In a simple electric circuit consisting of a load (such as a filament lamp) and a power source (a 5 V battery), when the switch is turned on the electrons experience a "displacement" which creates an electric field (which is positive in one side due to a deficit of electrons and is negative on another side due to a surplus of electrons) and the rate of flow of charge produces a magnetic field and when these electric and magnetic field come together energy is transferred from source to load.

So, does the role of electrons stop at only producing an electric field, or is there something more to it?


1 Answer 1


First rule of electronics: Lest you're doing quantum stuff, you never think about the electrons. It's not wrong to think about it, it just is of no benefit, sometimes confuses, and if you don't check your assumptions, can lead to wrong results (as you have a wrong result about power transfer!).
There's literally > 100 questions on here that ask whether we shouldn't be considering electron flow instead of current direction in circuits. And the answer has always been: no. That doesn't help.

I think you're overstating the role of the electrons, even.

The physics formulas for everything that happens outside

  1. cathode ray tubes (so, your grandma's heavy, round TV, and X-ray tubes)
  2. electrofluorescent tubes
  3. semiconductors (transistors, LEDs…)
  4. chemical elements (batteries, supercaps)

only care about the electric and magnetic field, and charge density, as well as their temporal derivative. Electrons never appear; and that's kind of physically logical, because from the descriptions of solid state physics, we know that "an electron" within e.g. a metal lattice simply ceases to be "an electron" with a place and an impulse – it gets delocated, it becomes something that changes the probability of occurrences of charges in an material, at the speed of light.

Think about it: the speed that energy travels e.g. from the moment someone switches on a light switch is not the velocity of electron drift (that would be very low, think of millimeters per second). It's the speed of electromagnetic waves (light) in a medium. So, electrons cannot be the ones actually carrying the energy from source to sink!

This gets even more important when you start considering changing fields, e.g. in a coax cable or as a free-space wave between antennas: Although there most definitely are both electric and magnetic fields between the transmit and receive antenna, not a single electron flows: Your smart phone doesn't receive a lightning strike from the base station and vice versa, they communicate through waves. That works the same in vacuum – which is why you can e.g. receive GPS signals from satellites in space. Not a single electron travels from the satellite to your phone, yet your phone detects the electric field!

So, for power transport electrons don't actually play a role – in all conductors, the power is actually transported in the fields surrounding that conductor. I found this hard to believe when I first read it, but you can do the math: within a perfect conductor, there's no electric field; so, the cartesian product of magnetic and electric field is 0 there – but that's exactly what gives us the direction and magnitude of energy transport, the Poynting vector!

Coincidentally that means that in your circuit board, power isn't mostly transported in the copper layer – even if that's where typically most losses and thus heating happens, because that copper is both thin and not a perfect conductor – but between the conductor on the top side and the ground plane on the bottom.

I mentioned the place where electrons are actually relevant above. That happens literally when we stop considering electrons just as representation of charge, but as particles that have effects each individually. In cathode ray tubes, we do that by exposing a "probability density cloud" of free-hovering electrong to such a strong electric field that they start to have enormous energy; in electrofluorescent lights, we do similar, but also let the high-energy electrons hit e.g. a mercury atom, excite that, which then, when it relaxes, releases a photon (light!).

In semiconductors, we play a lot with Schrödinger's equation; essentially, what we do is exploit the fact that an electron, as a "material" particle, couldn't come from place A to B, possibly, because there's a barrier in between. However, physics doesn't work like that, and what we consider a barrier is merely a place of zero (or very low) probability of an electron "appearing"; behind that barrier might be places where the probability might be higher, and applying external fields (not electrons) can change either the barrier or the probabilities behind, and/or we force electrons (through means of impulse) into a region with originally low probability and thus change the field.

Of course, in batteries, an electron is needed to execute a specific reaction. You ionize/deionize, reduce and oxidize metals and molecules by means of adding or detracting electrons.

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    \$\begingroup\$ As a solid-state physicist, I can say that even in SSP, considering individual electrons is only useful for illustrating effects like scattering events, but often gives wrong quantitative results due to effective mass/charge being different than for free electrons. So one just uses charge and spin current densities and respective conductance tensors. Individual electrons is useful for particle physics I reckon. \$\endgroup\$
    – tobalt
    Jul 9, 2022 at 13:01
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    \$\begingroup\$ Great answer, to clarify with an analogy for carrying the load , electrons are the people in in the bucket brigade and charge rate are the waves of buckets of water. Every "thing" is lossy with some finite heat loss, except the the electron is just the mobile force and is truly lossless \$\endgroup\$ Jul 9, 2022 at 14:26
  • \$\begingroup\$ I think much of the reason people don't recommend speaking about electrons in this context is because most people don't understand how they interact well enough to effectively teach the science (at current, myself included - pun intended). Once people learn more about electrons, and how to explain their interactions better, I expect we will experience fundamental advances in electrical engineering. \$\endgroup\$ Jul 9, 2022 at 21:58
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    \$\begingroup\$ @RockPaperLz-MaskitorCasket I would argue the opposite. Especially beginners naively think that - as current is fundamentally made of electrons - you just need to understand the electron behavior and the grand scheme will naturally emerge. But the more you understand SSP, the more you see that 'electrons' hardly exist in condensed matter. that's why we use quasiparticles like holes, cooper-pairs, excitons, magnons, plasmons etc. to describe emergent behavior. EE has made leaps when people moved away from fundamental science and adopted concepts like "inductance", "current" etc. \$\endgroup\$
    – tobalt
    Jul 10, 2022 at 6:47
  • \$\begingroup\$ @RockPaperLz-MaskitorCasket exactly what tobalt says: you simply cannot model a high frequency circuit by means of electrons. That doesn't work for free space wave propagation (as I illustrated in my answer), and it does not work for propagation on a PCB. Electrons are simply not an accurate model of reality for these kinds of problems. \$\endgroup\$ Jul 10, 2022 at 12:20

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