Talk:Magnetic flux

Article Does Not define magnetic Flux

This article should be deleted because it is useless as a definition. There is no place where it shows how to calculate the magnetic flux from a definition of it. Of course engineers have been designing electric machines for over 100 years using this concept, so there is a way to do it. Since magnetic flux is the dual concept to quanity measure of electricity or charge, it is important that a procedure be given to calculate magnetic flux. But I can't find it here.

According to history, the above was written by 71.251.190.82. I made the heading. --Treekids (talk) 18:40, 12 June 2008 (UTC)

I agree- the definition is inaccurate and tautologous when corrected. Magnetic field (H) is a completely different concept from flux, and if you replace the erroneous 'field', by the correct 'flux', the defintion becomes 'Flux is the amount of flux'. What kind of defintion is that ? What kind of imbecile has written this crap anyway ? —Preceding unsigned comment added by 82.32.49.157 (talk) 19:31, 28 February 2011 (UTC)

The intended definition was the tautologous one (B) not the incorrect one (H). I reworded to make that clearer.

For a non-tautological definition...I don't know. It's a hard thing to "define", being a physical thing in the real world. If you have a good way to do it please go ahead. One strategy is to look at how it's defined in textbooks. --Steve (talk) 20:06, 28 February 2011 (UTC)

Physically speaking, "flux" is the amount of flow through a surface. In the case of magnetic flux, we're talking about the number of imaginary lines flowing through an imaginary surface. Those imaginary lines are magnetic force vectors. i.e. the vectors that represent the force that a magnetic object will experienced if placed into the magnetic field. There is no universally accepted physical explanation of what that field is. It's action at a distance. Just not instantaneous. 2603:6080:CC00:193:C9E2:11BE:C088:7008 (talk) 20:25, 4 August 2023 (UTC)

Proof

The given "proof" that the flux through a closed surface being zero seems backward. It starts from a vector potential A with curl A = B and then proves that div B = 0. In reality it is just the opposite. One of Maxwells laws states that div B = 0. As a consequence there is a vector potential A with curl A = B. −Woodstone 21:42, 2005 Apr 9 (UTC)

adds and removed

I added the reference to Maxwell's equations because of that, but it is still unsatisfying. Lemme see how it can be reworded. --Laura Scudder 23:32, 9 Apr 2005 (UTC)

I just removed the reference to the vector potential since it has no direct connection to discussion. --Laura Scudder 23:43, 9 Apr 2005 (UTC)

Equations need revamping

This page needs to have variables explained better. I added some explanation, but others I'm not sure how to expand on. Also, am I right that B (the magnetic flux density) is the same thing as a "magnetic field" ? If so that should be noted, because both terms are common.

No - flux density (B) and field (H) are completely different concepts with different dimensions and units (Tesla and A/m repectively in the SI system). B = Hu where u (mu) is the permeability of a material. u has units of Henry/metre; u0, the permeability of free space is 1.257*10^-6H/m. The problem is that in the USA writers are extremely careless about use of the term 'magnetic field', and habitually confuse it with flux density. God knows how they can do science or engineering with that kind of mind set. Possibly the reason for this is that in that country the cgs system is still in use, and in that system B and H are identical (so I have been told, but I have never used that system of units myself). —Preceding unsigned comment added by 82.32.49.157 (talk) 19:39, 28 February 2011 (UTC)

Some people use the terminology that B is the "magnetic field" and H is the "magnetic H field". That doesn't make them stupid or careless or incapable of doing science or engineering. It's just a different terminology. For example, Americans are still capable of playing "football" even though they think the word "soccer" means "football" and the word "football" means something different. At the World Cup I didn't see the American team throwing the ball to each other or wearing helmets.

That said, of course on wikipedia we should define things in a way everyone will understand. I edited the lead accordingly. I hope I didn't miss anything. :-) --Steve (talk) 20:00, 28 February 2011 (UTC)

"Layman"

The article states that:

Magnetic flux density, otherwise known as magnetic field density, is essentially what the layman knows as a magnetic field

It's also what pretty much every physicist knows as the magnetic field, and authors like Jackson and Griffith concur on such usage. So I think "the layman" here is a bit misleading. --Starwed 13:08, 27 February 2007 (UTC)

No - the layman and the scientist or engineer differ here - see my comment immediately above. AJS —Preceding unsigned comment added by 82.32.49.157 (talk) 19:41, 28 February 2011 (UTC)

Didn't get the definition

I want an easier definition because I didn't get that one. ClintJCL (talk) 02:18, 4 December 2012 (UTC)

"Definitions" are tricky in physics articles because you are talking about a real-world thing. You describe it rather than define it - by pointing to examples of it, listing its properties, etc. (How would you "define" Mount Everest? Maybe you would say where it is, how tall it is, show a picture of it ... but that's not really "defining" it, just "describing" it.) When you describe a real-world thing (like "magnetic field" or "Mount Everest") in sufficient detail, there is no ambiguity about exactly what it is -- it is therefore 100% precise. But you cannot necessarily sum it up in one crisp sentence to open an article. This is a challenge particularly for the magnetism articles, although I have occasionally seen complaints about "circular definitions" or "imprecise definitions" in many different physics articles.

I am not saying that there is no room for improvement in the opening definition. Just want to say why I think it's very hard to make it sound perfectly clear and accessible. --Steve (talk) 04:28, 4 December 2012 (UTC)

Template:Electromagnetism vs Template:Electromagnetism2

I have thought for a while that the electromagnetism template is too long. I feel it gives a better overview of the subject if all of the main topics can be seen together. I created a new template and gave an explanation on the old (i.e. current) template talk page, however I don't think many people are watching that page.

I have modified this article to demonstrate the new template and I would appreciate people's thoughts on it: constructive criticism, arguments for or against the change, suggestions for different layouts, etc.

To see an example of a similar template style, check out Template:Thermodynamic_equations. This example expands the sublist associated with the main topic article currently being viewed, then has a separate template for each main topic once you are viewing articles within that topic. My personal preference (at least for electromagnetism) would be to remain with just one template and expand the main topic sublist for all articles associated with that topic.--DJIndica 16:45, 6 November 2007 (UTC)

+ or -

${\mathcal {E}}=\oint \mathbf {E} \cdot d\mathbf {s} =-{d\Phi _{m} \over dt}.$
Better: + or -
Martin Segers (talk) 08:24, 6 January 2008 (UTC)

gibberish

Figure 3: A vector field F ( r, t ) defined throughout space, and a surface Σ bounded by curve ∂Σ moving with velocity v over which the field is integrated.

Can someone re-word this? --Treekids (talk) 18:38, 12 June 2008 (UTC)

Flux through an Electric coil?

What is the definition of flux through a coil doing there? Its nothing more than applying the general definiton of magnetic flux (in fact the equation is a repeat of the definition - and once again the dot for the dot product is missing). The section is too short anyway, hence its redundant. The section makes it appear that the flux through a coil has a seperate/special case definition.

On the other hand - the video is certainly good to include.

Given these issues - I deleted everything in the section except the video and a sentence related to the video.

If there is any favour to restore the section and extend it to some volume - please do. F = q(E+v×B) ⇄ ∑_ic_i 13:59, 25 March 2012 (UTC)

Many images...

I also tried to tidy the positioning of the images - if according to your browser the images still are cluttered: tweak as neccersary. F = q(E+v×B) ⇄ ∑_ic_i 14:01, 25 March 2012 (UTC)

==

Sign of Field Lines

The text states "(see below for deciding in which direction the field lines carry a positive sign and in which they carry a negative sign).", but there is no further mention of this.

Modelmat (talk) 08:57, 24 March 2021 (UTC)

Equation for Magnetic Flux is Mathematically Incorrect

The equation for magnetic flux on the page says that Φ = B⋅S = BS sin θ. I don't know what the literature says on the subject, but this equation is mathematically wrong. The dot product of the two vectors B⋅S is BS cos θ. For it to be BS sin θ, you'd need to be talking about the magnitude of the vector B×S or the magnitude of the bivector B∧S. 2603:6080:CC00:193:C9E2:11BE:C088:7008 (talk) 20:03, 4 August 2023 (UTC)