0
\$\begingroup\$

I used to think the negatively charged electrons traveled at near light speed to expend their charge in the form of heat at the load and then continue back to the positive source. Now I'm under the impression that the electrons are the medium which the energy travels and they actually don't travel very fast at all, they vibrate back and forth in the AC circuit. So what is the the name of the energy that does travel at near light speed and does the work at the load?

\$\endgroup\$
2
  • 1
    \$\begingroup\$ There isn't one. Your model of electricity is broken. \$\endgroup\$ Mar 28, 2017 at 3:27
  • \$\begingroup\$ "Electric energy"? \$\endgroup\$
    – user253751
    Mar 28, 2017 at 3:30

4 Answers 4

6
\$\begingroup\$

PING PONG BALLS

Electromagnetic fields move at the speed of light..

Electrons in a wire, are like a long, long pipe full of ping-pong balls.

You push one in one end and one pops out the other at almost the same time.. that's the speed of light part...

But it's not the same ball. The balls take a long time to move through.

Same with electricity:

You apply a negative voltage at one end of a wire.. electron goes in... field propagates to other end of the wire at the speed of light... electron pops out the other end.

WORK

The work part is how many electrons you push in (Current) times how hard you push them (Voltage).

\$\endgroup\$
5
  • \$\begingroup\$ Ok that makes sense. So now what about in the AC scenario where the same electrons keep getting pushed back and forth over the same resistor or load? Is it the same electrons that keep getting used over and over? Wouldn't they somehow lose their charge, or do they keep on working like the friction from a cloth wrapped around a pole and pulled back and forth to create friction? \$\endgroup\$ Mar 28, 2017 at 4:23
  • \$\begingroup\$ The ping-pong balls are inside a long circle of pipe. If you push one of them back and forth, all must move, but do ping-pong balls gradually escape from the pipe? Nope. And in the electrical analogy, we aren't required to only push the balls, also we can yank on one ball, and the balls all move in response, like a connected chain. In other words, the energy in circuits moves along both wires on its way between the battery and the distant light bulb. For another mental image, replace the circle of movable balls with a leather belt and two pulleys. Or, try a loop of water hose. \$\endgroup\$
    – wbeaty
    Mar 28, 2017 at 6:48
  • \$\begingroup\$ @wbeaty, yes but lets not make it more confusing that the OP can handle ;) \$\endgroup\$
    – Trevor_G
    Mar 28, 2017 at 12:33
  • \$\begingroup\$ Read Eric Heagan's 2nd question. The pingpong-pipe caused confusion, an improved analogy removes confusion: pingpong balls in a closed circular pipe. With a donut-shaped pipe, we can do AC. \$\endgroup\$
    – wbeaty
    Mar 28, 2017 at 22:15
  • \$\begingroup\$ @wbeaty hard to push a ball in the end of a closed circular pipe though. But you have a valid point. \$\endgroup\$
    – Trevor_G
    Mar 28, 2017 at 22:20
1
\$\begingroup\$

I think "electrical energy" is the general term for what you're describing. Look into the Telegrapher's equations for some insight on the propagation speed of waves in a transmission line. This page refers to what you're describing as "internal energy" in the drift velocity section, though I'm not familiar with this term.

\$\endgroup\$
1
\$\begingroup\$

The charge moves inside the wire, but almost all the energy flows in the electric and magnetic field outside of the wire. It is called electromagnetic energy, with the common name being light. Light is a disturbance of the Quantum Electrodynamic Field, but the math to deal with this is too complicated for electronics. As a simplification, analysis is done with the electromagnetic (EM) fields, or with photons, depending on the type of problem being solved. These are both just approximations of the underlying Quantum Electrodynamics (QED).

In general, electrical engineers don't need to know this or think about it. QED very rarely comes up in electronics. Analysis of photons usually only comes up in optical devices. Individual electrons rarely make an appearance, although the charge of an electron appears in some important formulas. Usually all that is required are the concepts of voltage and current. When things get more complicated, EM fields are required.

\$\endgroup\$
0
\$\begingroup\$

There's no single answer.

Or in other words, any single answer is going to be wrong. Different names are used in different situations.

For example, the public calls it "electric power" or "wattage." But they've got it wrong, since power is a rate, like "gallons per second." Should we call it "Joule-age?" KWH-age?

Up above 1OOKHz it's called "radio."

For example, connect a 250W incandescent bulb to an AM/CW radio transmitter output, crank up the output, and the bulb lights up normally. (A 250W bulb is roughly 50ohm resistor.) Measure the cable and you'll find 120VAC at a couple of amps. Or, instead use 50ohms of nichrome wire, and you've got an electric heater. The operating frequency is irrelevant, and your heating element glows just as well at 10MHz as at 1KHz or 60Hz.

At 10Hz-30KHz it's called "audio signals."

It's the stuff that runs along your old-style phone lines, speaker twinleads, and mic cables. A 16ohm light bulb is roughly a 1KW theatrical bulb, so hook one of those up to a large concert amplifier, and play it a pure tone at 60Hz or 1KHz. Crank to eleven. Bulb lights up normally.

What if you have an AC electromechanical oscillator connected to a resistor, and it's rotating or vibrating at 550KHz? Or 30KHz? Or 60Hz? In all cases the energy flowing along the wires into the resistor is the same stuff: "electromagnetism." Of course in each case the EM is traveling along a waveguide, a pair of wires, rather than in free space. On a waveguide we often call it "EM radiation," although of course it isn't actually "radiating" unless it escapes from the waveguide. Heat up a resistor at 60Hz, and doesn't it mean we're sending it some "60Hz radiation?"

Back before 1900, the "electrical waves" traveling along telegraph cables were a mystery. They seemed to travel at the speed of light, or a bit slower if the wires were insulated rather than bare. Oliver Lodge got into a big spitting match with WH Preece of the UK post office over the true nature of "energy propagating along wires," ...and lost the fight, even though he was right, and his math was airtight. Decades later his collected magazine columns were rescued from obscurity, to become a founding textbook for EM engineering. The Lodge Telegrapher equations were rescued from the dustbin, and despite Preece's efforts, Lodge's "loading coil" removed the chirp/dispersion from "electric waves" on 100KM conductors, making long-distance telephone possible.

Poynted

In engineering textbooks, transmission lines and the watts/cm^2 energy flows are analyzed. The motion of electrical energy is described as E cross M, poynting's vector. The joules are traveling just outside the lamp cord, not inside. So, some engineers call it 'Poynting Flow.' (Heh, but Poynting vector is itself a flow. The flowing flow of Flow, is flowing?)

What exactly do the utility companies sell? Everyone's been calling it "Electricity," but that's wrong, since the SI/NIST scientific definition of "electricity" is the coulombs, not the EM waves. The coulombs vibrate back and forth, while the KHW flies forward at roughly the speed of light.

It's low-frequency photons.

If you're a troublemaker, you could call it "photons." If photons come out of light bulbs, and photons come out of exited CO2 and ammonia gas, then photons certainly come out of magnetrons and radio antennas and power-company dynamos. There's no special frequency above which EM waves magically change into photons. It's photons all the way down. In waveguides and fiber optics and antenna lead-in wires, the energy travels as e-fields and b-fields, or as Einstein's EM quanta.

60Hz "Electricity" on the EM spectrum

I found one educator who gets it right. This was the late Frank Oppenheimer, founder of the Exploratorium museum. He publishes a famous poster of the EM Spectrum, and made sure it contains "power and telephone" down at the bottom, below the radio spectrum. Other sources never do this (perhaps believing that telephone lines involve 'electricity' rather than EM waves?) Yet even down at DC, it's still the same "em waves," and power-line radiation appears on the bottom of your VLF/ELF radio dial. Don't forget, if you connect a 1,300KM quarter-wave dipole to your electric outlet, it sends out a couple hundred watts of 60Hz electric waves right out into space. At 60Hz, so-called "electricity" would behave just like radio, if all our connecting wires weren't so darned short when compared to one wavelength.

Nikola Tesla! He had the brilliant idea to build a high-freq AC dynamo, then connect its output to a long-wire antenna and to ground, and thus broadcast very pure VLF radio, a silent CW carrier which is easily modulated with a carbon microphone. But transmitting EM energy at 20KHz, is it radio, or audio signals, or "electric power?"

:)

\$\endgroup\$
3
  • \$\begingroup\$ Thanks guys, both analogies work well, but… I'm still unclear if the same electrons are being forced back and forth past a resistor in an AC circuit? (like individual teeth on a belt drive) Do the electrons exchange or expend their negative charge in the form of heat after passing through a resistor? When an electromagnetic force pushes electrons through a resistor, how does this produce heat? \$\endgroup\$ Apr 1, 2017 at 6:10
  • \$\begingroup\$ summary of my understanding. AC generators produce Electromagnetic force which travels nearly the speed of light, switches polarities every 60Hz, (in the US) and travels along a waveguide. (the wire conductors) These EM waves physically move the electrons along the waveguide, through resistors and towards the positive side of the circuit. The EM waves also excite the electrons, which produce friction, which produces heat, which we harness for work. Loads or resistive conductors restrict the flow of electrons and somehow produce more heat. \$\endgroup\$ Apr 1, 2017 at 6:11
  • \$\begingroup\$ @EricHeagan yes, with AC the same electrons are wiggling back and forth inside resistors. Their negative charge never changes. Each electron gets accelerated by the voltage-field inside the resistor, then "collides" with resistor atoms, producing vibrations and raising the temperature. (Electrons have an average speed!) Or, imagine that a conductor's entire electron-column is "rubbing against" the frictional resistor, like oil being pumped through solid-packed sand. The sand heats up from friction! In this analogy, the oil molecules act like electrons in metal, and the sand is the metal atoms. \$\endgroup\$
    – wbeaty
    Apr 3, 2017 at 1:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.