Talk:Moving magnet and conductor problem

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Untitled 1

Hi Steve: Although you have clarified the relation between the two frames, the notion of a "paradox" got lost in the process. The article was intended to suggest a paradox that led to the need to modify mechanics. Instead, it now is a discussion of transformations. Brews ohare (talk) 06:24, 15 April 2008 (UTC)[reply]

Hmm. In point of fact, there isn't any paradox; I figured that the top would explain why one might think there was a paradox, and the rest of the article should systematically explain it and make it clear that there's nothing paradoxical. But I guess I've never really understood what this article is trying to do and say. You're welcome to change it back if you want. --Steve (talk) 17:59, 15 April 2008 (UTC)[reply]

I think the interesting point that I was trying to make when I started this article was that

the laws of electrodynamics and the mechanics at the time of the development of special relativity were inconsistent with each other, so one or the other of the other of the two theories would have to be modified, and
surprisingly, it turned out that it was mechanics that had to be modified rather than the new theory of electrodynamics. Complexica (talk) 20:49, 23 May 2008 (UTC)[reply]

Ah, that's different from the reason that I learned for what the "moving magnet and conductor problem" is, which I guess came from Griffiths' textbook, and also Einstein's relativity paper. There, everything's done to lowest order in v/c, and you use Galilean transformations, and everything's consistent, but the "problem" is that what's an electric force in one frame is a magnetic force in another, and it's an unexplained coincidence that these forces should happen to be exactly the same in magnitude.

In the pedagogical presentation I'm familiar with, the "problem" you're referring to is, the "constancy of the speed of light" problem. Of course, any situation where you change the frame of reference will have inconsistencies if you use Maxwell's equations and Galilean transformations. But the constancy of the speed of light is where it's most obvious and simple, moreso than in the moving magnet and conductor problem. --Steve (talk) 17:40, 24 May 2008 (UTC)[reply]

Untitled 2

This article is very interesting but the role played by special relativity (SR) in resolving the "moving magnet and conductor problem" is unclear.

1- "In addition to consistency, it would be nice to consolidate the descriptions so they appear to be frame-independent. A clue to a framework-independent description is the observation that magnetic fields in one reference frame become electric fields in another frame".

For small values of v, the Lorentz transformation will convert the pair (E,0) into (E',B') with E'#E and B'#0. May be you should explain how the requirement for converting (E,0) into (0,B') can be fulfilled for any value of v. Only then will the equivalence of both theories be demonstrated.

2- "The same phenomenon would seem to have two different descriptions depending on the frame of reference of the observer".

Descriptions according to either the magnetic or the electric theories are produced by theoreticians, people who are not involved in the experiment. The Lorentz transformation caters for equivalent descriptions of the same electromagnetic field, which is not directly observable. The problem to be resolved refers to one single experiment producing a single output (the intensity of a current) which both theories are able to predict correctly. Swapping between both theories requires a change of reference frame. Per definition, this does not affect the relative motion between any pair of physical objects: only the list of objects being at rest has changed.

Conversely SR deals with two observers running similar experiments in different experimental conditions, thereby obtaining different results for their respective measurements. The Lorentz transformation traces the divergence of observable outcomes between two experiments. Both observers measure the length or the period of the same object, one being at rest and the other one being in motion in respect to this object. Swapping between experimental conditions cannot be dealt with formally through a change of reference frame, since the relative speed between the observer and the target object changes from zero to v.

So the set of conditions which prevails for deriving the Lorentz transformation in the SR context does not match at all the description of the problem at stake. May be you should clarify what is the rationale for invoking SR in the discussion of the "moving magnet and conductor problem".Sugdub (talk) 16:49, 28 November 2012 (UTC)[reply]

The situation is 100% identical from any frame. If you go into the magnet frame, the magnet sees electrons moving through it's fields of varying strength i.e. a changing magnetic field ---> Curl E. Magnetic fields NEVER directly influence charged particles!

The entire thing is ludicrous! :) Hosh1313 (talk) 07:51, 21 May 2023 (UTC)[reply]

Untitled 3

I was looking for, but did NOT find it: A real experiment involving an electromagnet that is switched on and off, a short piece of copper wire or a coil situated within the magnetic field, and a sensitive voltmeter connected to the two ends of that wire. As that electromagnet is switched on a voltage pulse would be generated as shown on the voltmeter in one direction, and as the electromagnet is switched off that would result in a voltage pulse in the opposite direction. What quantitive relations can be measured?

And how about a different experiment during which the magnetic field is measurable and variable and so is its rate of change in both directions.70.27.152.243 (talk) 23:35, 8 July 2016 (UTC)[reply]

Untitled 4

I can't follow the proof, in the section "Transformation of fields, assuming Galilean transformations", subsection "Conductor frame". Suppose the relative motion between the magnetic field and conductor is along the X-axis, and suppose the magnetic field is constant through space and everywhere directed parallel to the Z-axis. Then in the conductor's frame of reference, there is no changing magnetic field anywhere. In this case you'd need Special Relativity to prove the result, so this "Galilean proof" seems dubious to me.— Preceding unsigned comment added by 2600:8800:7b84:7000:918f:eaf2:ae46:8d5e (talk) 07:46, 29 October 2017 (UTC)[reply]

Suggest "Newton's law of motion in modern notation" section to be deleted.

The section doesn't seem to add anything to the article. Its only readable by specialists. It might be appropriate for a physics textbook for upper division dynamics, but it not useful for the average reader (or even the better than average reader) of physics articles. Constant314 (talk) 19:36, 12 March 2019 (UTC)[reply]