you think of the electrons as being fully deterministic entities that hop along from atom to atom, they don't actually move very far during a 60 Hz cycle. The utility company is not selling you electrons. They are selling you power. It is really better to think in Volts and Amperes, or think about fields. \$\endgroup\$ – mkeith Feb 1 '18 at 5:11
  • \$\begingroup\$ As part of your PS - you should add magnetism and electro-magnetism. \$\endgroup\$ – Solar Mike Feb 1 '18 at 6:16
  • \$\begingroup\$ conservation of energy...you cannot create it nor destroy it but you cant transform it. You are converting it from an electrical form to a mechanical form. You are dumping energy into the moving parts which are pushed back on by friction, creating heat. So you are creating heat and motion. Just like the gas in the gas tank. Heat and motion. \$\endgroup\$ – old_timer Feb 1 '18 at 10:27
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Does the electromagnetic field get a tiny bit weaker/"consumed" by the AC motor?

Yes, exactly right.

To simplify, imagine a single 2-wire AC circuit (not complicated 3-phase.)

First, the utility company dynamo will charge two wires opposite, like a very long capacitor. One wire is temporarily positive, the other negative. Next, your motor inside your washing machine will "discharge" this long capacitor, taking some energy from the e-field which exists in the space between the long wires. (The dynamo increases the voltage between the wires, and simultaneously, the motor slightly the voltage.) The dynamo "charges" the capacitor with energy, while the motor "discharges" it.

But also, the utility company's dynamo will create a current in the entire circuit, including the miles-long wires and also inside the AC motor coil. The entire circuit stores energy as a magnetic field (it's a 1-turn inductor.) The dynamo increases the current in the circuit, while the motor simultaneously decreases it slightly. The dynamo "charges" the inductor with magnetic energy, while the motor "discharges" it.

Together, the above two effects are allowing electro-plus-magnetic energy to race along the circuit, flowing from dynamo to motor. The circuit behaves as an inductor-capacitor ...also called a "transmission line."

In other words, the dynamo injects EM energy into the entire system. Then the distant motor withdraws energy from the entire system. The EM field-energy then flows across the system at the speed of light. (But electrons themselves travel slowly.) Electrical energy is wave-energy, while the electrons inside the wires are the "medium" which guides the waves. (Don't forget that sound-waves travel fast across great distances, while the air-molecules themselves just vibrate slightly. Waves versus medium.)

Here's the secret to understanding energy in circuits: all circuits are EM waveguides. They are radio transmission lines, even when the transmission frequency is 60Hz, and even when the frequency is DC or 0Hz. In other words, transmission lines have no lower limit to frequency. The same mathematics which applies at 1MHz also applies at 1Hz and at DC. In engineering classes, many of us miss the fact that our fields/waves textbook wasn't describing RF transmission lines ...it was describing all transmission lines, including 60Hz power grid, and including the conductors inside a DC flashlight.

Note that with car engines and drive shafts, the energy travels as sound-energy of very low frequency. The metal atoms in the drive-shaft are the "medium" for this mechanical/acoustic energy-flow. The metal atoms don't flow along the drive-shaft! But the kinetic energy does flow along the drive shaft, going from motor to wheels (and ...it travels at the speed of sound in steel!)

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  • \$\begingroup\$ This is an excellent answer. Power can be transmitted through vacuum in the form of electromagnetic waves, ie propagating fields, ie photons, in other words light. Copper wires act as waveguides and allow us to guide the energy where we want it, by the same mechanism that a mirror uses to reflect light. \$\endgroup\$ – peufeu Feb 18 '18 at 0:00
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Power line doesn't lose any thing. It electromagnetically makes an energy transfer link between the source and load. Think about the shaft and gears between the car engine and the tires, same thing, except the transfer medium.

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** “A day In the life as an electron”**

Where Have you been all day?

Conducting as usual like all the other copper particles inside this electrical interface socket. My life is pretty stable here but it’s so crowded, I don’t move as fast as you think. You must have me confused with the waves travel thru me at the speed of light. Back and forth, sixty times a second. Sometime it gets “exciting” when someone unplugs a vacuum cleaner still running and this 4000+K burning arc starts and some of my friends escaped.

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The electron moves back and forth, probably an astonishingly short distance, 60 times a second.

The question I think you're asking is, (a) what makes it move? and (b) how does that movement do any useful work?


(a) It moves because an electric field pushes it, or pulls it, alternately. That electric field comes from upstream electrons crowding towards it, each in turn pushed by the electric field, all the way back to the generator. Or being pulled away from it, in the other half cycle.

Line up a row of pennies with 1mm between them, and push the left hand one 10mm towards the others. You'll see that though each penny moves a few mm, the wavefront of increased money density has moved 100mm or more. That rate is limited by the speed of sound in pennies. (Yes it's crude, pennies only repel each other by physical contact, while identical charges repel each other by an electric field)

So, though each electron moves at a relatively slow "drift velocity" the energy (transmitted by electric field) propagates at the speed of light (not in vacuo, but slower thanks to materials properties) - typically 0.7*C.


(b) It loses energy in two ways. First, it bumps into the atoms in the wire, transmitting kinetic energy to them, making them vibrate. In your fan, this is wasted energy; in a stove or lampbulb, it heats the wire - to about 300K in the latter case, emitting light.

Secondly, as a moving charge, it generates a magnetic field. If there are nearby conductors, that magnetic field induces current in those conductors, which generate their own magnetic field, and generates a force between them. The strength of that magnetic field retards the electron (this is the basis of inductance). If the second conductors are free to move in the direction of that force, they will, turning the fan blades. Force * distance = energy - this energy is drawn (via the magnetic field) from the electron's motion. (Of course, rather than generating magnetic field in a movable set of conductors, some motors use movable permanent magnets instead. Or fixed magnets and movable conductors, etc)


If you can see the link between electron flow and mechanical motion, you also need to understand that this process is perfectly reversible, and ni fact the generator produces the "push" aka electro-motive force (EMF), aka voltage, by the same process in reverse.

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Your fan affects the movement of electrons in the way that slows down the turbine producing electricity that powers up your house. The turbine thus consumes more steam, which is replenished by burning more fuel.

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I think it would be easier to ask about where electrical "energy" comes from first, then look into power later.

In the Beginning ...

Physical laws binding energy conservation will help us. Energy can't be created, nor destroyed. Electrical energy is just obtained from one form (solar, kinetic energy from wind, turbine rotation, nuclear reactions, etc). This energy source provides the necessary energy for electron movement which in turn sets up a potential difference (another way to measure the amount of energy a current stream may posses). So, to set up a pd of 12V, a current stream must have received energy, which can provide a voltage/ emf amounting to the 12V or more.

Our situation.

Right now you have an A.C fan so you probably know the theory behind A.C generators, which is simply some rotor, cutting though a magnetic field thereby generating a current stream (something like that). Which is simply energy conversion. This goes through transformers which build its potential difference for transmission. kind of like a frog preparing to leap so it's muscles contract before the jump. In this case, the electric current will be propelled through a transmission / distribution network to your fan, which has a motor and the motor uses the electrical energy it receives to rotate the fan (another conversion, wow). So the rate at which the electrical energy works for your fan is a measure of power.

So in essence, electrical energy has many sources, therefore so does power.

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