A base-level question about electromagetism, magnetic fields, & conductors - Page 1
Forum section: electronics / general

author: cvanc
author_rank: Frequent Contributor
timestamp: September 29, 2023, 05:23:42 pm
content: "Magnetic fields arise from the motion of electrons in a conductor" is a rule known to us all.But if you could magically convince the same number of electrons to travel the same pathwithouta conductor you would get the same magnetic field, correct?In other words the physical structure (conductor) can be thought of as an electron holder and it's the electrons alone doing the work.

author: ataradov
author_rank: Super Contributor
timestamp: September 29, 2023, 05:37:23 pm
content: Any structure that allows electrons to flow is a conductor. So, if you convince electrons to flow in some material, that material is a conductor, at least under the "convincing" conditions

author: TimFox
author_rank: Super Contributor
timestamp: September 29, 2023, 07:30:17 pm
content: The beam of electrons runningin vacuumdown the column of a particle accelerator (synchrotron, Van der Graaf, linac, etc.) induces an external magnetic field proportional to the current flow thereof.There are several vendors who sell magnetic-field sensors (either simple toroidal-core coil or a DCCT) to measure the beam current as a diagnostic for the accelerator user.A very long article from CERN about beam diagnostics in accelerators:https://cds.cern.ch/record/499098/files/p154.pdfSee section 2.01

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 29, 2023, 09:22:55 pm
content: Quote from: cvanc on September 29, 2023, 05:23:42 pmYes. That's called a CRT. Not magic.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 29, 2023, 09:51:11 pm
content: Quote from: ataradov on September 29, 2023, 05:37:23 pmThat kind of reminds me of an older topic and a number of associated videos...

author: IanB
author_rank: Super Contributor
timestamp: September 29, 2023, 09:53:09 pm
content: Quote from: cvanc on September 29, 2023, 05:23:42 pmIt's not "motion of electrons in a conductor", it is "motion of charge relative to an observer". The presence of "an observer" surreptitiously invokes special relativity. You may find this video interesting:

author: soldar
author_rank: Super Contributor
timestamp: October 01, 2023, 09:44:49 am
content: Quote from: IanB on September 29, 2023, 09:53:09 pmIf a charge is in motion in the woods where there is no one to observe it, does it create a magnetic field? Or does it dispense with that because it would be a wasted field?

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 01, 2023, 03:28:46 pm
content: Quote from: soldar on October 01, 2023, 09:44:49 amSince you said 'in the woods', it would create a magnetic field, with respect to the trees. Haa-haa!The joke question has a kernel of truth, though: whether an electromagnetic field even exists if it does not interact with anything. That can probably drive theoretical physicists mad, while non-theoretical physicists just observe that it does not matter. (I think I lost a pun in there somewhere, sorry.)

author: woofy
author_rank: Frequent Contributor
timestamp: October 01, 2023, 05:48:56 pm
content: Quote from: Nominal Animal on October 01, 2023, 03:28:46 pmReminds me of:To the pessimist, the glass is half empty.To the optimist, the glass is half full.To the engineer, the glass is twice as big as it needs to be.

author: switchabl
author_rank: Frequent Contributor
timestamp: October 01, 2023, 07:00:38 pm
content: In classical field theory, it is really just a question of the coordinate system. A co-moving observer is strictly optional and unlike in quantum mechanics, "measurements" or "observations" play no special role. The question whether the fields are "actually real" is more one for the philosophers than for the theorists.Or in other words: well, technically, that's not a glass, that's a mug. Also, that doesn't look like half to me, how did you even measure that? (I am a lot of fun at parties.)

author: IanB
author_rank: Super Contributor
timestamp: October 01, 2023, 08:01:16 pm
content: Quote from: switchabl on October 01, 2023, 07:00:38 pmBut according to the video I linked above, in classical field theory the equations for electromagnetism do not explain all observed phenomena and contain inherent contradictions. A change of reference frame can lead to problems.Only when Einsteinian relativity and length contraction is included in the analysis it is possible to make sense of all observations.

author: switchabl
author_rank: Frequent Contributor
timestamp: October 01, 2023, 08:23:55 pm
content: What we call "classical" electrodynamics today already has special relativity baked in. It is understood that everything happens in a Minkowski space-time and that coordinate systems are related by Lorentz transforms (which convert between electric and magnetic fields and include effects such as length contraction and time dilation).In modern physics, the word "classical" almost always just means "non-quantum". So I wasn't referring to pre-1900 electromagnetic theory; but I can see where that might be confusing.

author: RJSV
author_rank: Super Contributor
timestamp: October 04, 2023, 11:51:32 pm
content: In my training, a pure beam of electrons will repel each other, (being 'like' charges), which are focused in the CRT case, to counter the tendency to spread out during travel.Actually surprised, that similar situation, going down a wire, isn't the same, as far as the generated magnetic field, thinking the atoms etc. in a copper wire will have positive charges that balance the negative (moving) charges. Or did I read previous posts wrong ?(thanks)

author: RJSV
author_rank: Super Contributor
timestamp: October 05, 2023, 12:00:06 am
content: ...I've usually put up my own red flag, when a non-classical theory framework is discussed, (subjects like 'Quantum' physics are notorious, in other threads.)Listened, recently, to some 'medical' descriptions, blatent abuse of terms like 'frequency'...as in "Bad frequencies must be purged...by flooding the Patient's body, with cancellation waves...".Those frequency cancelling effects seem to forget, about wave phase relations, in other material I've seen.Just reminded me, as seen elsewhere.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 05, 2023, 12:34:07 am
content: Although full of equations that must mean that it's all very serious stuff, admittedly a number of modern physics theories suspiciously look like dodgy alternative medical therapies.That reminds me also of this user who was talking about aether and hugging photons and stuff. While the whole thing looked quite funky, it wasn't that much funkier than string theory. Oh well. Oh so little we know.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 05, 2023, 02:36:09 am
content: Quote from: RJSV on October 04, 2023, 11:51:32 pmYes. The copper nucleii provide a positive charge to balance out the electrons and make the whole thing net neutral. This creates a screening potential that reduces the effective range of the coulomb interaction dramatically and allows electrons to approximately move as free particles.That's basically why we have wires. Electron beams in vacuum theoretically have "zero resistance" but you are limited to very low density of charges before the mutual repulsion causes a problem.Conductors are a bunch of positive charges that allow you to cram many orders of magnitude more electrons in a given space and conduct a lot more current. The problem is that the positive charges tend to get in the way of the electrons. What makes a good conductor is that the nuclei arrange themselves such that they screen the charges while still allowing free movement of the electrons.