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I am still learning my ropes around the wiki and I appreciate your effort here. Science involves consensus and while a consensus of two isn't very good it beats a consensus of one by quite a bit. Personally, I think that a wiki like this should follow the model used for coding large software projects of having all articles peer reviewed before before committing. As long as you or someone else (and better yet a bunch of people) are willing to help, I will follow that model.
(By the way would it be better to edit your original response or to copy it as in here?)
Anyway, I'm just one guy, and you're welcome to disagree with and ignore any of those suggestions. Also, I don't know if anyone else will offer feedback, you may want to sit on it a few more days before posting, at your discretion. Also, I tend to prefer big all-at-once changes to a zillion small ones, but maybe that's just my opinion.
TStein ( talk) 19:19, 19 May 2008 (UTC)
Here's the link to the page.
Ok, I am almost to the point where I am ready to commit my changes. I dealt with most of the issues that Steve raised. I left a minor issue or two for others to fix. I made some larger changes to the visualizing the magnetic field section. I also got a good start on the H field section. I am not as comfortable with the H field as I would like to be, so help would be appreciated there.
Other problems: I included 2 images as placeholder until better images can be found.
I did not like any of the right hand rule images because most of them had little to do with F = v×B. They mostly had to do with generating current when pulling on a wire. The signs are reversed for these 2 cases.
The second image was an attempt to sketch Earth's magnetic field including a 'magnet' in the interior. I thought it might help people to see approximately where Earth's magnetic field is generated and what is the polarity of that magnet. I found a lot of similar stuff on the web but all of them had the wrong pole of a magnet (N) under Earth's N magnetic field. Unfortunately my attempt had the field lines to rounded, which I could fix if I had the time. Worse, the arrow heads that show up on my svg viewer fx 2.0 are not showing up on wikipedia's viewer.
TStein (
talk)
05:57, 23 May 2008 (UTC)
Incarnation seems to me a poor word choice. It means in the flesh, kind of like when a god becomes human. I'll think of a better word. Daniel.Cardenas ( talk) 14:53, 23 May 2008 (UTC)
I saw this fifty-minute NOVA documentary that addressed the problems our magnetic field has -- it's getting less and less powerful by the day. Some say it's just a normal 10,000-year cycle from which the source of magnetism will change direction. Basically, said in everyday language - "south" becomes "north" and vice versa. As the transicion will occur, it is expected a 10% increase of people with skin cancer. Now, does anybody think we should add this piece of information?
-- 96.232.60.47 ( talk) 21:09, 28 May 2008 (UTC)
There is still a lot of work that has to be done in cleaning this article up. There were some problems introduced, such as with the 3 figures I added. (Magnetic field with compasses, right hand rule and Earth's magnetic field.) Overall, though I think it is a large enough improvement over the previous case to justify the edit.
The main reason I am doing this, though, is to avoid the difficulties in keeping my branch in synch with the article. Plus I am hoping to get more eyes on this page.
Still needs:
I am willing to push this article forward as far as I am able. Right now I need more eyes on the problem, though. Personally, I think this can and should be pushed to being a FA.
TStein ( talk) 16:56, 2 June 2008 (UTC)
Pol098 has just put in a paragraph differentiating between the "magnetic field" and the "electromagnetic field", in particular saying that the latter is only associated with electromagnetic radiation. I don't think that's right. I think the "electromagnetic field" is just the electric field and the magnetic field put together into two words. A magnet does have an electromagnetic field: its electromagnetic field consists of zero electric field and whatever magnetic field.
I don't have a textbook on hand to confirm this, but one piece of evidence is that the so-called " electromagnetic field tensor" (which, one would think, should describe the electromagnetic field) includes any magnetic and electric fields, not just those that make up EM waves. In particular, the electromagnetic field tensor (and hence, I think, the electromagnetic field itself) is certainly not zero around a stationary magnet.
Or maybe I'm way off. What do other people think? Can anyone find reliable sources on this? -- Steve ( talk) 20:28, 29 August 2008 (UTC)
I am trying to do a back-of-the-envelope calculation and navigated to this page for a definition of B and H fields. The page fails to cover these very fundamental in anything approaching clarity. The B field defintion is turgid and buried halfway down the page. The H field definition is more alluded to than buried. ~Paul V. Keller 16:25, 1 January 2009 (UTC)
I have objections with the following statement as being misleading:
It is true that starting from a pure Electrostatic term one can arrive at the above statement. It is also true that all of Maxwell's equations can be derived from Coulomb's Law (with some difficulty). (One has to be careful, amongst many other things, not to also 'prove' that gravity follow Maxwell's equations as well.) The first problem I have is that, as far as I can tell, there is no reason to assume there is one reference system that is purely electrostatic for real systems of charges. A more important pedagogical reason is that there is no reason to favor the Electric field in this way. In relativity, boosting a pure electric field will result in an electric plus a magnetic field, true. It is also true, though, that boosting a pure magnetic field will result in a magnetic field plus an electric field!. There is no a priori reason to think that the electric field is any more fundamental then the magnetic field. Advanced theories all treat E and B on equal footing. (Together they form an anti-symetric 4-tensor).
All of this is covered above from the last time that this type of statement was placed in this article. The end result was that the sentence was altered to be more technically true from the above perspective. This process already been done at least twice and vestiges from this slow motion edit war can be found sprinkled through the article.
This article is already polluted enough. As an example of this see the section directly above this one on this discussion page. (Unfortunately, I myself have contributed a good portion of that pollution as I have strugled to learn how to write encyclopedia articles well.) I was hoping that we can reach a consensus so that we can stop the madness. TStein ( talk) 15:44, 23 January 2009 (UTC)
There seems to be too much in this article about the difference between B and H. The two are related by the simple equation B =μH where μ is the magnetic permeability. B is the magnetic flux density which depends on the permeability of the medium. In Maxwell's books the permeability would be a measure of the density of magnetic field lines for a given magnetic field strength H.
B is essentially a weighted version of H which seems to make it a more useful quantity. Maxwell tended to use the product μH. I can't think that there's much more that needs to be said about the inter-relationship between these two quantities. I might want to take everything out regarding B and H, and put this short paragraph in instead. David Tombe ( talk) 20:56, 28 March 2009 (UTC)
Steve, In a bar magnet and all ferromagnetic materials, μ is huge. Therefore B will be huge even if H is small. I cannot believe that the magnetic field strength H is precisely zero inside a bar magnet. That wouldn't make any sense. There has to be a magnetic field inside a bar magnet. Who told you that there is no magnetic field H inside a bar magnet? David Tombe ( talk) 17:16, 29 March 2009 (UTC)
Steve, There is still a magnetic H field present when hysteresis takes place in a bar magnet. Hysteresis is a topic similar in principle to when Hooke's law breaks down due to elastic deformation. You are quite entitled to write a section on hysteresis. My point was simply that B =μH is the general rule, as like Hooke's law, and that there is an awful lot of unnecessary discussion in the main article about the distinction between B and H. I explained that distinction. Why do you need to bring hysteresis into it? It's like having endless discussion about the difference in meaning between 'Force' and 'extension' in Hooke's law. Someone points out Hooke's law as F = -kx and then you come along and introduce cases where Hooke's law breaks down due to the elastic limit having been reached. David Tombe ( talk) 23:15, 29 March 2009 (UTC)
Steve, I wasn't saying that force is the same as extension. I was making the analogy between 'Force' and H on the one hand, and between 'extension' and B on the other hand. It is by no means a perfect analogy. I was merely using a cause/effect analogy to make the point that in an encyclopaedia, one begins with the most basic general rule.
Hysteresis is a specialized topic, not fully understood, and which involves a certain amount of shielding and delayed reaction as between cause and effect.
In principle, B =μH as a general rule. There are far to many instances on the main article of people trying to learn this general rule on the job. It could be grossly simplified. Then if you want to write about Hysteresis, feel free to do so. David Tombe ( talk) 21:28, 30 March 2009 (UTC)
In order to make at least a first stab to address the problems of the relationship between B and H, I made a number of small changes that I hope are in the right direction. (Although, I think the net effect is to increase the size of the article :( ). First of all I added the linear relation B = mu H to a number of different locations that should have already have it. I tried to emphasize the importance of that equation even while stating directly what the problems were. Second I tried to clarify the difference between B and H and hopefully made it a little more evident why this is important.
The second step is far from complete. I also realize that there is a difference in how physicists (like myself) approach this then how engineers approach it. The B vs H section is written from the physicists perspective. I have tried to respect the engineer's approach by making this section as short and as clear as I can (at this point) while keeping the fundamentals that are necessary from the physicist's point of view. There is still work to be done there, though I think that it is much better from my point of view. TStein ( talk) 16:17, 31 March 2009 (UTC)
Tstein, you're learning. The next stage is to see if you can explain displacement current in a way that fits with the EM wave equation, without using the aether.
Meanwhile, I think we are stuck here with no choice but to list B = μH as an accepted fact of which the explanation which existed in the 19th century is now denied. There is no existing explanation, and that is what has caused all the confusion on the main article. Relativity cannot explain μ. The equation which Stannered mentioned above is merely an extension of the basic equation. David Tombe ( talk) 13:16, 1 April 2009 (UTC)
Tstein, I have no quarrel with the existing equations. But from what I can see, the original meaning of the relationship B = μH was lost when Maxwell's vortex sea was abandoned. Nevertheless, I agree that B is by far the more useful quantity, and indeed in most of Maxwell's writings, he uses the product μH. From what I can see, M is to atomic and molecular matter, what H is to the abandoned vortex sea. And becuase the vortex sea has been abandoned, nobody knows how to explain the meaning of H. All they know is that it fits into the maths.
For Maxwell the quantity corresponding to H was more accurately the circumferential speed of one of his molecular vortices. This circumferential speed is what contributed to the pressure between adjacent magnetic lines of force, and hence caused magnetic repulsion. The vortices were aligned solenoidally along their rotation axis, and as you know, the magnetic field lines between like poles spread outwards in the space between the poles, and come together laterally. Maxwell ascribed the magnetic repulsive force to centrifugal force in the equatorial plane of the vortices. The circumferential speed of the vortices was a measure of their vorticity, and so H can be seen as a measure of the vorticity of a single magnetic line of force. With the μ term added, we then obtained a kind of magnetic flux density B, because μ was considered to be related to the density of the vortex sea. Hence B is magnetic flux density and it is equal to μH, where H is a measure of vorticity or magnetic field strength. The modern definition of H is purely mathematical, and so it will be very hard to ascribe a physical significance to it in the absence of Maxwell's vortex sea. David Tombe ( talk) 19:08, 13 April 2009 (UTC)
Since this article has finally gotten some of the attention it deserves with more then one active editor I thought it prudent to discuss possible large scale changes to avoid butting heads.
Issue 1: large scale reorganization. A while back I reorganized this article to enumerate the field sources together and then the elementary effects together. This brings me to Brews Ohare's edit to magnetic dipoles. At first I was mildly annoyed that Brews Ohare included information about how magnetic field affected the dipole with a torque in the dipole as sources of B field section. Then I realized that splitting up the dipole interaction into 2 sections one for creation of the field and the other for interaction may have hurt the article. I liked what Brews Ohare did there. Maybe it is more important to organize both dipole sections together (creation of B and interaction with B) and do the same for both magnetic field and currents sections, etc.
Issue 2: In my opinion we need to keep permanent magnet section near the very top and separate from magnetic dipoles. My main reason for this is that all articles have to start with the simple and familiar before going to the more complicated and unfamiliar.
Issue 3: In my opinion we need to keep the magnetic field lines and visualizing them section near the very top just after the discussion of the permanent magnets (including compasses). In particular the section on magnetic fields alwas comes in loops sets up a lot of the understanding that is needed for later. Plus people should be fairly familiar with seeing field lines.
Issue 4: Consistency with the level of complication. What level of detail are we looking for here? Right now we have the Landau-Lifshitz-Gilber equation but not the Biot-Sarvart Law nor Maxwell's equation. If we included every equation at the level of L-L-G would we have enough room for the article to be qualitative? In my opinion an article like magnetic field needs to be simple with links to the more in depth stuff. Alternatively every section could start off simple then work toward the complex. Having the article with a repeating patern of easy to complex, easy to complex sounds like a way to lose everyone, though. Then again I don't claim to be an expert in that matter.
Issue 5: When to use magnetic field and when to use magnetic B-field is a question that Brews Ohare brought to my attention by his edits. After some thought I am convinced that we should use magnetic field (implying both B and H) for any source of magnetic fields, BUT I think we should use the magnetic-B field for any affect. The magnetic-H field is largely a theoretical construct that has no effect on anything. It cannot be directly measured typically. It is the magnetic B-field that pushes stuff around.
I hope this gives a good indication of my thoughts at least so that we can come up with a good solution and really make this article shine. TStein ( talk) 21:25, 3 April 2009 (UTC)
It seems the article often used the constructions "magnetic B-field" and "magnetic H-field"; I have tried to eliminate the word "magnetic" in these combinations, as it seems to contribute nothing. Brews ohare ( talk) 17:18, 7 April 2009 (UTC)
Are we then going to leave it that Poisson's great approach relating to B and H, which worked so well, only worked by coincidence even though it was wrong? That's what it says in the main article. What about wording it more neutrally, something along the lines of, 'despite the success of Poisson's approach, it is no longer accepted in modern physics, and no alternative approach has yet taken it's place?'.
As regards Maxwell, there are a few inaccuracies in the article. You will have a hard job finding any references to electric charge in Maxwell's 1861 paper. The closest that he comes to it is with 'density of free electricity'. Maxwell tends to work in terms of force per unit volume, with the volume term incorporated into a kind of density term. The density term corresponds reasonably closely with the modern day charge to mass ratio, and so his electromotive force terms tend to correspond to 'electric field'. David Tombe ( talk) 12:29, 17 April 2009 (UTC)
I'll try. But from what I can see, the modern explanation is nothing more than a mathematical definition. I could probably fix up the bits about what Maxwell said and then leave it for somebody else to do the rest. David Tombe ( talk) 14:12, 18 April 2009 (UTC)
Presently, the history section reads too objectively, I think. Rather than, "this approach was wrong," we should suggest that modern science offers a more complete alternative theory. The current theory appears to be valid, but we certainly don't know that it's "correct." -- Jeff Wheeler ( talk) 03:56, 23 October 2009 (UTC)
This topic is a delicate one, as reading the talk pages at Faraday's law of induction will illustrate. The main problem is that Faraday's law in terms of flux density covers both motional and transformer EMFs, and of course both have enormous practical use in motors and generators. However, the Maxwell relation using curl E that is one of Maxwell's equations does not include motional EMF, and so is not equivalent to the first law, although often referred to as Faraday's law nonetheless.
Including the motional EMF makes for a a complicated equation. One has several options here: (i) put in the gory details (ii) leave out all the equations and stick to words (iii) keep the flux density equation and dump the partial DE using curl (iv) try to cover the matter at several levels by putting in enough verbiage to cover things for the casual reader, but retaining the mathematical expression.
Further revisions of the section Magnetic_field#Electric_force_due_to_a_changing_B-field may be advisable, but it requires some care Brews ohare ( talk) 06:25, 3 May 2009 (UTC)
There is no "controversy" here. The distinction between motional and transformer EMF is real and well-documented. It prompted some of EInstein's thought about relativity and formed the preamble to one of his famous papers. It has been remarked upon by Feynman (see the Faraday's law of induction article). It has very noticeable practical consequences.
Two usages of "Faraday's law" are in the literature. This kind of multiple usage occurs all through physics, and often seems to lead to sides being taken about who is "right". The real point is that Faraday's law of induction is a significant topic and covers two phenomena while the Maxwell-Faraday equation covers one of the two. So what do you want to do? I'd say cover both.
I think your statement : "The way I see it, we can either deal with every petty 'controversy' about naming conventions or we can write a great article." is wide of the mark. Brews ohare ( talk) 21:43, 4 May 2009 (UTC)
I have attempted to simplify this discussion using some of your suggestions. Brews ohare ( talk) 22:52, 4 May 2009 (UTC)
This article seems rather long. Suggest shortening. For example history of B and H to be moved mostly to sub article. Other sections towards the bottom of the article that already have subarticles should be shortened to a paragraph. What do you think? Daniel.Cardenas ( talk) 04:57, 28 May 2009 (UTC)
I think I saw on wikipedia a comparison of different magnetic field strengths. Does someone know where that is at? Should we put it in this article? Thx, Daniel.Cardenas ( talk) 04:57, 28 May 2009 (UTC)
(UTC)
Why isn't there a differential form of the magnetic field such as:
For a line current? I think those let you see very easily the connection to the rotational form in Maxwell's equations. —Preceding unsigned comment added by 169.198.254.6 ( talk) 14:38, 12 June 2009 (UTC)
I removed the following because I could find nothing to support it:
The magnitude of B is defined (in SI units) in terms of the voltage induced per unit area on a current carrying loop in a uniform magnetic field normal to the loop when the magnetic field is reduced to zero in a unit amount of time.
The best I could find is that (conceptually) the Weber is defined by the flux law, while Tesla is defined conceptually as a Weber/square meter. In practice, the unit of Tesla is typically determined using properties that are way beyond the scope of the article. The B fields has many potential definitions based on its effects and it seem superfluous to chose one that is not even used in practice to set the standard for how to measure the unit.
Are there any 'official' definitions of B or H out there? TStein ( talk) 21:36, 12 June 2009 (UTC)
The first thing the reader is told is that a magnetic field is a vector field. Not only is this meaningless to most readers but a) appears to avoid the task of defining the topic and b) sounds a lot like mistaking the map for the territory. Some of you may be so immersed in the theory that you have difficulty explaining the phenomena in plain language. This is not anywhere near my area of expertise but how about something like this: "Magnetic fields are a cloud of forces that surround magnetic materials and electric currents. These forces can be detected by their interaction with the magnetic fields of other magnetic materials and electric currents."? Jojalozzo ( talk) 19:52, 8 July 2009 (UTC)
The enterprising lay reader who can get past the first sentence, will find "dipole" introduced in the second without any explanation, not even a responsibility-avoiding link. The only people who are likely to understand this introduction already understand enough to skip it. This article would be much improved if the intro gave non-experts a good idea of what is known without them having to refer to other articles or reference materials. Jojalozzo ( talk) 20:08, 8 July 2009 (UTC)
I would love to make the first sentences more accessible and those terms used too early bothers me as well, but I have not seen a better alternative. One thing we have to keep in mind is that the lede section is not an introduction. The lede section has to do several (seemingly mutually exclusive) things:
We should always strive for the third, but we have to be careful not to sacrifice too much of the first and the last. Using technical terms in the lede does not bother me too much provided that they are explained in the article and that they are directly related to the subject of the article. The term vector field fits both of these dipole probably does not.
All of the above examples, so far, have failed to be reasonably technically correct; in particular, they grossly misuse the term force. Just as important, the term vector field is so intimately tied with the concept of magnetic field that it demands to be included in the lede, IMO.
That being said, the first couple sentences are still the least of the problems that this article still has. It is still too bloated in spots and needs the H-field and magnetization section reorganized somehow, IMHO. I would love to also add a section on the H-field of a magnet, with comparisons between the H and the B fields shapes. I think it is good that we are working on improving the first sentences, but we need to do the same for the rest of the article.
TStein ( talk) 06:43, 9 July 2009 (UTC)
The lede for Electromagnetic field: "The electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field." Vector fields do not arise in that article until well into it, in a section entitled "Mathematical description."
Would the analogous lede here be: "A magnetic field is a physical field produced by magnets and electric currents and is detected by the force it exerts on moving electric charges and magnetic materials."?
If the consensus is that the concept of a vector field must play a part in the lede so be it, but I don't see that it contributes much at that point in the article or that it is required as prelude to what comes after. Likewise I do not think that either dipoles or energy density are critical to any of the TStein's helpful list of lede purposes. Jojalozzo ( talk) 23:43, 9 July 2009 (UTC)
Not to complicate matters (or contradict myself), but the magnetic field is in truth a field (physics), and only in the classical physics approximation is it a vector field. (More accurately, it's a quantum field.) :-)
I'm very fond of the above suggestion, "A magnetic field is a physical field produced by magnets and electric currents and is detected by the force it exerts on moving electric charges and magnetic materials." An inaccurate use of the word "force" is to be avoided if possible, except as a last resort within scare-quotes. :-) -- Steve ( talk) 07:10, 11 July 2009 (UTC)
I think that the type of mathematics required (scalar, vector, tensor) to describe the field should not be a requirement for the first (layperson's) sentence. How about just saying it's a field: "A magnetic field is a field which surrounds magnetic materials and electric currents, and is detected by the force it exerts on other magnetic materials and moving electric charges."? This is what was there before Chetvorno's bold proposal but without "vector".
Or to avoid redundancy: "Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges."
Bowing to the apparent consensus that vector field deserves prominence in the lede, perhaps the second sentence could be "They are described mathematically as vector fields." Jojalozzo ( talk) 01:24, 12 July 2009 (UTC)
Since there seems so much interest in this sentence I thought I would propose a compromise before making the change.
This is essentially combines Jojalozzo compromise with a simplified sentence from magnet. The ref is added as an afterthought and is not the important. The first sentence is somewhat flawed technically in that magnetic fields are detected by more the just torques. Normally, I would be a little bolder, but with so many people interested in this, I thought I'd post it here first. TStein ( talk) 05:24, 13 July 2009 (UTC)
![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 | Archive 2 | Archive 3 | Archive 4 | Archive 5 | Archive 6 |
I am still learning my ropes around the wiki and I appreciate your effort here. Science involves consensus and while a consensus of two isn't very good it beats a consensus of one by quite a bit. Personally, I think that a wiki like this should follow the model used for coding large software projects of having all articles peer reviewed before before committing. As long as you or someone else (and better yet a bunch of people) are willing to help, I will follow that model.
(By the way would it be better to edit your original response or to copy it as in here?)
Anyway, I'm just one guy, and you're welcome to disagree with and ignore any of those suggestions. Also, I don't know if anyone else will offer feedback, you may want to sit on it a few more days before posting, at your discretion. Also, I tend to prefer big all-at-once changes to a zillion small ones, but maybe that's just my opinion.
TStein ( talk) 19:19, 19 May 2008 (UTC)
Here's the link to the page.
Ok, I am almost to the point where I am ready to commit my changes. I dealt with most of the issues that Steve raised. I left a minor issue or two for others to fix. I made some larger changes to the visualizing the magnetic field section. I also got a good start on the H field section. I am not as comfortable with the H field as I would like to be, so help would be appreciated there.
Other problems: I included 2 images as placeholder until better images can be found.
I did not like any of the right hand rule images because most of them had little to do with F = v×B. They mostly had to do with generating current when pulling on a wire. The signs are reversed for these 2 cases.
The second image was an attempt to sketch Earth's magnetic field including a 'magnet' in the interior. I thought it might help people to see approximately where Earth's magnetic field is generated and what is the polarity of that magnet. I found a lot of similar stuff on the web but all of them had the wrong pole of a magnet (N) under Earth's N magnetic field. Unfortunately my attempt had the field lines to rounded, which I could fix if I had the time. Worse, the arrow heads that show up on my svg viewer fx 2.0 are not showing up on wikipedia's viewer.
TStein (
talk)
05:57, 23 May 2008 (UTC)
Incarnation seems to me a poor word choice. It means in the flesh, kind of like when a god becomes human. I'll think of a better word. Daniel.Cardenas ( talk) 14:53, 23 May 2008 (UTC)
I saw this fifty-minute NOVA documentary that addressed the problems our magnetic field has -- it's getting less and less powerful by the day. Some say it's just a normal 10,000-year cycle from which the source of magnetism will change direction. Basically, said in everyday language - "south" becomes "north" and vice versa. As the transicion will occur, it is expected a 10% increase of people with skin cancer. Now, does anybody think we should add this piece of information?
-- 96.232.60.47 ( talk) 21:09, 28 May 2008 (UTC)
There is still a lot of work that has to be done in cleaning this article up. There were some problems introduced, such as with the 3 figures I added. (Magnetic field with compasses, right hand rule and Earth's magnetic field.) Overall, though I think it is a large enough improvement over the previous case to justify the edit.
The main reason I am doing this, though, is to avoid the difficulties in keeping my branch in synch with the article. Plus I am hoping to get more eyes on this page.
Still needs:
I am willing to push this article forward as far as I am able. Right now I need more eyes on the problem, though. Personally, I think this can and should be pushed to being a FA.
TStein ( talk) 16:56, 2 June 2008 (UTC)
Pol098 has just put in a paragraph differentiating between the "magnetic field" and the "electromagnetic field", in particular saying that the latter is only associated with electromagnetic radiation. I don't think that's right. I think the "electromagnetic field" is just the electric field and the magnetic field put together into two words. A magnet does have an electromagnetic field: its electromagnetic field consists of zero electric field and whatever magnetic field.
I don't have a textbook on hand to confirm this, but one piece of evidence is that the so-called " electromagnetic field tensor" (which, one would think, should describe the electromagnetic field) includes any magnetic and electric fields, not just those that make up EM waves. In particular, the electromagnetic field tensor (and hence, I think, the electromagnetic field itself) is certainly not zero around a stationary magnet.
Or maybe I'm way off. What do other people think? Can anyone find reliable sources on this? -- Steve ( talk) 20:28, 29 August 2008 (UTC)
I am trying to do a back-of-the-envelope calculation and navigated to this page for a definition of B and H fields. The page fails to cover these very fundamental in anything approaching clarity. The B field defintion is turgid and buried halfway down the page. The H field definition is more alluded to than buried. ~Paul V. Keller 16:25, 1 January 2009 (UTC)
I have objections with the following statement as being misleading:
It is true that starting from a pure Electrostatic term one can arrive at the above statement. It is also true that all of Maxwell's equations can be derived from Coulomb's Law (with some difficulty). (One has to be careful, amongst many other things, not to also 'prove' that gravity follow Maxwell's equations as well.) The first problem I have is that, as far as I can tell, there is no reason to assume there is one reference system that is purely electrostatic for real systems of charges. A more important pedagogical reason is that there is no reason to favor the Electric field in this way. In relativity, boosting a pure electric field will result in an electric plus a magnetic field, true. It is also true, though, that boosting a pure magnetic field will result in a magnetic field plus an electric field!. There is no a priori reason to think that the electric field is any more fundamental then the magnetic field. Advanced theories all treat E and B on equal footing. (Together they form an anti-symetric 4-tensor).
All of this is covered above from the last time that this type of statement was placed in this article. The end result was that the sentence was altered to be more technically true from the above perspective. This process already been done at least twice and vestiges from this slow motion edit war can be found sprinkled through the article.
This article is already polluted enough. As an example of this see the section directly above this one on this discussion page. (Unfortunately, I myself have contributed a good portion of that pollution as I have strugled to learn how to write encyclopedia articles well.) I was hoping that we can reach a consensus so that we can stop the madness. TStein ( talk) 15:44, 23 January 2009 (UTC)
There seems to be too much in this article about the difference between B and H. The two are related by the simple equation B =μH where μ is the magnetic permeability. B is the magnetic flux density which depends on the permeability of the medium. In Maxwell's books the permeability would be a measure of the density of magnetic field lines for a given magnetic field strength H.
B is essentially a weighted version of H which seems to make it a more useful quantity. Maxwell tended to use the product μH. I can't think that there's much more that needs to be said about the inter-relationship between these two quantities. I might want to take everything out regarding B and H, and put this short paragraph in instead. David Tombe ( talk) 20:56, 28 March 2009 (UTC)
Steve, In a bar magnet and all ferromagnetic materials, μ is huge. Therefore B will be huge even if H is small. I cannot believe that the magnetic field strength H is precisely zero inside a bar magnet. That wouldn't make any sense. There has to be a magnetic field inside a bar magnet. Who told you that there is no magnetic field H inside a bar magnet? David Tombe ( talk) 17:16, 29 March 2009 (UTC)
Steve, There is still a magnetic H field present when hysteresis takes place in a bar magnet. Hysteresis is a topic similar in principle to when Hooke's law breaks down due to elastic deformation. You are quite entitled to write a section on hysteresis. My point was simply that B =μH is the general rule, as like Hooke's law, and that there is an awful lot of unnecessary discussion in the main article about the distinction between B and H. I explained that distinction. Why do you need to bring hysteresis into it? It's like having endless discussion about the difference in meaning between 'Force' and 'extension' in Hooke's law. Someone points out Hooke's law as F = -kx and then you come along and introduce cases where Hooke's law breaks down due to the elastic limit having been reached. David Tombe ( talk) 23:15, 29 March 2009 (UTC)
Steve, I wasn't saying that force is the same as extension. I was making the analogy between 'Force' and H on the one hand, and between 'extension' and B on the other hand. It is by no means a perfect analogy. I was merely using a cause/effect analogy to make the point that in an encyclopaedia, one begins with the most basic general rule.
Hysteresis is a specialized topic, not fully understood, and which involves a certain amount of shielding and delayed reaction as between cause and effect.
In principle, B =μH as a general rule. There are far to many instances on the main article of people trying to learn this general rule on the job. It could be grossly simplified. Then if you want to write about Hysteresis, feel free to do so. David Tombe ( talk) 21:28, 30 March 2009 (UTC)
In order to make at least a first stab to address the problems of the relationship between B and H, I made a number of small changes that I hope are in the right direction. (Although, I think the net effect is to increase the size of the article :( ). First of all I added the linear relation B = mu H to a number of different locations that should have already have it. I tried to emphasize the importance of that equation even while stating directly what the problems were. Second I tried to clarify the difference between B and H and hopefully made it a little more evident why this is important.
The second step is far from complete. I also realize that there is a difference in how physicists (like myself) approach this then how engineers approach it. The B vs H section is written from the physicists perspective. I have tried to respect the engineer's approach by making this section as short and as clear as I can (at this point) while keeping the fundamentals that are necessary from the physicist's point of view. There is still work to be done there, though I think that it is much better from my point of view. TStein ( talk) 16:17, 31 March 2009 (UTC)
Tstein, you're learning. The next stage is to see if you can explain displacement current in a way that fits with the EM wave equation, without using the aether.
Meanwhile, I think we are stuck here with no choice but to list B = μH as an accepted fact of which the explanation which existed in the 19th century is now denied. There is no existing explanation, and that is what has caused all the confusion on the main article. Relativity cannot explain μ. The equation which Stannered mentioned above is merely an extension of the basic equation. David Tombe ( talk) 13:16, 1 April 2009 (UTC)
Tstein, I have no quarrel with the existing equations. But from what I can see, the original meaning of the relationship B = μH was lost when Maxwell's vortex sea was abandoned. Nevertheless, I agree that B is by far the more useful quantity, and indeed in most of Maxwell's writings, he uses the product μH. From what I can see, M is to atomic and molecular matter, what H is to the abandoned vortex sea. And becuase the vortex sea has been abandoned, nobody knows how to explain the meaning of H. All they know is that it fits into the maths.
For Maxwell the quantity corresponding to H was more accurately the circumferential speed of one of his molecular vortices. This circumferential speed is what contributed to the pressure between adjacent magnetic lines of force, and hence caused magnetic repulsion. The vortices were aligned solenoidally along their rotation axis, and as you know, the magnetic field lines between like poles spread outwards in the space between the poles, and come together laterally. Maxwell ascribed the magnetic repulsive force to centrifugal force in the equatorial plane of the vortices. The circumferential speed of the vortices was a measure of their vorticity, and so H can be seen as a measure of the vorticity of a single magnetic line of force. With the μ term added, we then obtained a kind of magnetic flux density B, because μ was considered to be related to the density of the vortex sea. Hence B is magnetic flux density and it is equal to μH, where H is a measure of vorticity or magnetic field strength. The modern definition of H is purely mathematical, and so it will be very hard to ascribe a physical significance to it in the absence of Maxwell's vortex sea. David Tombe ( talk) 19:08, 13 April 2009 (UTC)
Since this article has finally gotten some of the attention it deserves with more then one active editor I thought it prudent to discuss possible large scale changes to avoid butting heads.
Issue 1: large scale reorganization. A while back I reorganized this article to enumerate the field sources together and then the elementary effects together. This brings me to Brews Ohare's edit to magnetic dipoles. At first I was mildly annoyed that Brews Ohare included information about how magnetic field affected the dipole with a torque in the dipole as sources of B field section. Then I realized that splitting up the dipole interaction into 2 sections one for creation of the field and the other for interaction may have hurt the article. I liked what Brews Ohare did there. Maybe it is more important to organize both dipole sections together (creation of B and interaction with B) and do the same for both magnetic field and currents sections, etc.
Issue 2: In my opinion we need to keep permanent magnet section near the very top and separate from magnetic dipoles. My main reason for this is that all articles have to start with the simple and familiar before going to the more complicated and unfamiliar.
Issue 3: In my opinion we need to keep the magnetic field lines and visualizing them section near the very top just after the discussion of the permanent magnets (including compasses). In particular the section on magnetic fields alwas comes in loops sets up a lot of the understanding that is needed for later. Plus people should be fairly familiar with seeing field lines.
Issue 4: Consistency with the level of complication. What level of detail are we looking for here? Right now we have the Landau-Lifshitz-Gilber equation but not the Biot-Sarvart Law nor Maxwell's equation. If we included every equation at the level of L-L-G would we have enough room for the article to be qualitative? In my opinion an article like magnetic field needs to be simple with links to the more in depth stuff. Alternatively every section could start off simple then work toward the complex. Having the article with a repeating patern of easy to complex, easy to complex sounds like a way to lose everyone, though. Then again I don't claim to be an expert in that matter.
Issue 5: When to use magnetic field and when to use magnetic B-field is a question that Brews Ohare brought to my attention by his edits. After some thought I am convinced that we should use magnetic field (implying both B and H) for any source of magnetic fields, BUT I think we should use the magnetic-B field for any affect. The magnetic-H field is largely a theoretical construct that has no effect on anything. It cannot be directly measured typically. It is the magnetic B-field that pushes stuff around.
I hope this gives a good indication of my thoughts at least so that we can come up with a good solution and really make this article shine. TStein ( talk) 21:25, 3 April 2009 (UTC)
It seems the article often used the constructions "magnetic B-field" and "magnetic H-field"; I have tried to eliminate the word "magnetic" in these combinations, as it seems to contribute nothing. Brews ohare ( talk) 17:18, 7 April 2009 (UTC)
Are we then going to leave it that Poisson's great approach relating to B and H, which worked so well, only worked by coincidence even though it was wrong? That's what it says in the main article. What about wording it more neutrally, something along the lines of, 'despite the success of Poisson's approach, it is no longer accepted in modern physics, and no alternative approach has yet taken it's place?'.
As regards Maxwell, there are a few inaccuracies in the article. You will have a hard job finding any references to electric charge in Maxwell's 1861 paper. The closest that he comes to it is with 'density of free electricity'. Maxwell tends to work in terms of force per unit volume, with the volume term incorporated into a kind of density term. The density term corresponds reasonably closely with the modern day charge to mass ratio, and so his electromotive force terms tend to correspond to 'electric field'. David Tombe ( talk) 12:29, 17 April 2009 (UTC)
I'll try. But from what I can see, the modern explanation is nothing more than a mathematical definition. I could probably fix up the bits about what Maxwell said and then leave it for somebody else to do the rest. David Tombe ( talk) 14:12, 18 April 2009 (UTC)
Presently, the history section reads too objectively, I think. Rather than, "this approach was wrong," we should suggest that modern science offers a more complete alternative theory. The current theory appears to be valid, but we certainly don't know that it's "correct." -- Jeff Wheeler ( talk) 03:56, 23 October 2009 (UTC)
This topic is a delicate one, as reading the talk pages at Faraday's law of induction will illustrate. The main problem is that Faraday's law in terms of flux density covers both motional and transformer EMFs, and of course both have enormous practical use in motors and generators. However, the Maxwell relation using curl E that is one of Maxwell's equations does not include motional EMF, and so is not equivalent to the first law, although often referred to as Faraday's law nonetheless.
Including the motional EMF makes for a a complicated equation. One has several options here: (i) put in the gory details (ii) leave out all the equations and stick to words (iii) keep the flux density equation and dump the partial DE using curl (iv) try to cover the matter at several levels by putting in enough verbiage to cover things for the casual reader, but retaining the mathematical expression.
Further revisions of the section Magnetic_field#Electric_force_due_to_a_changing_B-field may be advisable, but it requires some care Brews ohare ( talk) 06:25, 3 May 2009 (UTC)
There is no "controversy" here. The distinction between motional and transformer EMF is real and well-documented. It prompted some of EInstein's thought about relativity and formed the preamble to one of his famous papers. It has been remarked upon by Feynman (see the Faraday's law of induction article). It has very noticeable practical consequences.
Two usages of "Faraday's law" are in the literature. This kind of multiple usage occurs all through physics, and often seems to lead to sides being taken about who is "right". The real point is that Faraday's law of induction is a significant topic and covers two phenomena while the Maxwell-Faraday equation covers one of the two. So what do you want to do? I'd say cover both.
I think your statement : "The way I see it, we can either deal with every petty 'controversy' about naming conventions or we can write a great article." is wide of the mark. Brews ohare ( talk) 21:43, 4 May 2009 (UTC)
I have attempted to simplify this discussion using some of your suggestions. Brews ohare ( talk) 22:52, 4 May 2009 (UTC)
This article seems rather long. Suggest shortening. For example history of B and H to be moved mostly to sub article. Other sections towards the bottom of the article that already have subarticles should be shortened to a paragraph. What do you think? Daniel.Cardenas ( talk) 04:57, 28 May 2009 (UTC)
I think I saw on wikipedia a comparison of different magnetic field strengths. Does someone know where that is at? Should we put it in this article? Thx, Daniel.Cardenas ( talk) 04:57, 28 May 2009 (UTC)
(UTC)
Why isn't there a differential form of the magnetic field such as:
For a line current? I think those let you see very easily the connection to the rotational form in Maxwell's equations. —Preceding unsigned comment added by 169.198.254.6 ( talk) 14:38, 12 June 2009 (UTC)
I removed the following because I could find nothing to support it:
The magnitude of B is defined (in SI units) in terms of the voltage induced per unit area on a current carrying loop in a uniform magnetic field normal to the loop when the magnetic field is reduced to zero in a unit amount of time.
The best I could find is that (conceptually) the Weber is defined by the flux law, while Tesla is defined conceptually as a Weber/square meter. In practice, the unit of Tesla is typically determined using properties that are way beyond the scope of the article. The B fields has many potential definitions based on its effects and it seem superfluous to chose one that is not even used in practice to set the standard for how to measure the unit.
Are there any 'official' definitions of B or H out there? TStein ( talk) 21:36, 12 June 2009 (UTC)
The first thing the reader is told is that a magnetic field is a vector field. Not only is this meaningless to most readers but a) appears to avoid the task of defining the topic and b) sounds a lot like mistaking the map for the territory. Some of you may be so immersed in the theory that you have difficulty explaining the phenomena in plain language. This is not anywhere near my area of expertise but how about something like this: "Magnetic fields are a cloud of forces that surround magnetic materials and electric currents. These forces can be detected by their interaction with the magnetic fields of other magnetic materials and electric currents."? Jojalozzo ( talk) 19:52, 8 July 2009 (UTC)
The enterprising lay reader who can get past the first sentence, will find "dipole" introduced in the second without any explanation, not even a responsibility-avoiding link. The only people who are likely to understand this introduction already understand enough to skip it. This article would be much improved if the intro gave non-experts a good idea of what is known without them having to refer to other articles or reference materials. Jojalozzo ( talk) 20:08, 8 July 2009 (UTC)
I would love to make the first sentences more accessible and those terms used too early bothers me as well, but I have not seen a better alternative. One thing we have to keep in mind is that the lede section is not an introduction. The lede section has to do several (seemingly mutually exclusive) things:
We should always strive for the third, but we have to be careful not to sacrifice too much of the first and the last. Using technical terms in the lede does not bother me too much provided that they are explained in the article and that they are directly related to the subject of the article. The term vector field fits both of these dipole probably does not.
All of the above examples, so far, have failed to be reasonably technically correct; in particular, they grossly misuse the term force. Just as important, the term vector field is so intimately tied with the concept of magnetic field that it demands to be included in the lede, IMO.
That being said, the first couple sentences are still the least of the problems that this article still has. It is still too bloated in spots and needs the H-field and magnetization section reorganized somehow, IMHO. I would love to also add a section on the H-field of a magnet, with comparisons between the H and the B fields shapes. I think it is good that we are working on improving the first sentences, but we need to do the same for the rest of the article.
TStein ( talk) 06:43, 9 July 2009 (UTC)
The lede for Electromagnetic field: "The electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field." Vector fields do not arise in that article until well into it, in a section entitled "Mathematical description."
Would the analogous lede here be: "A magnetic field is a physical field produced by magnets and electric currents and is detected by the force it exerts on moving electric charges and magnetic materials."?
If the consensus is that the concept of a vector field must play a part in the lede so be it, but I don't see that it contributes much at that point in the article or that it is required as prelude to what comes after. Likewise I do not think that either dipoles or energy density are critical to any of the TStein's helpful list of lede purposes. Jojalozzo ( talk) 23:43, 9 July 2009 (UTC)
Not to complicate matters (or contradict myself), but the magnetic field is in truth a field (physics), and only in the classical physics approximation is it a vector field. (More accurately, it's a quantum field.) :-)
I'm very fond of the above suggestion, "A magnetic field is a physical field produced by magnets and electric currents and is detected by the force it exerts on moving electric charges and magnetic materials." An inaccurate use of the word "force" is to be avoided if possible, except as a last resort within scare-quotes. :-) -- Steve ( talk) 07:10, 11 July 2009 (UTC)
I think that the type of mathematics required (scalar, vector, tensor) to describe the field should not be a requirement for the first (layperson's) sentence. How about just saying it's a field: "A magnetic field is a field which surrounds magnetic materials and electric currents, and is detected by the force it exerts on other magnetic materials and moving electric charges."? This is what was there before Chetvorno's bold proposal but without "vector".
Or to avoid redundancy: "Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges."
Bowing to the apparent consensus that vector field deserves prominence in the lede, perhaps the second sentence could be "They are described mathematically as vector fields." Jojalozzo ( talk) 01:24, 12 July 2009 (UTC)
Since there seems so much interest in this sentence I thought I would propose a compromise before making the change.
This is essentially combines Jojalozzo compromise with a simplified sentence from magnet. The ref is added as an afterthought and is not the important. The first sentence is somewhat flawed technically in that magnetic fields are detected by more the just torques. Normally, I would be a little bolder, but with so many people interested in this, I thought I'd post it here first. TStein ( talk) 05:24, 13 July 2009 (UTC)