Talk:Magnetic field/Archive 1

message: Thanks, I see now that a sketch of a thought experiment has been added to the article.  Something still confuses me though.  In the thought experiment, call the first observer A (i.e. the observer that is "stationary") and the second observer B (i.e. the observer moving with the lines of charge).  The current description points out that, from A's point of view, B's clock ticks more slowly, thus A perceives the net force F_A between the lines of charge as weaker, i.e. F_A < F_B.  This weakening corresponds to the magnetic field that A perceives, attracting the moving lines of charge and opposing the repulsive electric force.  However, couldn't we also change our perspective to that of B, and say that from B's perspective, A's clock ticks more slowly, thus we should expect F_B < F_A ?  Surely there's something basic about special relativity that I don't understand.  We can't have both F_A < F_B and F_B < F_A.  MichaelMcGuffin 18:01, 8 Dec 2004 (UTC)
thread_title:  First mention of the thought experiment 

message: "moving electric charges (electric currents) that e"
:One thing I guess I never learned.  Because of relativity, don't we need to specify what the particles are moving relative to?  Do they not see each others magnetic field if they are not moving relative to each other?  I guess they would behave as if they were only electrostatically repelling or attracting each other?  Oh man, now I have confused myself...  - Omegatron 23:41, Apr 25, 2005 (UTC)
::This is why the presence of a magnetic field depends upon your frame of reference.  Consider a charged particle moving at a constant velocity (i.e. in an inertial frame).  If I am in an inertial frame of reference where the particle is moving with respect to me, I see a magnetic field.   If I am in the same inertial frame as the particle, so that it is at rest with respect to me, I see no magnetic field.  In general, when you change frames of reference, magnetic and electric fields get mixed up (together, they form a rank-2 tensor).  —Steven G. Johnson 02:04, Apr 26, 2005 (UTC)
::'O', the bottom line is that magnetic effects are a result of special relativity.  That is, if you start with Coulomb's Law and then impose Lorentz invariance (or is it covariance?), you get magnetic effects. It turns out that there is an analog to magnetism in gravity - so called gravito-magnetism.  I think it is also called 'frame-dragging'.Alfred Centauri 12:39, 2 September 2005 (UTC)
thread_title:  moving with respect to what? 

message: I've added a little item about the orientation markers vs actual field flow. I've been unable to find anything that says if the magnetic field lines actually move or if they are simply static lines through space. (The arrow is just a reference to mark field orientation, as far as I've been able to determine.)
:They don't move. In fact, they don't even exist, see below. -- Tim Starling 12:32, Jun 24, 2005 (UTC)
I'm not a professional physicist by any means, but I've also never determined if the field actually exists as separate concentrated lines/shells as iron filings demonstrate, or if the lines form only as a RESULT of the iron filings being there, building up into thicker lines as more iron filings enter the field. Is a magnetic field in empty space "ridged" as the filings suggest, or is a field in open space simply an even undifferentiated gradient from strong to weak? DMahalko 09:31, 24 Jun 2005 (UTC)
replies: text: Field lines are just diagrammatic. The number drawn in any given diagram is arbitrary, the field is smooth, not ridged. Lines are just one way to show the direction and magnitude of a vector field at every point on a plane. Iron filings tend to mimic the shape of diagrammatic field lines, because adjacent lines of iron filings tend to repel each other, and because grains that are in contact tend to line up end-to-end with unlike poles touching. -- Tim Starling 12:32, Jun 24, 2005 (UTC)
This particular explanation needs to be included in the main text.  It also should delve cautiously into more fundamentally what the field may consist of (e.g. alignment/coherence of virtual photons or e/p pairs from the vacuum, conceptual vortex mechanisms versus vacuum "permeability" changes leading to repulsion/attraction, etc (never liked the descriptions using compression of field lines/rubber bands for attraction). (Dfwrunner 20:54, 8 June 2007 (UTC)
thread_title:  field line flow? field shells in open space? 

message: To find a way out of the impasse thus far, I propose that we have Reddi put his material for rotating magnetic fields into rotating magnetic fields, in place of the redirect.  The concept isn't important enough for the space taken up in magnetic field, but it is true that a rotating magnetic field is a concept, independent of its applications, and that it could be useful.  It might end up being a longer article than I would have written, but I don't think of that as a realy problem.  But we certainly need a consensus somehow... thoughts?  -- SCZenz 20:00, 27 July 2005 (UTC)
replies: text: A rotating magnetic field in of itself is not special, its useful though its applications. I suggest that this text be added to the Motors article under AC motors, since there is a small history section there already which could be expanded. Salsb 20:05, 27 July 2005 (UTC)

text: What I'd consider even better,  if Reddi would take the text on rotating magnetic fields and expand it into an article on the history of electric motors, that would be very cool indeed. Although admittedly a fair amount of work. Salsb 20:09, 27 July 2005 (UTC)
replies: text: That sounds interesting ... I have been aquiring much of Edison's patents and Tesla's patents (as well as others). Alexanderson (sp?) built huge machines ...and this would include the early work in electrostatic machines. I'll kick this history of electric motors around in my head abit. Sincerely, JDR 18:19, 8 November 2005 (UTC)
thread_title:  Rotating magnetic field proposal 

message: :
\mathbf{B} = \frac{\mu_0}{4 \pi}\frac{q}{r^2}\mathbf{\hat r} \times \mathbf{v}
is this equation right, or should r hat and v be switched (in the cross product). Cause i just had a physics HW problem that contradicted. Still doing the HW, so don't have time to check up on anything. User:Fresheneesz
:The Biot-Savart Law is usually applied in differential forms, like in the following two expressions:
::
\mathbf{dB} = \frac{\mu_0}{4 \pi}\frac{dq}{r^2}\mathbf{v}  \times \mathbf{\hat r}
::
\mathbf{dB} = \frac{\mu_0}{4 \pi}\frac{i}{r^2}\mathbf{ds}  \times \mathbf{\hat r}
:This law is important in studying magnetic fields. May somebody please add more detail about that in the article? Thanks. - Alanmak 23:35, 12 February 2006 (UTC)
replies: text: Yes, I agree with you. I am not a wikipedia user myself so I am not going to do any kind of correction or whatever in this article, but a friend of mine called me  and asked me to explain some magnetics because she was trying to get some general idea first using this article before starting serious studies usin textbooks. When she showed me, I could immediately understood the source of her confusion. This article is too focused in relativity and simply ignore the basics like Gauss' Law and Biot-Savart Law. They have very significant practical and historical value, the second Maxell Equation is the Gauss Law, not that formula derivated from the Lorentz Transformation. By the way, the Gauss Law, in its both "shapes" have more practical value than the Lorentz transformation. If I wasn't an engineer I wouldn't understand more than a half of information in this article. This article is in an Encyclopedia and should not be just a badly-done gathering of formulas. Who ever wrote this article, if you think you are cool showing far too advanced formulas and definitions, then you are very wrong. No wonder why wikipedia is not respected in serious academic environments. —The preceding unsigned comment was added by 222.150.226.168 (talk) 14:21, 13 April 2007 (UTC)
thread_title:  Question of validity - biot savart law 

message: I suggest that the picture does not show the magnetic lines of force due to an 'isolated' magnet. What it shows is the magnetic lines of force with a lot of iron filings scattered in the magnetic field. The picture is therfore misleading in that if you plotted the field lined using one tiny isolated bar of metal, the pattern you would get would not be the same as that shown! Comments?
--Light current 18:20, 12 April 2006 (UTC)
thread_title:  Iron filings pic. 

message: If the presence of a dielectric (E >1) can distort an electric field, does the presecnce of a ferromagnetic material (U>1) distort a magnetic field from a magnet. If so, what do iron filings do to the magnetic filed lines when spread around a bar magnet? 8-?--Light current 00:12, 4 May 2006 (UTC)
replies: text: Yes. The field lines are nearly perpendicular to the surface of a high permeability material. Madhu 14:36, 10 August 2006 (UTC)

text: Here's an image of distorted field lines. It's not great, but it's the first one I could find quickly. Of course, iron filings are usually light enough to be shifted by the field of a typical bar magnet, so each affects the other. If the iron filings were not permitted to move (or the field strength was not sufficient to move them), the field lines would follow the filing, rather than the other way around. Think about the field lines within an iron core transformer. Without the core, the field lines would be all over the place :-( Madhu 04:29, 11 August 2006 (UTC)
thread_title:  Electric and magnetic fields- whats the difference? 

message: um...this is the left hand rule, no? reverse thumb vector...Gatoatigrado 03:32, 6 June 2006 (UTC)
replies: text: No that picture is of the right hand rule. For magnetic fied, if the current flows in the direction of your thumb, the magnatic field goes in a circular path in the direction of your fingers. You need to make a kind of thumbs-up sign with your right hand for that. The left hand rule is motion of charged particles. --H2g2bob 16:21, 6 June 2006 (UTC)
thread_title:  Right hand rule 

message: I know that many objects are not magnetic (i.e. wood) but magnetic fields still go through them.  For example when you place a metal object behind a thin piece of wood and place an attracting magnet on the other side, the force pulling them together is the same as it would if there was nothing in between them(given they were the same distance appart).  So the magnetic field goes through these things, is there anything that magnetic fields do not pass through?
So basically an easy way to understand would be: if there was a strong magnet in the center and you surrounded it behind a wall of substance X which then makes it so nothing outside the wall would feel any pull from the magnet inside.  Is there any such substance?
Thanks 
~Matt
Email, Demostheness@hotmail.com
:See  http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29 and mumetal.--Light current 11:32, 5 August 2006 (UTC)
replies: text:  A superconductor (read Meissner effect) will block a magnetic field up to a limit depending on the material the superconductor is made from and its temperature.  Conductors will dampen changes in the magnetic field flowing through them as the changes induce a current which in turn induces a magnetic field which perfectly opposes the applied field change.  This is very short lived as the currents induced die away due to resistance in the material and so stop blocking the field.  Its still worth knowing about becuase it leads to Inductance and a few effects to do with fluctuating magnetic fields CaptinJohn 11:15, 13 March 2007 (UTC)
thread_title:  Can anything block magnetic fields? 

message: Hello. I came to this page hoping for an intuitive explanation of the measure B of an electic field, but I can't find one. I have searched the web for several hours and I still can't find one.
The measure E of an electric field make sense to me, the amount of force in the direction of E, per unit of charge of a test charge placed in the field. However B is a bit of a mystery. 
Why didn't physicists define B as being in the direction of the force as well - something like force in the direction of B per unit charge per unit velocity. It seems a bit ugly to me to have the force of an electric field with E, but the force of the magnetic field is at right angles to B. I'm sure there is a deep reason for it, but I don't see it. It would be helpful, on this page, to have an intuitive explanation of exactly what B is in a physical sense, and why it is at right angles to the velocity of the test charge and the force on the test charge. Can anyone please enlighten me? 
Nicolharper 16:33, 9 August 2006 (UTC)
replies: text: The difference is that electric charges move in the direction of E and magnetic domains line up in the direction of B. I believe magnetic field lines were theorized based in orientation of other magnets or iron filings within a B field. Michael Faraday, James Clerk Maxwell, and others observed and formalized the relationship between moving charges and magnetic fields. It wasn't planned, it was discovered long after magnetism was observed. I guess it would possible to redefine B in the direction of a moving charge, but then it would be at right angles with intuitive notions of field lines based on simple experiments with a compass or iron filings. Madhu 14:32, 10 August 2006 (UTC)
replies: text: Thanks. Much appreciated. It would be good if this could be explained in the article. Maybe I'll do it if I find time. Nicolharper 15:38, 10 August 2006 (UTC)
thread_title:  Intuitive explanation of B 

message: I noticed this bit in the section about energy density :
<<
For example, a magnetic field B of one tesla has an energy density about 398 kilojoules per cubic metre, and of 10 teslas, about 40 megajoules per cubic metre.
This is the same as the pressure produced by magnetic field, since pressure and energy density are essentially the same physical quantities and thus have the same units. Thus, a magnetic field of 1 tesla produces a pressure of 398 kPa (about 4 atmospheres), and 10 T about 40 Mpa (~400 atm).
>>
Does anyone understand what this means about pressure, as a physics PhD student i  just dont get what its on about.  Pressure on what? Physical pressure? what does it mean?  A magnetic field on its own does not exert pressure it only exerts pressure on a magnetic substance inside the magnetic field and then the force is proportional to the field gradient, not field strength.
Any comments.
: This was supposed to be force (or pressure) on ferromagnetic materials as described in slightly greater detail in the electromagnet article. The old section included a complete, but short derivation. Since then, it has been edited to the point where it no longer appears to make sense. I'm not completely sure why it was whittled down, but you are welcome to improve it. Madhu 23:02, 12 September 2006 (UTC)
thread_title:  What is all this about pressure?? 

message: The diagram showing the magnet and iron filings is not acuate for when you use an electromagnet
http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Graphics/coil1.gif
Also magnetic feilds can be alternating by using an electromagnet and alternating current insted of direct current
Does anyone know much about the effects of AC magnetic feild's? Im esspecally intrested in verry high frequencies Alan2here 15:15, 1 October 2006 (UTC)
replies: text: I Know that alternating magnetic fields are very difficult to generate at high frequencies.  This is because to alternate : I Know that alternating magnetic fields are very difficult to generate at high frequencies.  This is because to alternate the field requires you to dump all the energy in that field.  If you look at the above numbers (I'm not sure they are correct but I have no reason to doubt them) then to make a 1000cc (a 10cm cube) volume field of 1T oscillate at 1kHz would need a 400kW of power to be generated and dumped.  The problem you have is that it would also need a lot of very thin wire wound very tightly to actually generate the field.  The wire would melt very easily if not cooled and what is difficult to do.  I ran a 1T water cooled magnet in DC (direct field) mode when I did my masters and it took about 5 minutes to get it up to 1 T because if you went any faster it burned out.  So with our cooling system (which was huge) we could have had a 1T field oscillate at 0.833mHz (one cycle per 20mins).  On that basis Id say it is the cooling system that limits suck work.
I should note here that the magnet I used was NOT superconducting.  It you use a superconducting magnet that power is dumped in the power supply rather than the coils so its easier to cool but I think you still have the same problem of needing ever bigger cooling systems to run even small, low frequency fields.  CaptinJohn 11:31, 13 March 2007 (UTC)
thread_title:  Magnetic Field's 

message: The lead stated:
:In physics, a magnetic field is that part of the electromagnetic field that exists when there is a changing electric field. A changing electric field can be caused by the movement of an electrically charged object, as in an electric current; or a combination of the orbit of an electron around an atom and the spin of electrons themselves, as in a permanent magnet.
That was just completely wrong. A constant electric current, for example, does not create a varying electric field, but it does create a magnetic field. There are two physically distinct mechanisms for creating a magnetic field, which are expressed by two separate terms in Maxwell's equations. I've fixed the error.--24.52.254.62 04:54, 2 November 2006 (UTC)
replies: text: Still somewhat of an error in "a magnetic field is that part of the electromagnetic field that exerts a force on a moving charge."  Particles with spin can have intrinsic magnetic moments, and thus interact with a magnetic field. A point particle with spin isn't quite the same as a moving charge.  Glancing through the article I see that the explanation section needs serious work.  (There seems to be some confusion between the electric field and the electromagnetic field.  Also, it implies that the electromagnetic field has a non-relativistic portion?) --Starwed 07:50, 2 December 2006 (UTC)
thread_title:  major error in lead 

message: I Think A Clen Up Of This Article Should Be Ordered. Meanwhile, can anyone suggest other articles???
—Preceding unsigned comment added by 89.241.123.153 (talk • contribs) 
: Yeah, it could probably do with a bit of a review. Meanwhile..., other articles for what? --h2g2bob 19:58, 21 November 2006 (UTC)
thread_title:  Clean Up Is Required 

message: To me, this section seems like it could be unclear or misleading.
:Einstein explained in 1905 that a magnetic field is the relativistic part of an electric field.
This makes no sense as written.  If the magnetic field is the "relativistic part", what is the nonrelativistic part of an electric field?  I would prefer to say that both are components of an electromagnetic field.
It's true that the magnetic force between two moving charges can be deduced from their interaction in one particles reference frame and special relativity.  That's an entirely different matter than the magnetic field being "part" of the electric field.
:One of the products of these transformations is the part of the electric field which only acts on moving charges — and we call it the "magnetic field".
Again, this isn't how the issue is normally presented.  The author of this section seems to be using the phrase "electric field" to refer to what is more commonly called the Electromagnetic field.  Even if this is valid terminology in some literature, it isn't what's used elsewhere on wikipedia and should definitely be avoided.
:The quantum-mechanical motion of electrons in atoms produces the magnetic fields of permanent ferromagnets. Spinning charged particles also have magnetic moment.
This phrasing makes it seem like the particles are always physically spinning on some axis, which of course isn't necessarily the case.  I would also say that the phrase "quantum-mechanical motion" should link to the article on Spin (physics), rather than the word spinning.
:A magnetic field is a vector field: it associates with every point in space a (pseudo) vector that may vary through time. The direction of the field is the equilibrium direction of a magnetic dipole (like a compass needle) placed in the field.
Currently this is simply a one liner; it doesn't seem to belong in this section.  Perhaps a broader description of how the magnetic field behaves under transformations should go here?
:We use the symbol \vec{B} for the magnetic field and for the sake of mathematical simplicity (one symbol instead of seven).
I'm probably missing something here, but what are the seven symbols referred to?  I know a previous version of this section discussed writing the magnetic field as combinations of the electric field and velocity; is this an orphaned ref. to that?  Also, the text following this statement is just a general discussion of the meaning behind the magnetic field vector, which is needed somewhere in the article, but probably in a more general section.
My thoughts are as follows:
*Details of the relativistic transformation of the electric field into the magnetic are not needed in this article; they belong at Electromagnetism and related pages.  
*The section should be renamed, and be devoted to briefly explaining the role of the magnetic field in "advanced" theories like relativity and QED.
*Some of the content in this section belongs in a more general dicussion of the properties of the magnetic field; conversely, the entire introduction to the properties section is actually about special relativity.  It would be nice if some dicussion could happen on this talk page about exactly how the article should be laid out!
--Starwed 12:04, 23 February 2007 (UTC)
thread_title:  Extension to theory of relativity section 

message: it must have been a spurious "paste", but i do not know how it happened nor how i didn't see it afterward. r b-j 06:30, 10 April 2007 (UTC)
thread_title:  thanks to anon 132.236.59.30  for fixing spurious duplication from me. 

message: This quote is taken from the main article,
 
"Einstein explained in 1905 that a magnetic field is the relativistic part of an electric field". 
The main article then goes on to say that the magnetic field arises as a by-product of the Lorentz transformations.
However, the Lorentz transformations as applied to electric and magnetic fields already include the inter relationships determined by Maxwell's equations. The magnetic field therefore already exists independently of relativity or Lorentz transformations. We cannot therefore state that magnetism is a relativistic effect of the electric field under a Lorentz transformation.
It would be more correct to state that Einstein's Theory of Relativity effects the magnetic field relativistically, but that the magnetic field as affected relativistically doesn't differ in nature from the classical magnetic field. 
If we were to suggest that the classical magnetic field was merely an effect of coordinate frame transformation, this would be tantamount to suggesting that the magnetic field is only fictititious. 
The magnetic field is clearly a different concept altogether from the electric field. The electric field measures force per unit electric charge. The magnetic field, whatever it is, doesn't even have the same dimensions. (58.10.102.2 15:12, 29 April 2007 (UTC)
replies: text: The E and B fields have the same units relativistically speaking.  They only appear to have different units because a factor of 'c' has been taken out of the time unit and placed into the electric field unit.  Measuring time as a distance means qE and qB have units of momentum per meter.  Alternately, if distance is measured as a time, qE and qB have units of energy per meter (AKA force).  Alfred Centauri 18:35, 29 April 2007 (UTC)
replies: text: I still dislike how this is presented in the article.  Clearly the magnetic field and the electric field are inter-related, and it's reasonable to think of them as two aspects of the same thing, but I'd really like to see a source for the electric field being considered the more fundamental.  And if I don't see a specific source for the claim that Einstein said that "a magnetic field is the relativistic part of an electric field." I'm going to remove it from the article.    --Starwed 07:04, 30 April 2007 (UTC)
thread_title:  Relativity and the Magnetic Field 

message: Somebody put in a very novel but clumsy definition of the magnetic field as being an axis of all the possible directions that a force would act if a charged particle were to move perpendicularly to a magnetic field. 
Magnetic field lines are demonstrated to first day high school pupils by sprinkling iron filings on a sheet of paper over a bar magnet. When unlike poles are attracting, the magnetic field lines are acting like lines of force directly connecting the two unlike poles. That is about as basic a concept as we will ever get of a magnetic field line. It is a line of force. More precisely it is a line of tension.
You don't try to give an intuitive description of a line of force in terms of some specialized aspect of it, in this case the F = qvXB effect which is only one aspect of the magnetic field. That equation bears no relation to the force produced on a stationary charge by a changing magnetic field, or to paramagnetic attraction, or to diamagnetic repulsion, or to either ferromagnetic or electromagnetic attraction or repulsion.
Until such times as we agree on what a magnetic line of force actually is, then we will merely have to accept that it exists and describe it as it would be described to a high school physics student. (58.10.102.198 12:43, 1 May 2007 (UTC)
replies: text: Any comments on my proposed opening (previous section, in italics)? Notinasnaid 12:48, 1 May 2007 (UTC)

text: Thank you for your detailed reply. I see we are really debating something much more fundamental to Wikipedia, so I will start a new section, below. Notinasnaid 02:15, 2 May 2007 (UTC)
thread_title:  Introduction 

message: When I added the Wikipedia tag for "Too technical for a general audience" tag to the article, it led to a lot of very good discussion about definitions, which should continue. However, I feel it has largely avoided the real significance of this tag. At issue is not just whether the article is accurate (though this is vital), but whether it is accessible.
I'd recommend the linked Wikipedia:Make technical articles accessible in full, part of the Wikipedia Manual of Style, but I will also quote some of the key points. 
*"Articles in Wikipedia should be accessible to the widest possible audience. For most articles, this means accessible to a general audience."
*"Consider the types of readers that may encounter a technical article...The general public, with no technical background... it should be clearly established what field of study the concept belongs to, and if it has any practical applications. "
*"Put the most accessible parts of the article up front. It's perfectly fine for later sections to be highly technical, if necessary. Those who are not interested in details will simply stop reading at some point. "
*"Add a concrete example"
*"Use jargon and acronyms judiciously"
*"Use analogies"
*"Do not 'dumb-down' the article in order to make it more accessible. Accessibility is intended to be an improvement to the article for the benefit of the less-knowledgeable readers (who may be the largest audience), without reducing the value to more technical readers."
I contend that the article fails most of this test, except avoiding dumbing down, by any measure. At the moment it approaches the subject purely as an exercise in (largely theoretical) physics, except for a small and underdeveloped "applications" subsection of "See also", some mention of compass needles (though they are never put in context), and a good (but technical) discussion of electric motors in "Rotating magnetic fields". The article does not even use the word "electromagnet". 
I contend that to make this article accessible, it needs more material on applications, such as a complete subsection discussing applications in a non-technical way, probably first in the article after the lead sections (as this is likely to be the most accessible part). The technical aspects of these applications can later be referred to in context (as in the electric motors) section. 
Above all, the lead section needs to be rewritten. At the moment it is 
:In physics, a magnetic field is a force field that surrounds electric current circuits. A magnetic field can also be found in the vicinity of ferromagnetic materials such as iron. The existence of a magnetic field is ascertained by its effects. The most important of these effects are (1) Force on a moving electrically charged particle, (2) Force on a stationary charged particle when the magnetic field is changing, (3) Mutual force acting between two objects or electric current circuits that are surrounded by a magnetic field.
I realise technical details are under discussion, and this is more accessible to a "general technical audience" at about the level of first year college science course than it used to be. But words like "ferromagnetic" are an obstacle, and that's still about the simplest sentence. 
I contend that it is perfectly possible to write an article that the average child of age 10 or more can take away some enlightenment about magnetic fields from. Enlightenment such as "magnetic fields are what you get around magnets" and "magnetic fields make a compass work". Maybe younger; I don't know at what age magnets are introduced to a typical curriculum.
I have therefore proposed (elsewhere) a form of words which begins by defining a magnetic field in terms of the its most familiar everyday form, continues to list a handful of everyday applications (not an exhaustive list), and then moves on to provide a strictly accurate definition in terms of physics. Recall that the lead section should say nothing not repeated and expanded later in the article. I proposed earlier in this post that the first section following be an expanded applications discussion. Then the rest of the current article.
Before getting bogged down in a discussion of the form of words, I would like to open the debate on the general principle: How can we make this article more accessible? What do people think of the general framework proposed? Does anyone contend that the article would be fatally damaged by providing an opening that could be understood by a 10 year old? 
Comments please. Notinasnaid 02:58, 2 May 2007 (UTC)
replies: text: While I agree to some extent, the simple fact is that not all articles on Wikipedia can be accessible to a general audience, nor should they be.  However, this article should be, IMHO.  More technical articles related to this subject can be written and linked to from this article.  Do you agree or disagree with this approach, Notinasnaid?  Alfred Centauri 03:23, 2 May 2007 (UTC)
replies: text: I think the biggest problem with the article vis-a-vis a general audience has to do with Notinasnaid's point #3 (that is, with putting less technical things up front).  The first thing (after the intro) a reader sees is basically an equation.  Probably there should be a section or two on less technical or less mathematic material (similar perhaps to the Properties section half-way down the article).  I'm not saying take out the technical material (though a good rewrite seems in order), but move it to the end, after more discussing the magnetic field more generally.  And then, ease into it.  DAG 03:35, 2 May 2007 (UTC)

text: Good point.  Are you ready to start the editing?  Alfred Centauri 03:42, 2 May 2007 (UTC)
thread_title:  Too technical for a general audience 

message: Does all of the definition and mathematics in here apply purely to the magnetic field, or is any of it related to the electromagnetic field? Notinasnaid 19:34, 2 May 2007 (UTC)
thread_title:  A naive question 

message: I had to blink at this formula. The information is correct, I'm only nitpicking on the display. The formula is:
:F = I l \times B \,
Which is correct. However, directly after the forumla, the section goes on to label each variable within the formula with:
:F = forces, measured in newtons
:I = current in wire, measured in amperes
:B = magnetic field, measured in teslas
:\times = vector cross-product
:l = length of wire, measured in metres
This text (and this effect should replicate above) is in Arial. The capital I ("eye") and lowercase l ("el") appear exactly the same (pixel-perfect for me) in both IE and Firefox. The letters are also not in order, so some knowledge (which, hopefully, could be picked up in the article) is needed to decipher which variable is being explained.
Also, it seems a twee odd (and certainly doesn't help) that the variables are not labelled in the same order that they appear in the formula. They appear to be in no real order at all...
The text immediately below contains similar problems when discussing vectors with current and the segment. To clear it up, some possible solutions:
* Rearrange the variable explanations to match up with appearance in the formula.
* Could the formula be modified to use a capital L as opposed to a lowercase one? Anything wrong with this / would it be confused with other common uses? (such as L for rotational momentum?)
* Make the variable explanation monospace. This doesn't correct the paragraph afterwards discussing vectors, however.
* Is there an HTML entity for a cursive lowercase L?
I might "be bold" in a few days, but if anyone has any objections, now's the time to let the world know... ;-) (Ack, forgot to sign... these bots are fast!) Deathanatos 04:21, 3 May 2007 (UTC)
replies: text: Ah hah! There is a unicode script L, which might also help: It's ℓ and displays as ℓ. Kinda small... would it work? (It appears to be the character my physics equation sheet uses) Deathanatos 05:19, 3 May 2007 (UTC)
replies: text: But of course the HTML entity doesn't display in IE (at least for me in IE6)... I'm such a spoiled FireFox user... Deathanatos 05:21, 3 May 2007 (UTC)
thread_title:  Lorentz force on wire segment 

message: The force that acts on a moving charged particle in a magnetic field is a component aspect of electromagnetic induction. It was not incorrect to have mentioned it in the introduction. However it is a specialized aspect of the magnetic field and it has now been side referenced. An introduction to an article entitled Magnetic Field should only give an overview of the general picture of the magnetic field. The general picture is that of solenoidal field lines in conjunction with the fact that like poles repel and unlike poles attract. (201.53.10.180 16:20, 14 May 2007 (UTC)
thread_title:  Electromagnetic Induction 

message: I removed the section that claims that the magnetic field is an electric field as viewed by an observer in a moving reference frame. When I look at magnetic field lines around a bar magnet, I cannot imagine which rest frame I would need to be in in order for these field lines to become electric field lines. (81.158.161.160 20:26, 27 June 2007 (UTC)
replies: text:  Read any physics textbook - there is no magnetic field in the co-moving with charge frame (and don't forget that electrons have not only electric charge which creates electric field but also spin which is quantum mechanical motion - so electric field of electron is already in some motion). Moving electric field is what magnetic field is (to be more accurate - RELATIVISTIC component of moving electric field). Enormousdude 19:30, 28 June 2007 (UTC)
replies: text: If the supposed fact that a magnetic field is the relativistic component of an electric field is well documented in the physics literature, that doesn't mean that this fact needs to be added to the introductory paragraph in the magnetic field article. There have already been complaints that the article is too technical for the average reader. So why the insistence on adding this obscure and higly controversial piece of relativity into the introduction? (81.158.161.160 12:20, 28 June 2007 (UTC)
replies: text:  Hold on, the only reason magnetic field exists is special relativity (Loretz transformations). Not many people understand that (apparently including you, by the way). There is NO magnetic field in classic (Galilean) transformation of Coulomb force from co-moving with the source electric charge to non-moving reference frame of observer. None. Nada. Zero. So, if you remove it then a reader will be lost as to understand the origin of magnetic field. (Is this your intention - to promote personal ignorance to Wikipedia readers?) There are plenty of phenomena in nature which are difficult for "average reader" to understand because they require proper education of the reader. For instance, understanding of origin of conservation laws require knowledge of mathematical symmetries, of least action principle and of Emmy Noether theorem. So, should we simply state that conservation laws are just the way nature works, or should we point to their origin? If a Wikipedia project is to accurately explain things and phenomena (as encyclopedias suppose to do), then we should. Sincerely, Enormousdude 19:30, 28 June 2007 (UTC)

text: Um, sorry, no. Care to provide a reference for the idea that a magnetic field has nothing to do with Lorentz transformation, cuz I got plenty of sources that say otherwise. I think you're misunderstanding Maxwell's equations a bit; the vXB comes from the Lorentz force law. Maxwell's equations do a lot, but they say nothing about the force on charged particles due to those fields. However, prior to Einstein, the Lorentz force law was based only on observation. You cannot discuss magnetic fields without a discussion of how the magnetic force naturally comes out of the Lorentz transformation of the Coulomb force, with a vector field crossed into the velocity exactly identical to the magnetic field described by Maxwell's equations. Special relativity basically says why a magnetic field has to exist given an electric field. There is no force along the field lines, as ED has already explained above; the attraction between to bar magnets is due to a non-uniform magnetic field. If you're really interested, I highly recommend Jackson's "Introduction to Electrodynamics" for an exhaustive explanation of EM phenomena. Unless you've taken university courses in E/M then most of what you know of electromagnetism is likely a simplified analogy to avoid heavy math that leads to faulty understanding when taken too far. So either provide a reference for some of these claims (forces along magnetic field lines) or else this falls into the WP:OR especially when we can cite physics textbooks that state otherwise. --FyzixFighter 05:05, 29 June 2007 (UTC)
replies: text:  No reference is needed to show that a magnetic force exists along magnetic field lines. First form high school pupils learn that with iron filings. Look at the field lines joining two attracting magnets. The attractive force is along those lines. You are in denial of this most basic fact because you know that this aspect of magnetism definitely cannot be explained by the Lorentz transformation. (81.158.161.160 10:30, 29 June 2007 (UTC)
thread_title:  Origins of the Magnetic Field 

message: Sorry for the double post, but I just decided to be bold and changed the intro - the old intro was somewhat misleading and simplified to the point of absurdity (let's keep it "as simple as possible, but not more so"). It also already threw enough technical jargon around (axial vector, solenoidal) so the non-technical argument for not including SR in the intro doesn't hold water. I tried to model it after the the intro over at electric field. I think (or rather I hope) that I've avoided some of this "lines of force" disagreement by getting down to what the field describes, specifically in terms of the Lorentz force law. I also tried to address the "lines" question by using Faraday's original formulation (magnetic dipoles align themselves along these lines), since this is how most readers have been introduced to the concept, but leaving the more detailed explanation for later in the article. Also, certainly the full derivation of the magnetic field with SR does not belong in the intro, but it must be mentioned succinctly in the intro as this is a fundamental concept and is addressed later in the article. --FyzixFighter 06:42, 29 June 2007 (UTC)
thread_title:  Revision to intro 

message: I've found two web linked references that show that Maxwell had the Lorentz force long before Lorentz. First of all look at page 6 of the pdf file of this web link. It is Maxwell's original 1865 paper 'A Dynamical theory of the Electromagnetic Field'. Equation (D) on page 484 (page 6 of the pdf file) is the fourth of Maxwell's original eight equations. It is the Lorentz force. If we take its curl, we get Faraday's law. In the Heaviside versions of 1884, Faraday's law is preferred, but the vXB term has been dropped. Lorentz reintroduced it with his transformations. Here is the link,
http://www.zpenergy.com/downloads/Maxwell_1864_3.pdf
Also, I found another link which exposes this same fact. See,
* Waser, André, "Original Maxwell Equations"
(81.158.161.160 10:43, 29 June 2007 (UTC)
thread_title:  References 

message: Although this is a total sidetrack to the controversial issue in question, it does nevertheless make an interesting point for analysis. I dug up this google reference on the Lorentz transformation applied to the EM stress tensor. http://hepth.hanyang.ac.kr/~kst/lect/relativity/x850.htm
I realize now that it contains the Gauss force in addition to the (partial)dA/dt force. I would personally guess that it is the Gauss force that is involved in magnetic attraction.
At any rate, the vXB force purportedly unfolds following a Lorentz transformation on this tensor. Such would happen anyway simply by applying a Galilean transformation to the Heaviside version of Faraday's law, because all Heaviside did was to remove the convective vXB component that was already present in Maxwell's original equations. You have already seen it for yourself in Maxwell's original papers. The onus is still on you to explain how the vXB force could possibly act along B lines and account for magnetic attraction. I'm merely giving you the Gauss law as a hint. Think about it. Potential energy changes to kinetic energy. That does not happen with vXB. vXB by its very nature is not an attractive force. In fact I would venture to guess that vXB would act such as to precess a closed electric circuit, but not to attract it.(86.155.136.126 14:38, 2 July 2007 (UTC)
replies: text: You're misreading equation 6. Equation 6 shows how dA/dt gives rise to an induced electric field. Any force the results from dA/dt therefore is due to the induced electric field and is an electric force, not magnetic. This is an example of the continued point of departure between our interpretations of these equations. --FyzixFighter 17:22, 2 July 2007 (UTC)
thread_title:  Maxwell's Stress Tensor 

message: It might be good idea to start archiving this talk page beacuse it has become too long. --antiXt 22:15, 8 July 2007 (UTC)
replies: text: Archiving one discussion (under several headings) might be sufficient.  Gnixon 03:15, 11 July 2007 (UTC)
thread_title:  Archive 

message: Starwed and FizixFighter both mentioned a point which probably lies at the centre of the dispute. Both Starwed and FizixFighter mentioned that one should ignore the magnetic field of the object that is being acted upon. If we do that, then the F = qvXB effect can indeed be invoked, because the angles will be correct.
This method quite possibly gives a close approximation to the actual force in question but it overlooks the very important issue of potential energy. The forces of magnetic attraction and repulsion both involve an interplay of kinetic and potential energy which is not commensurate with the vXB force. Magnetic forces of attraction and repulsion are irrotational and they have traditionally been formulated by Gauss and Coulomb in the likeness of the electrostatic force.
It is clear to me now that modern textbooks have totally failed to interpret Maxwell and Faraday correctly. Maxwell and Faraday considered the exact picture of the magnetic field lines in any given scenario. Modern physics calculations are denying the correct picture of magnetic field lines crossing directly between two attracting magnets or spreading outwards between two repelling magnets. 
If the correct picture were to be employed, as opposed to the hypothetical idea that we should ignore the presence of the very object that is being effected by the force, then we would realize that we need a Coulomb force acting along the magnetic field lines to explain magnetic attraction. According to Maxwell, there will be a centrifugal pressure between the field lines that causes magnetic repulsion and that also pushes from behind a wire in magnetic attraction where the B line hooks around behind the wire. The vXB force quite simply doesn't work perfectly within the context of the actual picture of the magnetic field lines that exist between electric circuits and bar magnets.It is probably a good approximation for moving charged particles in a magnetic field. 
In summary, modern physics has ignored the potential energy issue, and it is using a distorted picture of how the magnetic field lines actually exist in a given scenario.
The vXB term is actually the convective aspect of -(partial)dA/dt under Galilean transformation. It first appeared in Maxwell's 1861 paper. We do not need relativity to explain magnetism. (217.44.98.235 18:52, 11 July 2007 (UTC)
replies: text: "It is clear to me now that modern textbooks have totally failed to interpret Maxwell and Faraday correctly."  Perhaps, but they are still considered reliable sources by Wikipedia.  This is not the place for original research.  Pfalstad 19:50, 11 July 2007 (UTC)

text: Are you referring to something in the article, or something on the talk page?  Only the article has to be sourced.  For physics articles, I think we need recent sources, not hundred-year-old ones, because Maxwell had some ideas which are discredited today.  Pfalstad 00:26, 12 July 2007 (UTC)

text: The 2006 research paper is not original research; it's in a reputable journal (Physica Scripta).  I'm not sure about the points you mentioned above, since I don't have time to wade through this entire talk page and figure out which points you are referring to, which IP addresses are yours and which are someone elses, etc.  Pfalstad 18:02, 12 July 2007 (UTC)
thread_title:  Magnetic Potential Energy 

message: To 83.131.82.23, I reverted your edits for the following reasons. The very reference that you supplied was none other than Einstein's famous 1905 paper in which the special theory of relativity first appeared.  
If you actually read Einstein's 1905 paper you will be in no doubt whatsoever that we need to have the full Maxwell-Hertz equations before we can apply the Lorentz transformation. Therefore you had no reason to delete that paragraph. The magnetic field is indeed pre-supposed before we apply the Lorentz transformation. And you can check out Maxwell's 1861 paper to see that vXB already exists independently of the Lorentz transformation.
The point which you are trying to press first came about in the late 1950's from a man called Rosser, but more famously in 1963 from Edmund Purcell.
If you think that your point is backed up by Einstein's 1905 paper, then let's please have the page number and line number. (217.44.98.235 09:24, 13 July 2007 (UTC)
replies: text: Can't you selectively revert instead of blindly reverting entire change(s)? No offense. --83.131.8.131 09:59, 13 July 2007 (UTC)
thread_title:  Application to Relativity 

message: The biggest problem I see with: 
:In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges, such as those in electric currents and bar magnets.
Is that I read it four times thinking that there are moving charges in electric currents and bar magnets, and I kept trying to remember where the charges move in the bar magnets. In other words, you have a misplaced metaphor. 199.125.109.127 05:05, 14 July 2007 (UTC)
replies: text: You are addressing that comment to FizixFighter. FizixFighter wrote that introduction. My wording was different. I only mentioned electric current and bar magnets in the introduction that I wrote. It was FizixFighter that insisted upon putting the emphasis on electric charge. I tried to keep it as electric current. FizixFigher kept reverting to moving single electrically charged particles. Eventually he compromised by allowing it to be mentioned that moving charges occur in electric current and bar magnets. (217.44.98.235 19:17, 14 July 2007 (UTC)
thread_title:  Intro 

message: I appreciate that wikipedia can not very well use the Hutchinson's introduction verbatim. But it is nevertheless a matter of interest to examine how mainstream encyclopaediae are balancing the complex issue of the magnetic field for a layman readership. Yesterday, I copied out the first part of the Hutchinson's article. See above.
As a matter of curiosity, I will now copy out the article in full as an illustration of how to word an article for the benefit of lay readership.
Magnetic Field. Physical field or region around a permanent magnet, or around a conductor carrying an electric current, in which a force acts on a moving charge or on a magnet placed in the field. The field can be represented by lines of force, which by convention link north and south poles and are parallel to the directions of a small compass needle placed on them.
It's magnitude and direction are given by the magnetic flux density, expressed in teslas.
Experiments have confirmed that homing pigeons and some other animals rely on their perception of the Earth's magnetic field for their sense of direction, and by 1979 it was suggested that humans to some extent share this sense. (217.44.98.235 16:27, 15 July 2007 (UTC)
thread_title:  More on the Hutchinson's Encyclopaedia Article 

message: Alfred Centauri, the fact that magnetic field lines are solenoidal means that div B = 0. It therefore follows that there must exist a vector A such that curl A = B. Maxwell used this vector A to derive the entire Lorentz Force. A is therefore the most fundamental of all physical quantities. It is the parent quantity for both vXB and the Coulomb force. If you would study the hydrodynamics of Maxwell's sea of molecular vortices it might help you to visualize the set up. (217.44.98.235 22:05,17 July 2007 (UTC))
:Anonymous, let's review your contradictory claims that you just repeated for all to see:
::(1) You said "Magnetic Vector Potential A is the most Fundamental of all Quantities"
::(2) You said "... magnetic field lines are solenoidal means that div B = 0. It therefore follows that there must exist a vector A..."
:(1) claims A exists period.  No need to rely on the existence and character of anything else.  That's what " most Fundamental of all Quantities" means.  If you believe "most Fundamental of all Quantities" means something else, then please explain to me what you think it means.
:(2) claims that A exists because B exists and is solenoidal.  But, if this is true, A cannot be the "most Fundamental of all Quantities"
:Anonymous, didn't you read my response to you regarding the example you gave to 'enlighten' me?  If not, I'll repeat it here:
::You said:  "However, I will leave you with something to think about. In hydrodynamics, curl v = Ω, where Ω equals vorticity and where v equals velocity field. Which is more fundamental? Vorticity or velocity? Likewise with A and B."
::I said:  "I will answer your question to me as follows: is it not true that in a region where Ω is zero, v may be non-zero? Is it not also true that in a region where v is zero, Ω must be zero? Then, would it be proper to say that vs existence is a consequence of the fact that vorticity field lines are solenoidal? I will leave you with that to think about."
:So, once again, how do you explain your contradictory statements?
No Alfred Centauri, A doesn't require the existence of B in order to exist. Velocity doesn't require the existence of vorticity in order for itself to exist.
However, when we know that vorticity does exist, we also know that velocity must exist.
From div B = 0, we can deduce that A must already exist.217.44.98.235 09:49, 18 July 2007 (UTC)
thread_title:  Magnetic Vector Potential '''A''' is the most Fundamental of all Quantities 

message: This is hard to read because every time B or H is referred to in the text, the math tag is used, making the letter huge.   —Preceding unsigned comment added by 71.112.193.232 (talk) 08:28, 29 February 2008 (UTC)
thread_title:  Article hard to read