Talk:Magnetic field/Archive 5

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In the diagram at "Force on moving charges and current" under "Magnetic field and electric currents" the drift should be along the electric field vector and the externally applied force vector.

Is new explanation in torque section ok?

I tried to include some more explanation in the torque section. If this helps people understand it then I will do the same in the force between magnets section. I am worried that this may be too much information, though. It is difficult to know what level to aim this article to. There is also the issue of brevity. Thoughts would be greatly appreciated. I have requested a more appropriate image to use for the torque on the magnetic dipole. TStein (talk) 20:32, 6 December 2011 (UTC)

Incorrect image

I deleted an image that portrayed the magnetic field getting stronger away from the source (a wire with current in it). RockMagnetist (talk) 15:15, 27 February 2012 (UTC)

Question about reality of field lines

Question:Could somebody please clarify if the field lines are an abstraction used to explain the concept, or if they are measurable. My understanding is that the field is continuous, and the lines are an abstraction used to show the direction. And that the field strength between two lines would be a simple distance-weighted average of the field strength at each line. Thanks — Preceding unsigned comment added by 98.247.120.111 (talk) 19:37, 2 December 2011 (UTC)

We tried to deal with this in the field line section. Essentially, field lines are mostly an abstraction used to explain the concept. They are also in a sense measurable in certain circumstances. (I have to be careful here the term 'measurable' like 'physical' or 'fundamental' mean different things to different people and can cause serious contention between editors without in my mind any real purpose.) Or maybe it is best to say that something similar to field lines that follow the same shape as a the abstraction we call field lines can be measured.

On example of this is sprinkling iron filings around a magnet. The magnetic field causes the filings to align in a very similar pattern to that expected by magnetic field lines. But since the magnetic filing are magnetic themselves, (the magnetic field much prefers to go through it than through air), the magnetic field with the filings will locally be significantly different than that without the filings.

Another example similar to this is that is when magnetic field interacts strongly with a plasma having little viscosity (like what happens on the surface of the sun). Here something very similar to the theoretical entity called field lines takes on a 'physical' form. These 'field lines' will have a definite tension and shear stress and will act in many ways like a stretched rubber band.

Sorry, if this isn't a very satisfactory answer; for being such a simple question answering it can be quite tricky. TStein (talk) 21:09, 2 December 2011 (UTC)

Look, there are no "lines." They are about as real as the topographic lines on a map, or the lines of longitude on your world globe. Choose to use different definitions of field strength and you'll get half as many lines, or twice as many, just as on a map. As for physical effects that seem to make lines visible, the line passing through the physical object is completely arbitrary, and the next time you put matter in the same field, would form someplace else (it's chaotic). You can drop iron filings on a magnet 100 times and get 100 different patterns, because they're not showing any linear "thing" that has any independent reality. The filings line up in a line, but they don't line up along any particular line. SBHarris 21:27, 2 December 2011 (UTC)

I think a better analogy would be with the flow lines of a fluid. Do you not think that flow lines exist? (I am ambivalent about whether or not they exist myself.) Regardless of whether or not you think that flow lines exist do you not think that one can measure them? What is real or not real is a matter for philosophers to debate. What is useful or not useful, or measurable or unmeasurable should be our concern. Topographic lines are measurable and useful as are fluid flow lines and magnetic field lines. It is important to note the caveats you mention, but we have to make certain that they don't swamp the fact that knowing the general shape of the magnetic field lines is often quite useful and that we can and do 'measure' them for that reason.

I apologize if I am rude, here. I agree with what you are saying, just not on all of the implications. TStein (talk) 22:32, 2 December 2011 (UTC)

I don't think flow lines exist in a fluid. Consider the gas in a wind-tunnel, a typical fluid. You can release smoke and see "lines" of it flow over a airplane model in the tunnel, but nobody really believes the smokey line is following some line-like thing in the flow. You can disabuse yourself of that by moving the smoke source a bit. It's apparent that the smoke lines in a wind tunnel are dependent on an arbitrary boundary condition, like a line that forms when you draw a paper under a fixed pen. Does the line that forms under the pen correspond to a "real" line in the flow of the paper? No! Movement of the flat paper in one direction there is, but lines in that movement, showing some kind of flow, there are not. We could even imagine the paper being stretched laterallly as it passed under the pen, and two lines made from two fixed pens would show that, as the lines converged and diverged. But again, the material has a elastic motion that can be graphed using the lines, but the lines are just graphs. We can extend this to nets of lines showing warped surfaces in differential geometry, but again, these things are no more real than coordinate axes. If you believe there are lines in fluids, do you think there are lines in space-time, when it is (say) warped by gravity in general relativity? I've certainly seen such lines in enough science shows! SBHarris 22:50, 2 December 2011 (UTC)

As a non-physicist I would ask "is there any difference between the field along the lines and between the lines?" If, as I suspect, the answer is "no, the field is uniform" then I would say that the lines don't exist. Richerman (talk) 13:09, 3 December 2011 (UTC)

Forget field lines. LINES don't exist in the real world! They're infinitely thin structures! ;-) Teapeat (talk) 15:19, 3 December 2011 (UTC)

On the other hand field lines, if done carefully, are useful in 2 dimensional magnetic field diagrams. In 3 D they're less useful because following a field line, due to the magnetic field patterns, usually gives an infinitely long chaotic pattern that never quite repeats(!)Teapeat (talk) 15:19, 3 December 2011 (UTC)

Any field theory can be graphed out using curved lines (sort of an oxymoron) or networks of lines. Magnetic fields are especially odd because they are relativistic effects of moving charges, so the loopy "line of magnetic force" (of course it's a closed loop) is just a graph of the various frame-velocities you would need to assume, at any point in space, in order to make the magnetic field at that point entirely disappear!

Similarly, in general relativity (another field theory), the network of curved lines sometimes shown to illustate the warping of space-time near a mass (with one spatial dimension left out) models gravitation by how much the network of lines are warped from being locally "flat" (cartesian rectilinear). The "slope" at that point is the gravity field. It also helps to model the velocity you need at any point to make the warping of space-time (gravitation) disappear for you, and your position appear "flat" (like you're standing on a point you can balance on). This curving path of such points is a geodesic calculated with a del.G at any point--it tells you the path you have to take (the inertial path of "free fall") to make all the lines at your exact position (locally) flat (rectilinear)-- even if they aren't flat at points very near you. Of course, if they aren't flat but sloped at your position, and you DON'T move (like standing on the ground here on Earth, which puts you on a slope in 4-space) you will feel a g-force a.k.a. proper acceleration and won't be weightless. And so on. Any field theory can be mapped in such ways, but the lines used to do it have no independent reality. They are GRAPHS conveying information graphically. The "lines" of magnetic fields curve like the economic output of Botswana! They aren't Euclidian straight lines, but (of course) curved lines. Is the GDP of Botswana "really, really, actually" a curved line? What? The idea is nuts. SBHarris 17:50, 3 December 2011 (UTC)

Careful Careful!! Nobody is claiming as to the validity of flow lines. What the concern is is about the existence and intensity of a force that exists and that is represented by the flow lines. And about a substantive entity that can extend and exercise that force. Note that the force disperses in intensity into a volume of space. Which implies that we are dealing with a volumetric situation here.WFPM (talk) 01:35, 17 February 2012 (UTC) SeeTalk:Newton's law of universal gravitation AndOrders of magnitude (magnetic field) I'll think about that "relativistic effect of moving charges" as a causative factor, but it would seem that something would have to exist to maintain and/or modulate the existence and dispersion of such a force. After all, we have to have either dynamic force entity or else a force intensity gradient to get anything done, unless you want to change the time increment value.WFPM (talk) 02:59, 17 February 2012 (UTC)

If you hang a cylindrical (neodymium) magnet on a string and let swing like a pendulum over a center location, and then place an opposing magnet at a fixed point under the low part of the swing, you will create an interaction of the two interacting fields such that the swinging magnet will bounce off of its path over the fixed magnet with an audible click and change in rotation direction; and which interacting motion will continue until the swinging magnet comes to rest at some distance from a position directly over the fixed magnet. So we obviously have 2 interacting magnetic fields with the capability of interchanging and storing up potential energy. How can we explain that without introducing some concept of matter that is capable of carrying out this process?WFPM (talk) 07:27, 13 October 2012 (UTC)

Also if you set up a target at the north pole of a permanent magnet and shoot some electrons at it you notice that they bounce off in a direction to the left. And it's hard not to imagine that they're bouncing off of an impact with something that is moving to the left. So we're wound up with a concept of a field of clockwise rotating forces within the field coming out from the north pole of the magnet, and which spread out as they get further away from the concentrating properties of the magnetic materials.WFPM (talk) 16:38, 17 October 2012 (UTC)

And what we need now is a concept of a some kind of matter that is capable of creating such a field.WFPM (talk) 16:32, 1 November 2012 (UTC)

Does any of this relate to improving the article? Remember that is the purpose of this talk page. RockMagnetist (talk) 16:43, 1 November 2012 (UTC)

Well it is to be noted that most scientific articles about things start out by a statement about what the subject matter is in reality. And then maybe its history of discovery and uses et cetera. Here we jump immediately to a set of mathematical formulea about some imaginary lines and without any discussion about what could be done to narrow down the discussion of the phenomenon to that of determining of the nature of its existence. And a lot of informative information exists, but it is not coordinated toward this goal. So where should this information go?WFPM (talk) 17:23, 2 November 2012 (UTC)

Are we looking at the same article? Magnetic field starts with a history section and has only one formula in the first three sections. Remember, too, that Wikipedia needs reliable sources. Do you have any that discuss the reality of field lines? RockMagnetist (talk) 17:28, 2 November 2012 (UTC)

I'd refer you to the article about the Luminiferous aether where a lot more effort is devoted to try to determine what the subject is, rather than what it does, and is therefore more informative. I guess it depends on what you're looking for in the way of information about a subject manner. And I'd really like to know how a mechanical force is propagated through a volume of space in which nothing exists.WFPM (talk) 18:12, 2 November 2012 (UTC)

That's a good question. The force is transmitted by virtual photons - something that should be discussed in quantum electrodynamics but isn't. I'll try to add something suitable. RockMagnetist (talk) 18:26, 2 November 2012 (UTC)

Well I appreciate your efforts and wish you lots of luck! But I think that the pendulum swinging trick over opposing magnets has convinced me that a volume of space must have some form of matter that can be caused to cohere sufficiently to allow physical forces to be propagated through it,WFPM (talk) 18:50, 2 November 2012 (UTC) And since this capability of force propagation also includes the force of gravitational attraction, (like the instance of the addition of the weight of a levitated object to the scale weight of the levitation apparatus), it must be of the same nature as that of the other natural forces of nature.WFPM (talk) 19:47, 4 November 2012 (UTC)

I don't know whether this will help for understanding. Choosing the right idiom might help. The idea of "lines of force" tends to confuse, because there are no separable lines per se, only a direction and magnitude of the distributed field. What is well-established from a classical perspective is the electromagnetic stress–energy tensor (I see there is also an article Maxwell stress tensor, which should be merged with it). There are well-defined stresses (pressure, shear etc.), momentum density and energy density in any electromagnetic field, just like in any solid or fluid. This article (Magnetic field) is curiously devoid of any mention of the stress. It may be useful, for example to outline that a magnetic field has a tension along the direction of the field and an equal pressure in the directions perpendicular to it, proportional to the square of the magnetic field strength. The energy density is also proportional to the square of the field strength. When there is no electric field, the momentum density is zero. — Quondum 04:50, 5 November 2012 (UTC)

Well if you agree it's like a solid or fluid, them what about maybe it is a solid or fluid? And how do you accomplish that in the absence of matter? It would appear that we haven't reached the lower limit of particle mass, like maybe that of a particle with a kinetic energy of planck's constant and a mass of 10E^-47 grams?WFPM (talk) 01:01, 6 November 2012 (UTC)

Don't get me wrong, but this is not the place to theorize about an unknown hypothetical composition of a field. And don't confuse "has a particular property just like" with "is like". We need to stick to what is known and established, and in this case the stress–energy properties of the magnetic field are the sum total of what we can say here about the forces within it. Please focus on changes needed in the article. — Quondum 05:13, 6 November 2012 (UTC)

I appreciate what you're saying and wish to note that I was only following along with the thought processes of the section about the reality of the magnetic field stress lines. Here you have a reality without an explanation. So? I have tried do introduce a few experimental facts, but I guess I can't draw any conclusions.WFPM (talk) 14:15, 6 November 2012 (UTC)

I've just made an update in an attempt to make the concepts a little clearer; feel welcome to comment on where this still leaves gaps for misinterpretation. Talking about hypothetical approaches can happen in user space (though I can tell you now that no interpretation involving a composition of "real" matter particles with any nonzero rest mass can be made to fit the math). — Quondum 16:14, 6 November 2012 (UTC)

Yes we have a problem when the mathematical description of something becomes dominant. I can imagine Edison's indignation when someone told him that in order to supply electrical energy to a customer it was not necessary for any material thing (electric current) to be supplied from his facility to the customer, but only a varying electromagnetic force which would cause the matter of his customer to become invigorated. Do you think we should just give up on understanding this phenomenon, or maybe try to consolidate the experimental data in an effort to better understand it?WFPM (talk) 17:42, 6 November 2012 (UTC) PS: I just finished reading the Georges-Louis Le Sage article and I can understand the problem.WFPM (talk) 02:59, 9 November 2012 (UTC)

And please note that it's one thing to explain an instantaneous and nonunderstood action by use of a virtual photon mechanism like a force carrying photon, but in the case of the static storage of a quantitative quantity of gravitational energy by the interaction of the 2 (gravitational and magnetic) force fields,(of the Pendulum versus magnetic field experiment) we have here a static energy storage experiment which requires the continued application of both of the involved forces. This is hard to explain without having the concept of some kind of system of matter that can support such a situation.WFPM (talk) 16:36, 13 November 2012 (UTC)

request for review of history section (will return favor)

I would like to request a thorough as possible review of the history section. (Like a mini-GA review if possible.) Does it have enough references? (It is probably too heavy on Whittaker for instance.) Does it have everything it should have? Does it have too much? Is it too long? What about images? The history section isn't consistent with referencing primary sources. De Magnete is referenced and linked but not Einstein's relativity paper. Should we include all important primary sources in the text, as a note, or remove completely? (I know that wikipedia discourages primary sources but I believe that history sections provide somewhat of an exception when combined with a good secondary source such as Whittaker.)

Thanks for any help you can give. I know that reviews are time consuming. Let me know if you want me to return the favor.TStein (talk) 18:58, 18 May 2012 (UTC)

Personally, I am finally satisfied with it having the right level of detail and completeness. I may merge the Poisson paragraph with the preceding one and simplify it. I would prefer that more primary sources were added such as historically important papers by Einstein, Lorentz, etc. And, I think it needs one more picture for balance. Maybe someday this article will be good enough for GA review. TStein (talk) 19:49, 23 May 2012 (UTC)

Math typesetting

This math typesetting on this page is currently done in a mix of straight HTML and Template:math. This makes for inconsistent display of math in the article, e.g.

the Lorentz force law is F = qv × B

versus

the Lorentz force law is F = qv × B.

We need to pick one or the other. I don't have strong feelings either way, although I'd probably go with straight HTML simply to save keystrokes. Does anyone have a strong preference for one or the other? Zueignung (talk) 21:23, 15 September 2012 (UTC)

This is, in my opinion, a Wikipedia-wide issue. Currently, I thought the MOS likes HTML in the text, but we know that it comes out different than the LaTeX, sometimes in a situation when little differences in style have mathematical meaning. Like in magnitudes of vectors: A = |A| vs. $A\ =\ |\mathbf {A} |\$. I think any decent text book would mix the exact rendition of the symbol in with the narrative text. Why don't we do that consistently here in Wikipedia math and science articles? Wouldn't a consistent standard be more encyclopedic? 71.169.186.150 (talk) 16:42, 14 December 2012 (UTC)

<math> Looks better, and a more familiar syntax (LaTeX) for those likely to be able to add competently to it. Offhand I don't see any use of either HTML or {{math}} in this article at present, it's all either wikitext or <math>. Andy Dingley (talk) 21:44, 15 September 2012 (UTC)

By "HTML" versus "Template:math" I mean the markup as explained here. The template {{math}} appears in the introduction and again in the section "Relation between H and B", among other places. Zueignung (talk) 21:50, 15 September 2012 (UTC)

My preference would be {{math}} because it looks more like the LaTeX equations, although it is tedious to implement. RockMagnetist (talk) 14:56, 17 September 2012 (UTC)

I've now made it consistent using {{math}} throughout (tedious it was indeed). Now, if need be, one can flip between {{math}} and {{nowrap}} easily by means of a global substitution. — Quondum 20:55, 17 September 2012 (UTC)

Good thought. Thanks for doing that! RockMagnetist (talk) 21:05, 17 September 2012 (UTC)

I think the current edit...

...this edit is correct. There are effects, but the magnetic field is really just the mathematical consequence of existing physics, the electrostatic interaction, when relativity is included in the consideration. 71.169.186.150 (talk) 16:29, 14 December 2012 (UTC)

You provided a diff. Do you mean the text after the edit? In quantum mechanics, magnetic spins also produce a magnetic field and are not a consequence of the electrostatic interaction. RockMagnetist (talk) 17:31, 14 December 2012 (UTC)

I strongly disagree with a school of thought (popular among people who are just taking freshmen physics, particularly with Purcell's textbook) to the effect of "God created electricity, and then electricity created magnetism". Electricity is not more fundamental than magnetism, the two are equally fundamental aspects of the universe. Electricity and magnetism are like siblings, not parent-and-child. Most people who have studied electromagnetism in more depth, like a course in QED, will agree.

BUT, I don't see anything objectionable in the edit linked above. I agree that TStein's text is just fine. --Steve (talk) 00:12, 15 December 2012 (UTC)

I agree with Steve, but this thread thusfar seems to ignore what I suspect was the motive for the edit: to say that A magnetic field is a region [of space]... was simply incorrect. — Quondum 06:05, 15 December 2012 (UTC)

magnetic fields,-Sub Structures.

The magnetic field as represented has its own internal anomalies; being if you noticed the field emitting from both ends exhibit individual lines as these lines are of the the same value and mAGNETIC CHARGE THEY FORCe THEMSELVES AWAY FROM EACH OTHER. for this to be acheived , they actually rotate in 3 dimensions, the timing differential being the time they are effected by the Time/Space value they are living in.This is their frequency over the surrounding frequency of interactions. Commonality to adhere to objects of and not of its internal structure is the dynamic action of lodging its telegraphed +/- to interact with the atomic structure make-up of a physical or positioned orbit object.In other words the time base movement of atoms is slightly distorted,allowing non complimentary (N/S) for simplification to attract each other The extension of this basic fact permits a cavalcade of hitherto unanswered questions about----- Regards Stephen Fitton- Australia. — Preceding unsigned comment added by 122.150.215.189 (talk) 20:21, 27 December 2012 (UTC)

Equation suggestions for electric and magnetic fields

The D-field and the H-field were defined as follows:

$\mathbf {D} \equiv \varepsilon _{0}\mathbf {E} +\mathbf {P} ,$

$\mathbf {H} \equiv {\frac {\mathbf {B} }{\mu _{0}}}-\mathbf {M} ,$

It doesn't take much of an eye to see their lack of correspondence.

My suggestions involve introducing a different symbol:
The symbol $\mathbf {I}$ represents the intensity of magnetization according to the Kennelly convention, Kennelly system of units, etc.

(https://www.google.com/search?q=%22intensity+of+magnetization%22+kennelly)

It equals the product of the permeability of free space $\mu _{0}$ and the magnetization $\mathbf {M}$. Notice that this is bold faced, unlike the symbol for current $I$, and also unlike the symbol for current density $\mathbf {J}$.

By introducing the symbol, we achieve a nice symmetrization of these equations for non-material conditions:

$\mathbf {E} \equiv {\frac {1}{\varepsilon _{0}}}(\mathbf {D} -\mathbf {P} )$

$\mathbf {H} \equiv {\frac {1}{\mu _{0}}}(\mathbf {B} -\mathbf {I} )$

The symmetry of these equations are apparent due to the following:

• LHS terms have units of volts/meter and amps/meter, respectively.
• The multipliers on the RHS have units of meters/farad and meters/henry, respectively.
• The terms in the parentheses on the RHS have units of coulombs/meter^2 and webers/meter^2, respectively.

Furthermore:

• The LHS term of both correspond to free charge and currents, respectively (i.e. not accounting for the material properties).
• The first RHS term of both correspond to free+bound charge and currents, respectively (i.e. accounting for the material properties).
• The second RHS term of both correspond to bound charge and currents, respectively (i.e. corresponding to material properties).

For material conditions, we have the following equations, which are also nicely symmetrized:

$\mathbf {D} \equiv \varepsilon _{0}\mathbf {E} +\mathbf {P}$

$\mathbf {B} \equiv \mu _{0}\mathbf {H} +\mathbf {I}$

Given the existence of relative permittivity > 1, it only makes sense that electric polarization complements E, in contrast to the standard assumption that electric polarization complements D. This means that D is the true electric field, in the sense that it accounts for the standard electric field as well as the polarization field, which is a separate entity.

Furthermore, we can note that:

$\nabla \cdot \mathbf {H} ={\frac {1}{\mu _{0}}}(\nabla \cdot \mathbf {B} -\nabla \cdot \mathbf {I} )$

$\nabla \cdot \mathbf {H} ={\frac {1}{\mu _{0}}}(-\nabla \cdot \mathbf {I} )=-\nabla \cdot \mathbf {M} ,{\text{(Because }}\nabla \cdot \mathbf {B} =0{\text{)}}$

$\nabla \cdot \mathbf {E} ={\frac {1}{\varepsilon _{0}}}(\nabla \cdot \mathbf {D} -\nabla \cdot \mathbf {P} )$

$\nabla \cdot \mathbf {E} ={\frac {1}{\varepsilon _{0}}}(\rho _{\text{f+b}}+\rho _{\text{b}})={\frac {\rho _{\text{f}}}{\varepsilon _{0}}}$

The effective charge density due to polarization $\rho _{\text{b}}$ is actually a deficit of charge density $-\nabla \cdot \mathbf {P}$. This is similar to the concepts of mass defect, which is not mass but a reduction of the mass, and binding energy, which is not energy held by a bond, but rather energy expelled by the bond.

E and H are a natural fit together because the Poynting vector (Abraham form) is:

$\mathbf {S} =\mathbf {E} \times \mathbf {H} ,{\text{(Temporal)}}$

D and B are a natural fit together because the Poynting vector (Minkowski form) is:

$\mathbf {S} =\mathbf {D} \times \mathbf {B} ,{\text{(Spatial)}}$

Other forms of the Poynting vector include:

$\mathbf {S} =\mathbf {E} \times \mathbf {B} ,{\text{(Electric monopole current)}}$

$\mathbf {S} =\mathbf {D} \times \mathbf {H} ,{\text{(Magnetic monopole current)}}$

Furthermore, as quoted in the article:

It is sometimes useful to model the force and torques between two magnets as due to magnetic poles repelling or attracting each other in the same manner as the Coulomb force between electric charges. In this model, a magnetic H-field is produced by magnetic charges that are 'smeared' around each pole. The H-field, therefore, is analogous to the electric field E, which starts at a positive electric charge and ends at a negative electric charge.

It is quite clear that:

• The ε₀E-field is what is left over from the D-field after subtracting the P-field.
• The μ₀H-field is what is left over from the B-field after subtracting the I-field (i.e. the μ₀M-field).

Interesting how the electromagnetic four-potential is based on (E,B) rather than (D,B). This likely means something. siNkarma86—Expert Sectioneer of Wikipedia
^{86 = 19+9+14 + karma = 19+9+14 + talk} 09:09, 11 April 2013 (UTC)

Every system has its advantages and disadvantages. I think the Kennelly system should be discussed, and the Sommerfeld system too; but making either of those the default would give them undue weight. As far as I know they are used far less than SI or even some of the cgs systems. RockMagnetist (talk) 17:44, 11 April 2013 (UTC)

Actually, since this is an article about the magnetic field, not the magnetization, these unit systems might have a more appropriate home at Magnetization, Maxwell's equations, International System of Units, or MKS system of units. RockMagnetist (talk) 17:52, 11 April 2013 (UTC)

Magnetic component of EM radiation

The article Electromagnetic radiation says nothing about the appropriate units for the magnetic component of EMR, while this article says nothing about EMR. Where can a Wikipedia reader go to learn about the appropriate SI unit for the magnetic component of EMR (teslas?), without the distraction in this article of trying to keep the distinction between B and H straight? Surely somewhere in Wikipedia there is the simple equation E = cB for EMR that would clear this up. Vaughan Pratt (talk) 23:20, 9 January 2014 (UTC)

There ought to be a discussion of units in Electromagnetic_radiation#Derivation_from_electromagnetic_theory and in Electromagnetic wave equation; you certainly shouldn't need to hunt as far afield as this article (where there is no reason that I can think of for a discussion of radiation). The electromagnetic radiation article claims that the relation E = cB "can be seen immediately from the Poynting vector" - the derivation is in Poynting_vector#In_plane_waves, and to me at least it isn't quite so immediate. RockMagnetist (talk) 23:42, 9 January 2014 (UTC)

Right, there it is, thanks. I was looking for it in the derivation, didn't think to look for it in the discussion paragraphs.

The bit about "can be seen immediately from the Poynting vector" makes no sense. First, the Poynting vector is derived from the assumption E = cB, second I don't see how one can get E/B = c from S = E × B --- there's a missing factor of B² there. Without an explanation I would think that bit should be deleted. Vaughan Pratt (talk) 03:35, 10 January 2014 (UTC)

On a second look, it appears that the Poynting vector is irrelevant - but the result is correct (I found it in a few different references). The key is that the wave is approximately planar in the far field, and then you need to use Maxwell's equations to derive the relationship. They haven't done that in any of the three pages. If I can find the time, I'll add it. RockMagnetist (talk) 06:19, 10 January 2014 (UTC)

The Earth and the planets

All popular theory to explain the magnetic field of a planet are wrong, because there is no known theory able to explain the obvious connection with the rotation, including why the direction of rotation and field approximately match. The rotation of the planet is obviously the cause of the magnetic field. Popular theory not even explain the polarity of the field. Despite the lack of evidence, outlandish theories about the magnetic pole reversals are common. In fact, the polarity is clear from the rotation and can therefore cannot change.

The correct explanation is actually surprisingly easy. The cause is simply the electric current generated directly by the rotation of the planets, and the charge separation of free ions by gravity. Positively charged ions are usually heavier than negative charged ions and are therefore shifted to the rotation axis.

We first consider only the negative charges, the electrons, of the Earth, neglecting the positive charges of the atomic nuclei. In 24 hours the total charge of the electrons crosses once through a cross section of the Earth. The mass of the Earth is at first approximation two times the mass of the protons, since there are about as many neutrons almost as heavy.

Then the current caused by the rotation of the electrons around the axis of the Earth within 24 hours is easy to calculate.

$\left({\frac {mass\,of\,Earth}{2\times mass\,of\,proton}}\right)\times \left({\frac {charge\,of\,electron}{24h}}\right)$ $=-3.3\times {10}^{27}\,A$

Since the Earth is electrically neutral overall, a current of exactly equal magnitude is produced by positive charges. The magnetic fields generated by both currents cancel each other almost completely. But, since the positively charged ions, however, are slightly shifted by gravity towards Earth's axis, the remaining effect of the negative charges causes Earth's magnetic field.

Franz Scheerer (Olbers) (talk) 17:47, 29 October 2013 (UTC)

This isn't the proper place for this; theories on how the Earth's magnetic field is generated should go in Dynamo theory, or Earth's magnetic field. However, if this is an unpublished theory, it doesn't belong in Wikipedia, which requires that all content be supported by published reliable sources. Maybe a better place for your idea is in Wikibooks? It doesn't require sources, and you could write a whole article about it. --Chetvorno^TALK 19:54, 29 October 2013 (UTC)

You're too kind. "Despite the lack of evidence" is outrageous given the extensive geological evidence for reversals. Moreover the proposed theory would predict a similar magnetic field for Venus and Mars, but Earth's magnetic field is more than a thousand times stronger than that of either of them. Vaughan Pratt (talk) 03:58, 10 January 2014 (UTC)

Ok, I again thought about it today. Indeed I'm convinced the reason for the magnetic field is as easy as I wrote some time ago. One may say, the (main) reason are free electric charges, namely ions in a liquid, and vertical charge separation due to gravity. The more heavy ions are seperated from the less heavy in direction to the rotation axis. Yes, it is so simple, the ions closer to the axis cause a field of lower magnitude. The direction of the field depends on weather the positive or the negative ions are more heavy. In gerneral, the more heavy ions are mainly positive metallic ions. Though in sea water the situation is different.

To explain the magnetic field of the planets my theory fits very well. Venus rotates very slowly and Mars has few liquid ions (too cold). 178.201.250.13 (talk) 10:15, 5 February 2014 (UTC)

Re: Recent changes to introduction

I just wanted to explain why I reverted your edits, Jwkeohane. The intro, and what should be said about B and H, has been the subject of an enormous amount of discussion on this page; see "Definition" above, as well as the archives. The current intro is the result of a consensus that the detailed definitions and history of B and H, and the question of which is the "true" magnetic field, should be deferred to the body of the article. All the introduction should say is that they are both vector fields which describe the magnetic field. Maybe we could discuss your proposed changes here. --Chetvorno^TALK 14:29, 17 February 2014 (UTC)

Chetvorno Thanks, but the prior version was totally misleading. I did think you were probably right about it needing to not dwell on the history so much, so I reverted them back, by moving the section to a footnote. It is important to realize that the introduction needs to be the best current physics definition, and not based on ideas that are 100 years old. (Jonathan Keohane (talk) 15:02, 17 February 2014 (UTC))

Your version is still misleading because it gives the impression that B and H are an anachronistic relic left over from a 19th century debate. You have to remember that the intro will be read by nontechnical people. It is confusing and unnecessary to go into the history of B and H in the intro. In modern terms, B and H are simply different mathematical models of the magnetic field, which are both equally useful. Also, your version does not make clear that B and H are vector fields, not just vectors.--Chetvorno^TALK

Actually they are not equally valid. What I have is correct. All notation in science is historical, but some is left-over from conceptually wrong physics like the pole model and the aether. But in this case it is particular egregious, because they measure the same thing in the lab. Thus, the only reason we still use H is because of pre-relativistic physics. This might be a good place to link to the history of the aether. Non-technical folks should not be confused by B and H, and realize that there is no need for H at all anymore. The more fundamental quantity is B, and H only exists for historical reasons. (Jonathan Keohane (talk) 19:00, 17 February 2014 (UTC))

It is also extremely misleading to general readers to say that "...magnetic fields and electric fields are one and the same..." That can promote the common misconception that the attraction of a magnet and a charged object are the same thing, the same field. The relation of electric and magnetic fields through Lorentz transformations should be left to the body of the article. The original version said much more clearly they are "two interrelated aspects" of the electromagnetic field tensor. --Chetvorno^TALK 15:54, 17 February 2014 (UTC)

You are technically right here, but mentioning tensors is way too advanced for the student wanting a quick, and correct, overview. So, my goal was to simplify the point, which is simply that depending on your reference frame, you will observed something as an electric or a magnetic field -- this is really a combination of the two. This is what induction is -- keep that in mind. Remember, Maxwell's equations are relativistic, and Einstein's brilliance was not to make some sort of Maxwell Stress Tensor, but rather to make the conceptual leap that Electrodynamics is more fundamental than Newtonian mechanics.

Your point about the misconception is totally correct! The thing to do is to figure out some nice way to make that point clear. Moving charged particles, do act like magnets, and magnets attract because of a gradient of the field -- so that is a hard concept. I think that someone, but probably not me, should write a nice early section on forces on magnets. (Jonathan Keohane (talk) 19:00, 17 February 2014 (UTC))

Does anybody else have an opinion about the new wording? --Chetvorno^TALK 19:29, 17 February 2014 (UTC)

I have not gone through everything in detail, but I don't think what we currently get taught at school should be considered anachronistic. In the macroscopic Maxwell's equations, it remains useful to distinguish B and H, and the lead should not sidestep the concept of a magnetic field inside matter. The historical confusion arises not from the fact that there is a misinterpretation or that there is really only one field, but is rather due to the dual use of the phrase to describe fields that have been given different definitions and units. In any event, no space should be given in the lead to the matter of confusion of terminology, other than to note that the term may have dual use. On the "one and the same", this is far worse than use of the word "tensor". Ideally, it should indicate that the magnetic field is an observational aspect of a single field, the electromagnetic field (which is a bivector field, not a vector field, but leave this for the body). —Quondum 21:26, 17 February 2014 (UTC)

My comments echo some of the above:

• The statement "it is a vector" is technically wrong: vectors and vector fields are not the same.
• The statement "Thus, physicists often refer to the magnetic field by their symbols B and H." makes no sense since the magnetic field is a single entity: B and H are vector fields to describe it.
• "B refers to magnetic flux density" is not necessarily common usage because B is also commonly called "the magnetic field" (some editors above support this). Consequently "The term magnetic field is somewhat confusing" is not really "confusing", it is a physical entity, the names for the vector fields B and H could be called a number of things (which is the confusion) which is clarified in the Definition section.
• The history section in the lead is irrelevant since the lead should say what the topic is, and not the development leading up to it, which could be what the subject is not! This is better suited to its own "history" section. Often, the historical development is not always the best way to present a subject because it can introduce misconceptions which were not understood in the past, but are now.
• "magnetic fields and electric fields are one and the same, depending on one's reference frame" is simply unclear, as said above.
• "They are produced by the charge" is also unclear and not true in general, again said above: a charge at rest relative to an observer will appear to produce an electric field and not a magnetic field - magnetic fields arise by relative motion between an observers and charges, for the purposes of a typical reader, the statement "moving charges" is probably enough.
• The mention of the electromagnetic tensor is important to mention in the lead after mentioning B (and H) because it is part of the extensively-used EM field tensor in theoretical physics (any application of special and general relativity, quantum field theory). There is no need to digress into details, this is just a pointer.

So I support the previous version of the lead. M∧Ŝc²ħεИ_τlk 23:15, 18 February 2014 (UTC)

That's three editors supporting the original version. Reverted changes. --Chetvorno^TALK 00:02, 19 February 2014 (UTC)

I too agree with the revert, and I would like to add that B and H do not measure the same thing in a magnetic material, the difference being the magnetization. Far from being a historic relic, H is used more than B in the theory of magnetic materials. The question of whether B or H is the "true" magnetic field is one of these pointless controversies that keeps resurfacing. Also, a version of the pole model is extremely useful in magnetostatics. It's only wrong if you interpret the poles as actual physical poles. RockMagnetist (talk) 00:39, 19 February 2014 (UTC)

I absolutely agree with RockMagnetist. Jonathan Keohane's statement above that there is no need for H anymore, and that it is only a leftover from pre-relativistic physics was completely mistaken (and the relation between B and H has nothing to do with relativity). If he expressed that point of view in an electromagnetics lab, he'd be laughed out of the room. --Chetvorno^TALK 01:21, 19 February 2014 (UTC)

I don't want to rehash a "pointless controversy", and I don't agree with Jonathan Keohane, but isn't there a significant truth he was trying to get at? The H model is not "useless" or a leftover as he claimed, but isn't it a less fundamental model than the Ampereic current B model? In the H model, the effects of magnetic materials are represented by a magnetization vector field M which is "smooth" on an atomic scale and just represents the "average" density of dipoles, so the H field can't represent the strong, locally varying magnetic fields between individual molecules, can it? If, instead, tiny circular "bound" currents j representing the individual dipoles (the electrons' spins) are included on the source side of Maxwell's equations, it will accurately give the B field on an atomic level. On an atomic scale, there is no H field, is there, only B? Or is that inaccurate? I'm not suggesting any changes to the article, I just want to understand; it's been a long time since I took electromagnetics. --Chetvorno^TALK 12:30, 19 February 2014 (UTC)

@Chetvorno: I'm afraid you're wrong on several counts. At an atomic scale, there are only point charges in a vacuum, so H and B are identical. If classical analogues are used, the magnetic field of the dipoles can be derived using microscopic currents, as you describe, or as the limit of two monopoles approaching each other. The physical models underlying these calculations are equally untrue. You're right that M comes out of a smoothing process, and therefore the difference between H and B. There may be a better argument for saying that the magnetic vector potential and magnetic scalar potential are the real fundamentals - consider the Aharonov–Bohm effect. RockMagnetist (talk) 17:12, 19 February 2014 (UTC)

I think that there are good philosophic reasons for distinguishing between B and H, even if they are related by a constant of proportionality. (I'll ignore the practical reasons, which are very persuasive.) These are essentially the same as the reason for the distinction between inertia and mass. When one fails to distinguish between concepts at this level, one has more difficulty framing questions properly. Merging B and H into the same concept also assumes that our theories are an exact description of physics, which we should never do (e.g. they'd presumably be distinct if the photon had a small rest mass, translating into a field that does not exactly fit the inverse square law). To be more explicit: H is defined in terms of the source charge and current distribution, whereas B is defined in terms of the force felt by a test charge. How the two are related is a matter of empirical observation, and of course descriptive theories. —Quondum 18:39, 19 February 2014 (UTC)

@Quondum: I'm not sure if you think I'm advocating a merger of B and H. Quite the opposite, actually. RockMagnetist (talk) 19:34, 19 February 2014 (UTC)

@RockMagnetist: No, I did not think that (I apologize if it seemed that I was responding to you; maybe I should not have indented). I actually have difficulty following your post since its referents are not clear to me, and couldn't quite work out what you were disagreeing with. I might disagree about the smoothing concept, since it seems that what is significant is what charge and current is classified as bound, not the small-scale structure. The "macroscopic" equations apply without modification to any scale ... until there is a movement from one classification to the other, e.g. in ionization. —Quondum 22:12, 19 February 2014 (UTC)

Hi Everyone, I think that you-all have convinced me that there needs to be a revision, simply because from a more practical point of view, rather than theoretical. But what everyone has to realize is that the previous version was both unclear and wrong, so yes we need something better than either my version or the one before.

First, the intro needs to give a clear definition of the magnetic field. And all the debate by people who know this stuff, but from different backgrounds, only underscores it. I teach physics, and am writing a textbook on this stuff, so I come from a pedagogical and historical point of view. The biggest problem student have is with the distinction between cause and effect, and we need to make that clear. So here are are few things we need to keep in mind:

1. B is defined based on the effects of a magnetic field. Thus, if one wants to measure a magnetic field, with an unknown source, the only kind of magnetic field one can measure is B. This was not understood in the 19th century, and the reason was that they assumed that the universe was filled with the aether, so it was assumed that we were inside a linear medium -- this was not true. (There is a nice wikipedia article on the history of aether theories.)

2. H is defined based on the cause of the magnetic field. Thus, if I have a wire with a known current running through it, I know, by definition, what H is due to it, even I have no clue about something else.

3. Magnetic materials are not linear, and even the most basic observations need quantum mechanics to explain. In the 19th century they thought they understood magnetic materials better than they really did -- the pole model worked quite well. They are difficult and need their own pages.

So, I hope we can all agree, that what the introduction needs is a clear definition of both B and H, in a way that can easily be measured in the lab. I think that we need to give in the introduction simply #1 and #2 above.

Who wants to give it a whack?

---

That said, I am right about H having no place in the physics curriculum, unless it is put in historical context.

until the students take solid state. On the other hand, I am not an engineer, but the introduction needs to be simple, clear and right.

But someone reading a book or paper with H needs someplace to go that defines it correctly with a good modern working definition.

Consider the following scenario in a lab:

My point is simply that what is actually measured in magnetic materials are two things:

1. The current and configuration of whatever is making the external magnetic field. By finding what the magnetic field would be, if it were not for the material involved, this makes a nice independent variable for the lab.
2. The magnetic moment per volume of the material involved. For example there are some nice experiments at NIST that measure the torque on a known volume of material in an external magnetic field. In these experiments, H is now the independent variable and M is the dependent variable.
3. And, of course, the magnetic field (B) outside of the material can also be measured.

B inside the material is inferred, so people really measure M but express it as B for historical reasons. (Jonathan Keohane (talk) 15:25, 21 February 2014 (UTC))

If you think H has no place outside a historical context, you are absolutely mistaken. You need to look at how B and H are used in modern engineering. Regardless, the introduction is not the place to address this issue. As a teacher, you should be able to appreciate the need to give an elementary grounding that general readers can understand, before getting into the more complicated stuff. --Chetvorno^TALK 17:02, 21 February 2014 (UTC)

I agree with Chetvorno. In my experience, when people start talking about putting better definitions in a lead, it's a sign of trouble. A period of hairsplitting follows and the result is tortured prose that tries to do everything in the first sentence. Meanwhile the body of the article is neglected. I think the lead is pretty good - most of the text is devoted to the significance of magnetic fields. RockMagnetist (talk) 17:13, 21 February 2014 (UTC)

@Jwkeohane: I would like to add that if you are getting your ideas about B and H from textbooks on electromagnetism, you should realize that they tend to do a bad job on magnetism (and by association, H). That includes classics like Jackson's Classical Electrodynamics. RockMagnetist (talk) 17:19, 21 February 2014 (UTC)

This is really a fundamental thing. H is defined from Ampere's law -- that is just all to it. It is a nice way to characterize what the magnetic field is due to another source. Now, of course, if you define H in terms of B and M, then you run into the problem I addressed before, H is not directly measurable, but it is very helpful when characterizing something in magnetostatics. But, as with any fictitious concept, it needs not be in the introduction. Actually I would agree that most textbooks are not fully clear, and that most people do not fully understand cause and effect in electromagnetism. First principles guys -- don't confuse people by implying that H inside a material is somehow real -- this debate was settled a hundred years ago. There are no magnetic monopoles. There is no aether. And, so the introduction needs to define these in clear and simple manner. — Preceding unsigned comment added by Jwkeohane (talk • contribs) 18:00, 21 February 2014 (UTC)

You're not going to get anywhere with nonsensical claims that H is not real. Look in any of the following books, the first two of which are classic works in ferromagnetism, and see which they mention first, B or H:

• Bozorth, Richard M. (2003). Ferromagnetism (Reissue of a [, ...] classic text. ed.). Hoboken, NJ: Wiley-Interscience. ISBN 978-0780310322.
• Jr, Sōshin Chikazumi ; English edition prepared with the assistance of C.D. Graham, (2009). Physics of ferromagnetism (2nd ed.). Oxford: Oxford University Press. ISBN 978-0199564811.{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
• Aharoni, Amikam (2000). Introduction to the theory of ferromagnetism (2. ed.). Oxford: Oxford University Press. ISBN 9780198508090.
• Spaldin, Nicola A. (2006). Magnetic materials : fundamentals and device applications (Repr. ed.). Cambridge: Cambridge Univ. Press. ISBN 978-0521016582.

I don't know what debate you imagine was settled a hundred years ago, but this is not it. RockMagnetist (talk) 18:17, 21 February 2014 (UTC)

Your addition of units to the lead was an improvement, though. RockMagnetist (talk) 18:39, 21 February 2014 (UTC)

magnetoquasistatic field, aka magnetic near field

This topic needs at least a link from here. Would it be better to just add it in the "See Also" section, or to add a small section in its own right, perhaps in the "Applications" section. I am thinking of something like this:

Magnetoquasistatic fields

Main article: Magnetoquasistatic field

A slowly-oscillating electromagnetic field in which the magnetic component dominates is called a magnetoquasistatic field or magnetic near field.

In resonant inductive coupling, a source and receiver are tuned to oscillate at the same frequency and are given similar impedances. This allows power as well as information to flow from the source to the receiver.

Applications include induction cooking, induction charging of batteries, Near-field communications (NFC), and position and orientation tracking.

— Cheers, Steelpillow (Talk) 09:43, 13 September 2014 (UTC)

It makes sense to me to have a section rather than a "See also" reference, since a static magnetic field and a magnetoquasistatic field are so closely related. To justify this intuition, I would include that magnetoquasistatic fields (as the name suggests) are in many ways approximated by static magnetic fields. I would also link to magnetic near field. —Quondum 15:47, 13 September 2014 (UTC)

Definition

Why is there no mentioning on how B relates to H? — Preceding unsigned comment added by 186.77.145.193 (talk) 02:09, 21 May 2013 (UTC)

The current definition is incorrect and confuses readers. The references are poor sources, and the information is not recognised by anyone I've worked with in magnetic research.

It would be better to remove the definition box with made-up alternatives, and leave the text as:

"There are two magnetic terms, H and B. In a vacuum they are indistinguishable, differing only by a multiplicative constant that depends on the physical units. Inside a material they are different (see H and B inside and outside of magnetic materials). The term magnetic field is historically reserved for H and magnetic flux density for B." — Preceding unsigned comment added by 84.92.38.86 (talk • contribs) 09:33, 12 May 2013

I don't have time to evaluate the situation (and it is a long time since I have thought about the subject), but I know that a lot of rubbish has been written on the topic, so you may well be correct. However, the text "There are two magnetic terms, H and B" is not quite right because a term is not magnetic. Not sure how to fix that at the moment, but I wanted to say thanks for the edit, and please add a space then four tilde characters to sign a comment on a talk page (see the links at your talk). Johnuniq (talk) 11:14, 12 May 2013 (UTC)

"Inside a material they are different" – this statement would have to be qualified, since it assumes the macroscopic definitions (see Maxwell's_equations#"Microscopic" versus "macroscopic"). They remain the same (up to a change in units) in the microscopic case), and this should not be ignored. Only the microscopic case can be made truly rigorous. Just saying: don't lose sight of the microscopic definition in this article. — Quondum 11:43, 12 May 2013 (UTC)

I reworded the paragraph a bit. It's somewhat confusing to say there are "two magnetic fields". Zueignung (talk) 07:07, 22 May 2013 (UTC)

I have made an edit in the definition panel, but I feel that the entire article should be revised in relation to my comments which follow. As a professional electrical engineer educated in the U of London, I am constantly perplexed by the conflation and confusion of B & H which I frequently see in discussions of magnetism which originate in the US, and by the almost universal practice there of refering to B as 'magnetic field'. In the SI (which is the only system of units I know anything about) B & H are clearly distinguished, and are in no sense the same. They have different units (Teslas, Amps/metre) and are dimensionally different; they are given distinguishing names - 'magnetic flux density' and 'magnetic field strength'. They are in fact different quantities related by this equation: B = u*H where u is the permeability of the material (or free space) in which the quanties are measured. u has units Henries/metre, and is not dimensionless. As well as being the proper name for H, the term 'magnetic field' is commonly used in layman's language to refer to a region of space, or of a material, which is magnetised. It seems to me that it is useful for a phycisist or engineer to use this latter, general, meaning of the term, but it is necessary to be careful to distinguish B from H by using the correct distinguishing terminology (flux density and field strength) when only one of these quantities is specifically intended. The present article is marred by an uncritical use of the phrase 'magnetic field' which, it seems, can refer indiscriminately to B or H or to an unquantified region of magnetisation . The article would be much improved if it were re-worded so that these concepts are properly distinguished. — Preceding unsigned comment added by G4oep (talk • contribs) 08:43, 31 August 2013 (UTC)

Have you read Section 2, "Definitions, units, and measurement", and note 4 yet? The uses of the phrase 'magnetic field' are clearly discussed and supported by citations. It is not the job of an encyclopedia to say that a widely used practice is incorrect. Note especially Purcell's comment that it is only the names that cause confusion, not the symbols. Meanwhile, I have never encountered your alternate definition of 'magnetic field' as a region of space that is magnetized; do you have references to support that usage? RockMagnetist (talk) 17:38, 31 August 2013 (UTC)

I have removed the dubious comment about space. If you have references to support it, I suggest adding the definition to the body of the article before changing the lead. Also, it seemed at best misleading in the second paragraph to specify that H is produced by moving charges, implying that B is not. RockMagnetist (talk) 17:47, 31 August 2013 (UTC)

I agree with RockMagnetist. Keep in mind, G4oep, that WP articles should be written as much as possible for a general readership, not just engineers. The introduction in particular is required to be comprehensible to ordinary readers. It seems reasonable to me for the introduction to simply say that the term "magnetic field" is used for both B and H, and defer to the body of the article the confusing explanation of why there are two vector fields, measured in different units, which both represent the same magnetic field. That is an accurate description of the usage: in scientific literature, when there is no possibility of confusion, either B or H is often loosely called the "magnetic field". But I agree that B and H could be better distinguished in the body text. --Chetvorno^TALK 20:46, 31 August 2013 (UTC)

I also support the reversion of the confusing language about "magnetized space" that was added to the introduction, but I sympathize with G4oep's intent. It's very difficult to write a definition of magnetic field for laypeople that also satisfies engineers. My personal opinion is the existing intro is pretty good, but could have a little more explanation (maybe one more sentence) for general readers. --Chetvorno^TALK 20:46, 31 August 2013 (UTC)

I feel that there is a difference in usage between British and US users of the concepts being discussed here, and I would like, if possible, to adjust what is written in the main article so that it makes sense to both. I feel that it would be a great advance in clarity, if ambiguity about the meaning of 'magnetic field' could be removed in the main article. If we agree to call B 'magnetic field' then what do we call H ? To me it seems unsatisfactory, and something that should be strenuously avoided, that the term should be used in scientific discourse with 2 distinct meanings. The meanings can be distinguished, and in fact are distinguished in the main article, but not consistently so. It is this inconsistency that I would like to see removed. I can only make sense of the idea that 'magnetic field' refers to both B and H by recourse to popular language, which has no need of the distinction. My Concise Oxford Dictionary (COD), Clarendon Press, Oxford, 1990, defines 'Magnetic field' as 'a region of variable force around magnets, magnetic materials, or current carrying conductors'. To my mind this 'region' (I previously mentioned 'space') could be in a vacuum or in some material, though the layman would probably expect it to be in air. I recognise this definition as the meaning used in lay speech, and it is to this that I referred previously; the COD is my reference for this. I would propose that this definition (or one like it) is put forward as a general, lay, definition of an unquantified magnetic field, but that 'magnetic field', and 'magnetic flux density' be used as terms to refer to H & B respectively as quantifiable concepts (vectors)in scientific discourse. B is not called 'magnetic field' in the UK; that term is reserved for either H or the layman's concept of the magnetic field, as given by the COD. I have been brought up with texbooks which give such definitions as "The vector H is known as the magnetic field", and "The vector B is referred to ... as the magnetic flux density " (both quotations from Electromagnetism for Electronic Engineers, R.G. Carter, Von Nostrand Rheinholt, 1986 - I am confident that other references could be found). Of course my comments are those of one who lives and works in the UK, and I am aware that others speak and write differently, but it seems to me that the usage I am proposing has the advantage of clarity and lack of ambiguity.— Preceding unsigned comment added by G4oep (talk • contribs) 09:06, 1 September 2013

Removing the ambiguity from the article will not remove the ambiguity from scientific discourse; it will simply make the article less helpful by pretending the ambiguity doesn't exist. I also doubt this is a UK vs. US/Canada/NZ/whatever issue. From a few minutes' poking around, it seems that David Tong's QFT lecture notes refer to B as "the magnetic field", as does The Quantum Theory of Light by Rodney Loudon (who was educated at Oxford, is now emeritus professor at Essex, and is so staunchly British that he insists on writing ∇. for the divergence instead of ∇·). If anything, I suspect this is a pure vs. applied science issue. The practice of referring to H as "the magnetic field" is something I usually see in texts on electromagnetics (i.e., electromagnetism applied to waveguides, antennas, etc.). Zueignung (talk) 18:38, 1 September 2013 (UTC)

If the COD defines magnetic field as a region, then it may be appropriate to give the definition a brief mention - but it is based on a misunderstanding of the mathematical concept of a field, and may just be a distraction. It would be interesting to see if the greater Oxford dictionary provides quotes for this usage. RockMagnetist (talk) 15:44, 2 September 2013 (UTC)

I looked at the Greater OED, and it was quite interesting. The relevant definition is definition 15a of FIELD, and there is a quote by Maxwell saying "The electric field is the portion of space in the neighborhood of electrified bodies, considered with reference to electric phenomena." It's hard to say what he means by that. The main dictionary definition is followed by this statement: "The concept of fields arose out of the work of Faraday and Maxwell. Fields came to be regarded as having an existence independent of the space they occupy." RockMagnetist (talk) 16:40, 2 September 2013 (UTC)

This reply is sidestepping the issue. There is no reason why the ambiguity cannot be removed from the language of the article, as long as the terminology and the fact of the ambiguity in "general" use is adequately addressed. There is no reason for the article to perpetuate the confusion; the editors are free to use unambiguous terminology (especially as such terminology does exist and is presumably standard pretty much everywhere except in the US) while making it clear to readers what terminology is generally in use and notable. It is not uncommon to say "in this article, xxx refers to yyy"; the editors can simply elect which terminology serves to convey the concepts with the least confusion, while clarifying what terminology is "usually seen", nor does it have to follow it (especially if this is WP:UNDUE). — Quondum 04:44, 2 September 2013 (UTC)

What specific usage in the article would you change? --Chetvorno^TALK 06:22, 2 September 2013 (UTC)

Is this acceptable ? In lay language, a magnetic field is ‘a region of variable force around magnets, magnetic materials, or current carrying conductors’ (COD as reference)'. This meaning is also used by members of the scientific community to refer to a general unquantified concept which can be differentiated into two distinct quantified mathematical descriptions of the magnetic influence of electric currents and magnetic materials. These are denoted by the symbols B and H. B refers to magnetic flux density, and H to magnetic field strength, but sometimes ‘magnetic field strength’ can refer to magnetic flux density (B). B and H are related by this equation: B = μH where μ is the permeability (reference needed) of the material (or free space) in which B and H are measured. B and H at any given point are specified by both a direction and a magnitude (or strength); as such they are vector fields.[nb 1] In the SI system, magnetic flux density is defined in terms of Faraday’s Law of electromagnetic induction (Wikki entry on Weber flux unit as reference). Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. The units of H are amperes/metre (A/m) which reflects this dependence of magnetic field strength on electric current. In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic tensor; the split of this tensor into electric and magnetic fields depends on the relative velocity of the observer and charge. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons.G4oep (talk) —Preceding undated comment added 07:44, 4 September 2013 (UTC)

This is for the introduction? --Chetvorno^TALK 21:48, 4 September 2013 (UTC)

Chetvorno - by 'introduction' do you mean 'lead'? RockMagnetist (talk) 23:55, 4 September 2013 (UTC)

Yes; I'm asking, is G4oep proposing this for the first paragraph of the article? If he is, my feeling is that the first sentence is a slight improvement on the current one, but the rest of it is too technical. The second sentence: "This meaning is also used by members of the scientific community to refer to a general unquantified concept which can be differentiated into two distinct quantified mathematical descriptions of the magnetic influence of electric currents and magnetic materials." is way to stuffy and wordy. It won't resolve any "ambiguity" or "confusion" about the term magnetic field, because most readers will give up long before they reach the end of the sentence. The lead should introduce B and H and give their units and most common names (flux density and field strength), but it doesn't need to give alternate names. I don't think the equation B = μH needs to be in the intro. In sum, I like the intro better as it is, except for adding the units of B and H. --Chetvorno^TALK 02:58, 5 September 2013 (UTC)

I am still skeptical that "magnetic flux density" is the most common name for B, at least in pure physics. In my experience, B is referred to predominantly as the "magnetic field". This is the case with Purcell's and Griffiths's E&M books (though notably not Jackson's) as well as Sakurai's Modern Quantum Mechanics. Purcell and Griffiths both go out of their way to mention that B is, in practice, not usually referred to as the "magnetic flux density", but rather as the "magnetic field". Zueignung (talk) 05:02, 5 September 2013 (UTC)

Even Jackson starts by calling B the magnetic field, then on the following page introduces H and says "The two new field quantities E and H, usually called the electric displacement and magnetic field (B is then called the magnetic induction) ..." RockMagnetist (talk) 16:16, 5 September 2013 (UTC)

Then what do we call H? It's most often called "magnetic field strength". I don't really care what they are called - as Purcell said the only confusion is with the names; the mathematics is perfectly clear. We have a good table in the article giving the different terms used for B and H. --Chetvorno^TALK 10:43, 5 September 2013 (UTC)

I usually hear it called "H" or the "H-field". This more or less follows what Griffiths has to say about it, which is that "H has no sensible name: just call it 'H‍' ". "Magnetic field strength" sounds like you're talking about the absolute value |B| (as in, "the atoms are subjected to a strong magnetic field"). In Purcell's chapter on magnetism in matter, he refers to everything as much as possible as "the B-field" or "the H-field", which I think is probably the right way to go for the bulk of this article, simply so that readers are not constantly doing double-takes at unfamiliar or jarring nomenclature. Zueignung (talk) 14:07, 5 September 2013 (UTC)

I agree with Zueignung that the terms "B-field" and "H-field" would be simpler to use, since there's no ambiguity in terminology, there is a direct reference to which vector fields are used, and they're easier to write. As Chetvorno says, there is already a clear table for alternative names, and the lead should have the common names anyway. M∧Ŝc²ħεИ_τlk 14:27, 5 September 2013 (UTC)

Yes, I agree, that would be clearer. --Chetvorno^TALK 14:37, 5 September 2013 (UTC)

How do other people feel about the issue G4oep raised, the language in the introduction that refers to both B and H as the "magnetic field"? --Chetvorno^TALK 14:54, 5 September 2013 (UTC)

I think that any definition of the magnetic field as a region should be avoided, even when talking about lay language. As I described above, the support for this definition in the OED is very weak, and scientists always draw a distinction between fields and the space they permeate. I also think that extensive discussions of nomenclature should be avoided in the lead, because its purpose is to summarize the whole article. RockMagnetist (talk) 16:24, 5 September 2013 (UTC)

I agree with RockMagnetist on the specific points mentioned. Description as a "region" is archaic and the COD/OED should not be considered a reliable source on matters of a scientific nature, even from a lay perspective. From a modern perspective it is simply an incorrect description: a field might occur in a region (along with other fields), but it is not that region. Would you describe a person as a region in space? The textbooks that I learned from at school level took pains to specify distinct terms for H and B. The terminology issue cannot be sidestepped in the article, but it can be minimized in the lead. The reason is that this article will be sought out by students precisely to resolve issues of terminology. This suggests that we should devote a section to discussion the confusion of the terminology (in addition to the existing table of alternatives), and to state the naming policy adopted in remainder of the article. Then we should use something unambiguous for the remainder for the body of the article, e.g. B-field and H-field as Maschen says. I don't like the lack of uniform established terminology, but using one of several meanings of the same term would be POV. I suggest that we never use the term "magnetic field" when specifically one of the fields is meant, but when the ambiguity is irrelevant, it is fine. — Quondum 21:45, 5 September 2013 (UTC)

There already is a section (2.1) for discussions of the terminology. RockMagnetist (talk) 23:55, 5 September 2013 (UTC)

I disagree. We should not conflate use of terminology with definition of the concepts. It should be split out into a separate (sub?)section. — Quondum 02:26, 6 September 2013 (UTC)

There is an incoherent conflation in the definition used in the introduction. The first sentence says "A magnetic field is a mathematical description..." Then the second paragraph says "Magnetic fields are produced by moving electric charges..." If these were both true statements then one could combine them and say "A magnetic field is a mathematical description produced by moving electric charges." But this is an incoherent conflation because electric charges are concrete physical objects and descriptions are abstract mathematical ideas. If a magnetic field is a mathematical description then it is a description produced by human minds, not by electrons. I agree that fields in physics are abstract mathematical descriptions of some concrete physical thing that exists in space. In the case of a wind vector field, the field is a description, and the things being described are moving gas molecules within a defined area. The described things and the description itself should not be and cannot coherently be conflated. So can we say that a magnetic field is a description of moving electrons within a defined area? — gcsnelgar 20:50, 20 April 2014

No, a magnetic field is the vector force field generated by the moving charges, that is the intent of the phrase "mathematical description". The essence of the idea is that it is a condition of space that is viewed as separate from what generated it. For example, when you look at a star, your eye is responding to oscillating electric and magnetic fields emitted by an electron in the star, perhaps thousands of years ago. The electron which created the magnetic field could have been annihilated by another particle long ago, or the star could have collapsed into a black hole. It would be pretty silly to have to refer back to the hypothetical motion of an electron thousands of years ago to define the magnetic effects. Instead the light wave is described in terms of an oscillation in the electric and magnetic field, travelling through space. --Chetvorno^TALK 22:07, 20 April 2014 (UTC)

While I disagree with the idea that the field is the description, a good point is being made. In effect, the language of the first sentence is wrong. —Quondum 22:11, 20 April 2014 (UTC)

I think the previous sentence was adequately comprehensible. The lead sentence now is pretty much a circular definition that gives little information: "A magnetic field is the magnetic influence." --Chetvorno^TALK 22:53, 20 April 2014 (UTC)

It would be very good if this issue could be resolved, as well as can be, the text suitably fixed to most people's liking, and, then, finally, we indicate that all of this has been done! Still ticking, Grandma (talk) 15:20, 24 November 2014 (UTC)

Incorrect diagram?

In the diagram at "Force on moving charges and current" under "Magnetic field and electric currents" the magnetic field should be going into the page, with a cross instead of a dot, for it to be correct, unless I'm going totally insane --92.28.205.1 (talk) 22:50, 19 April 2016 (UTC)

Charged particle drifts in a magnetic field with (A) no net force, (B) an electric field, E, (C) a charge independent force, F (e.g. gravity), and (D) an inhomogeneous magnetic field, grad H.

Do you mean this diagram? If so, then it is correct. Look at the cross product in the Lorentz force law

$\mathbf {F} =q\mathbf {v} \times \mathbf {B}$

For a positive charge (q > 0), v is tangential to the circle, B upwards out of diagram, so which way is the force? Perpendicular to v and B directed "right" in the plane of the diagram, towards the centre of a clockwise circular path. For a negative charge the direction of force is reversed ("left" in plane of diagram, anticlockwise path). Hope this helps, M∧Ŝc²ħεИ_τlk 23:03, 19 April 2016 (UTC)

Sorry, it's the directions of the Larmor orbits that need to be switched. By the right hand grip rule, the current will be anticlockwise, so the positive charge should orbit anticlockwise and the negative charge should orbit clockwise 31.205.113.23 (talk) 10:29, 13 May 2016 (UTC)

Fleming's left-hand rule for motors is for conventional current (current sense along flow of positive charge). The right hand rule for negative charges. M∧Ŝc²ħεИ_τlk 11:20, 13 May 2016 (UTC)

It's the deflection of a charge moving through an external magnetic field.

It's not the magnetic field generated by a charge moving in that path.

It goes the other way. So the picture is correct.

^talk2siNkarma86—Expert Sectioneer of Wikipedia 02:37, 15 May 2016 (UTC)

So it turns out I confused the right hand grip rule for solenoids with the motion of a free charge in a magnetic field. So yes, the diagram is correct. --31.205.113.23 (talk) 08:23, 15 May 2016 (UTC)

Rationalization and simplification needed

This article, although it contains a wealth of information, starts off at the deep end and gets deeper and I am afraid to say will be no help whatsoever to the average reader trying to get an understanding of what a magnetic field is. CPES (talk) 19:57, 17 December 2016 (UTC)

There is a missing character, the Greek letter phi meant to represent flux is not showing.

Units[edit source]

The 'phi' standing for magnetic flux is not displaying. The missing 'phi' is a problem in many pages, not confined to this page.

Further down the page in the discussion of magnetic torque on a magnet in a field, the Greek letter tau is not displaying.

The problem I describe seems to be browser dependent. The OPERA browser does not support the font apparently, but the CHROME browser and Firefox do. RDXelectric (talk) 08:37, 5 November 2016 (UTC)

Just wondering - do you see Φ here? RockMagnetist(talk) 22:32, 17 December 2016 (UTC)

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International System of units for the field B

The B field units in the SI are described as Tesla = newtons per meter per ampere [...] in the SI. However, Newtons are a derived unit not a base unit from the SI. Wouldn't it be better if we defined the Tesla from basic units? This would give : Tesla = (kg*m^2) /(A*s^2) Leonel Gouveia (talk) 12:49, 1 June 2017 (UTC)Leonel D. Gouveia Ergin

wrong or whatever

a field is defined as force over quantity. in magnetism, the quantity is the flux, φ so H = F/φ = (Fd/φ)/d = (W/φ)/d while W/φ is magnetic potential / magnetomotive force measured in Amperes, so H (A/m). the density is quantity per area, so B = φ/A = (φ/t)t/A. the φ/t is electromotive force measured in Volts, so B (V.sec/m2). step back in electricity the quantity is charge, q so E = F/q = (Fd/q)/d = (W/q)/d, the W/q is electric potential, u. so E (V/m). the density is D = q/A = (q/t)t/A = it/A so D (A.sec/m2). in gravity the quantity is mass, m so G = F/m = (Fd/m)/d = (W/m)/d, W/m is gravitic potential, h that can be measured in Grays, so G (Gy/m). the density: J = m/A = (m/t)t/A = yt/A while y is gravitic current measured in cail/sec (Le[gendre]? ). also we can define gravitic flux, β (that is in rhyme with φ, compare: φ/t = u, β/t = h). for field we have C = F/β = (Fd/β)/d = (W/β)/d. the W/β is mechano-motive force, y so C (Le/m). it's weird but C field is exactly the dynamic viscosity and dimensionally equivalent to Pa[scal].sec, for density: K = β/A = (β/t)t/A = ht/A so K (Gy.sec/m2). the Newton law can be shown as F = mvK so K is in bond with a = vK (i.e. we can define acceleration as vK, not v/t). compare: F = qvB = φvD = βvJ (see? B is in density row. field row: u = Ed, i = Hd, h = Gd, y = Cd). for units mentioned, Gy and Le, the torque, τ and angular momentum, L can be easily measured in Gy.cail and Le.m2, while angular velocity, ω and acceleration α, shown in Le/cail and Gy/m2 respectively. (cail, c, is chilog[ram] ) {I say, we can result equivalency principle: the m in F = mvK is that in F = k_G.m₀m/r2 if the q in F = qvB is that of in F = k_Eq₀q/r2, (and for two magnets: F = φvD and F = k_Mφ₀φ/r2) (and hydrodynamics? : F = βvJ with F = k_Zβ₀β/r2) .
Tabascofernandez (talk) 23:28, 14 July 2017 (UTC)

Why it is conservative ? Bibhabasu Mondal (talk) 06:49, 10 April 2018 (UTC)

Possibly a mistake

I believe there is a mistake in the sentence reading: "Then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction repel one another.". It should say "attract each other" (alternatively, "wires having currents in opposite directions repel each other"). Can someone please check this? — Preceding unsigned comment added by 152.170.204.11 (talk) 22:53, 23 March 2018 (UTC)

Thanks for pointing this out. Someone had already corrected it; I expanded the statement to cover both cases and added a citation. RockMagnetist(talk) 16:54, 10 April 2018 (UTC)

H-field

The H-field is not defined. Phrases like "there is a quantity H, which is also sometimes called the magnetic field" do not make up for a definition. — Preceding unsigned comment added by 5.55.156.124 (talk) 06:39, 5 February 2018 (UTC)

The H-field is defined; it is just not done so in an obvious location. Part of the problem is that the definition of the H field involves first defining what M is. Does anyone here have any brilliant ideas of how we can do that better? How do we make the definition of H more prominent and earlier without burdening the article too much with technical details about M? TStein (talk) 23:02, 18 April 2018 (UTC)

A historical query

The History section seems to imply the Thomson had worked out a clear understanding of H and B by 1850. But I have the impression that there was uncertainty about whether H and B were physically different, and this was not resolved until around 1930 ([| History of IEC]). Or have I misunderstood something? Sdc870 (talk) 03:51, 20 April 2018 (UTC)

Interesting link. I wish I had more time to study it in detail. It is not unusual for there being a lag from when an idea was first proposed and shown to be true to when it is generally accepted. I have no clue if that is what happened here, though. I also find it strange that a committee would have the power to formally decide if B and H were two different quantities or not. If so it would seem historic to me. It might be worth you adding a sentence to the history section about this. TStein (talk) 15:49, 20 April 2018 (UTC)

@TStein: More than a "committee". IEC members are national representatives, usually with connections to the national laboratories responsible for standards and measurement. Perhaps better analogy is to "climate change" and establishment of a scientific consensus. (To others: I should have quoted the relevant sentence from the IEC link: "The much discussed question of the difference between the nature of the quantities H, magnetic field strength, and B, magnetic flux density, was finally settled.") — Preceding unsigned comment added by Sdc870 (talk • contribs) 10:20, 21 April 2018 (UTC)

Discussion of units for B and H in lead is too heavy

Suggestion no. 2 The details and complication in the discussion of B and H and units of measurement seem too heavy for a lead section. Can the issues be stated in a more abstract form? For example (in the direction of): There are different magnetic fields (usually denoted with B and H), and measured with different units. (As I understand, the lead section is just informing what the article is about, and where the "links" in the Contents can be used to get into the details.) Sdc870 (talk) 04:40, 20 April 2018 (UTC)

I personally don't think that paragraph is too heavy. If you decide to fix it remember that one of the most asked for things on this talk page is the exact relation between B and H. I could support deleting the line that spells out the units as being to esoteric for the lead (others will disagree). I could also support changing the sentence relating B and H to the equation it describes. As a general rule equations feel a little less heavy when written symbolically out then when described in plain english. Non-technical readers may disagree, but I don't think that you will get very far in any article about magnetic fields without some comfort with equations. TStein (talk) 15:35, 20 April 2018 (UTC)

p.s. Sdc870 wrote the comment before I made the section to make it easier to find. (I hope this does not break etiquette or cause confusion.) TStein (talk) 15:35, 20 April 2018 (UTC)

@TStein: I have changed the title of this topic to better reflect that my suggestion was limited only to whether the units and their definitions should be named explicitly in the lead, given that they can be easily found in the article. My suggestion was aimed at finding a happy medium -- maybe mentioned units, but not all the technical details. Sdc870 (talk) 11:22, 21 April 2018 (UTC)

@Sdc870: I also don't think the discussion of B and H in the intro is too "heavy"; in my opinion the current wording is close to the minimum that is consistent with the requirement that the lead be an "adequate summary" of the article (WP:LEAD). I feel the units of B and H have to be included in the intro because that is a common piece of info that students and general readers come to this page for, and units are given in the lead of virtually every other scientific quantity on WP. In fact, I think that the widely used alternate units webers and gauss need to be added. --Chetvorno^TALK 19:30, 20 April 2018 (UTC)

@Chetvorno: My point was only about naming the units. Clearly a matter of taste. Perhaps not so useful for the non-technical reader. If kept, maybe that paragraph should be moved to the end of the lead section -- especially if alternative units are also added. Sdc870 (talk) 11:22, 21 April 2018 (UTC)

@Sdc870: By the way, I think most sources would not characterize B and H as "different magnetic fields". They are separate vector fields that provide alternate representations of a single magnetic field. --Chetvorno^TALK 19:30, 20 April 2018 (UTC)

@Chetvorno: Seems like an important point to correct! Should the first sentence in the second para. be something like: "The magnetic field is described by two vector fields, denoted by the symbols B and H." Sdc870 (talk) 11:22, 21 April 2018 (UTC)

@TStein: I agree that the English description of the equation in the intro 2nd para is a little clunky, I wouldn't mind it being replaced with some more general statement. However I think it's less scary for general readers than an actual equation. The late Stephen Hawking included only one equation in A Brief History of Time because he was told that every additional equation he added would cut readership by half. --Chetvorno^TALK 19:30, 20 April 2018 (UTC)

Needs to be more accessible

The subject of the "Magnetic Field" is complicated and involves a great deal of upper level math. Lots and lots of awe inspiring differential equations and integrals. In the opening "survey" paragraph of this Wikipedia article (in fact, any Wikipedia article) the discussion should be simple enough that an interested and motivated high school student can read it and come away with a decent mind's picture of what a magnetic field is. What causes one, and what it can do regarding force. The present opening paragraph doesn't do this. What good does it do for a physicist to write an article that only a physicist can, and probably already does, understand? J Devore, Philadelphia — Preceding unsigned comment added by 73.81.157.156 (talk) 21:07, 5 November 2017 (UTC)

I partly agree. This topic is just intrinsically complicated (more so than Electric field) so the introduction is unavoidably going to refer to some esoteric stuff, but as you say the introduction is supposed to be understandable by general readers, and I think it could be improved. The lead sentence:

"A magnetic field is the magnetic effect of electric currents and magnetic materials."

has always bothered me, it seems too vague. How about something like:

"A magnetic field is a force field that is created by moving electric charges (electric currents) and magnetic dipoles, and exerts a force on other nearby moving charges and magnetic dipoles."?

--Chetvorno^TALK 22:38, 6 November 2017 (UTC)

As another non-physicist I also agree. Those suggestions sound like an improvement to me but the real killer is the sentence that reads "The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter (symbol: A⋅m−1 or A/m) in the SI. B is measured in teslas (symbol: T) and newtons per meter per ampere (symbol: N⋅m−1⋅A−1 or N/(m⋅A)) in the SI." That is far too long and complicated for a single sentence and do we really need all that detail in the lead anyway? At a minimum I think we should lose all the parts in parentheses about symbols and confine those to the body of the article. Richerman (talk) 23:24, 6 November 2017 (UTC)"

Hmm, in fact I've just realised it's two sentences but they are so complcated it's hard to tease them apart. How about simplifying this to "The term is used for two distinct but closely related fields denoted by the symbols B and H, where, in the International System of Units, H is measured in units of amperes per meter and B is measured in teslas or newtons per meter per ampere". Richerman (talk) 23:56, 6 November 2017 (UTC)

Just for background, this sentence was the result of a Talk page discussion a few years ago that concluded that (1) B and H need to be mentioned in the introduction since they are the vectors representing the magnetic field and a lot of the article revolves around them, but (2) the intro shouldn't try to explain the difference between them, but just give the units they are measured in. Since this article is about a physical quantity, I feel the units need to be given in the intro, although maybe not in as complicated a form as the current sentence. Richerman's new version is better; it would be fine with me. --Chetvorno^TALK 00:37, 7 November 2017 (UTC)

I think the rewording proposed by Chetvorno and Richerman are both improvements, but a little more needs to be said about the relationship between B and H. At this point, it seems easiest to just try rewriting the first paragraph, so I have done that. I removed the note about a magnetic field being a pseudovector because I think it is too technical for the lead. The point is made in the body of the article. RockMagnetist(talk) 17:39, 7 November 2017 (UTC)

RockMagnetist's version looks good to me; if the intro is to include math, these are the minimum equations that should be included. --Chetvorno^TALK 18:03, 7 November 2017 (UTC)

Ah but, that's my main point - should we have maths in the lead at all? Famously Stephen Hawking said in A brief History of Time that he was warned that for every equation in the book, the readership would be halved, hence it includes only a single equation: E = mc2. If he can write a book on such a complex subject with only one equation then surely we can keep them out of the lead of an article so as not to discourage readers before they start. Couldn't we just say something to the effect of the value of B is different whether it's measured in a vacuum or a material due to the magnetization of the material? Richerman (talk) 18:11, 8 November 2017 (UTC)

Well, I agree it would be preferable to avoid equations in the introduction. RockMagnetist, could we explain the relation between B, H, and M in words? --Chetvorno^TALK 19:08, 8 November 2017 (UTC)

How about this: Aside from units, B and H are the same field in a vacuum, but in a material they are altered in different ways by the magnetization. 23:07, 8 November 2017 (UTC)

That sounds good to me. Richerman (talk) 23:35, 8 November 2017 (UTC)

I tried adding that sentence, but it seemed too vague, so I tried adding a little on their vector properties. I know it's more technical, but it's about the simplest way I can think of to bring in Maxwell's equations. RockMagnetist(talk) 22:23, 10 November 2017 (UTC)

I think the equation version was better. The current version gives some properties of B and H but does not say anything about their relationship, and nontechnical readers are not going to understand the terminology. --Chetvorno^TALK 20:52, 11 November 2017 (UTC)

I love the image you added, I never saw a graph of B and H for a magnet separately. The second image perfectly illustrates the Gilbert model of magnetism, representing H as sourced by fictitious magnetic "charges". It definitely should be in the article, but I question whether it should be the introductory image. I think it is more needed in the article body where the relation between B and H is explained. I feel the previous introductory image was better; even better might be an iron filings image of the field around a magnet. --Chetvorno^TALK 20:52, 11 November 2017 (UTC)

Either version is o.k. with me, although I think I too lean towards the first version. I'll wait to see what other people think. RockMagnetist(talk) 23:11, 11 November 2017 (UTC)

The remaining sentence that bothers me is: "In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic tensor; the split of this tensor into electric and magnetic fields depends on the relative velocity of the observer and charge." In the spirit of J Devore's complaint above, this strikes me as far too technical for the introduction. --Chetvorno^TALK 18:12, 7 November 2017 (UTC)

I think you're right. RockMagnetist(talk) 15:34, 8 November 2017 (UTC)

Took another whack at the introduction. What do you all think? --Chetvorno^TALK 22:19, 15 March 2018 (UTC)

It's more readable, but not quite accurate. Both the H-field and B-field are affected by magnetization. The B-field can be used to account for the magnetization if you express M in terms of currents. You'd have to be a masochist to that, but many EM textbooks formulate it that way. The problem is, much as users of this article would like to see a simple definition of H and B, there isn't one. They are just the fields that appear in Maxwell's equations. RockMagnetist(talk) 15:33, 16 March 2018 (UTC)

There's also that annoying business of units: in SI units, B is just proportional to H+M. RockMagnetist(talk) 15:37, 16 March 2018 (UTC)

But my wording does not say that B cannot also be used to account for magnetization, it's just that H accounts for it more conveniently.

How about "H was a field introduced to account for magnetization..."? This doesn't prescribe it's uses. I think both this and my previous wording are certainly acceptable as a prose description of H. It is consistent with the description in our Maxwell's equations article. There, the Maxwell's equations in the variables E and B are described as "the "microscopic" version of Maxwell's equations, expressing the electric and the magnetic fields in terms of the (possibly atomic-level) charges and currents present." The equations in D and H are described as "Maxwell's macroscopic equations" or "Maxwell's equations in materials". "The "macroscopic" equations separate out the bound charge and bound current...The cost of this factorization is that additional fields, the displacement field D and the magnetizing field H, are defined and need to be determined. Phenomenological constituent equations relate the additional fields to the electric field E and the magnetic B-field...". --Chetvorno^TALK 16:49, 16 March 2018 (UTC)

I guess on second thought I don't really have a problem with that statement. I think the current wording of the lead looks fine. RockMagnetist(talk) 17:01, 16 March 2018 (UTC)

While I strongly agree about simplifying the lead. Some of the changes are causing more trouble than they are solving IMO. For example the use of the term 'force field' is neither true nor enlightening or even simple. I am going to try to work on the lead some focusing on 1. keeping it simple, 2. keeping it so that it reflects what is covered in the article, 3. keeping it as complete as possible, and 4. keeping it short. I realize that these are all competing (and often contradictory) goals. I am mentioning this as a warning that my changes might make things worse before it makes them better. I will keep in contact here. TStein (talk) 17:27, 10 April 2018 (UTC)

I think some of TStein's recent changes to the introduction are improvements, others I disagree with:

• I don't like the new lead sentence: "A magnetic field is a quantity that describes the magnetic influence at a given point due to nearby electrical currents and magnetized materials." This is a step back to the type of lead we had before, a vague tautology which gives readers no information. I agree that the term "force field" in the previous lead was not very good, but I think the wording should somehow say that magnetic fields exert force.
• I like the new sentence contrasting H and B: "H and B differ in how they account for magnetization." This is better than my previous sentence, which RockMagnetist quite rightly pointed out was not really accurate.
• I like that the sentence "In everyday life,..." is moved up closer to the top, so general readers will see something they can recognise right away, amid all the strangeness.
• "Magnetic field surround and is created by magnetized material..." seems to be a grammatical mistake?

I know but I have a hard time deciding when magnetic field should be singular or plural. I am going to have to defer to others. TStein (talk) 21:25, 18 April 2018 (UTC)

• "Magnetic fields exert...torques on nearby magnets." They also exert forces on them.

My reasoning was that the force on magnets was due to difference in magnetic fields (a magnet in an perfectly uniform magnetic field experiences no force). Further, I believe that it is covered in the lead soon after. TStein (talk) 21:25, 18 April 2018 (UTC)

--Chetvorno^TALK 22:03, 11 April 2018 (UTC)

I support Brian Everlasting's reversion of TStein's replacement of the term "vector field" with "quantity" in the lead sentence. TStein's lead sentence: "A magnetic field is a quantity that describes the magnetic influence due to nearby electrical currents and magnetized materials", besides not giving any substantive information about the subject, will be misleading for general readers as it describes a magnetic field as a singular "quantity" - it is 3 quantities defined at each point in space. We define "vector field" a few sentences down in the lead paragraph, so I don't think it will be too confusing to use the correct term in the lead. ----Chetvorno^TALK 20:12, 18 April 2018 (UTC)

Chetvorno: thanks for your input. I never feel one hundred percent comfortable with any of my changes. It is an iterative process. To some extent I agree that the first sentence is 'vague tautology' but on the other hand it gives a starting point for which to add the rest of the paragraph. I believe that we risk alienating non-technical readers if we get to technical terms like vector field too quickly. My choice was to start off vague and add complexity at a reasonable pace. Other choices may work better. But, I feel that making the first sentence more vague has allowed the first paragraph to be better as a whole. TStein (talk) 21:25, 18 April 2018 (UTC)

Thanks for all the great comments. It seems to me that User:TStein and User:Chetvorno, (and everybody else) are doing a good job so far with this article. I understand the argument that this article is too technical for beginner readers to understand, but over simplification may lead to factual errors. Also, vector calculus and vector field are subjects not normally covered in high school curriculum. Further complicating the situation is the fact that some students learn "non-calculus based physics" while other students learn "calculus based physics". For a non-calculus based physics student, TStein's argument "quantity" makes more sense. So maybe we need another non-calculus based article on Magnetic Field like "Introduction to Magnetic Field", or maybe just a new section in the existing article for non-calculus based explanation? Or maybe we should list prerequisite articles at the top of this article like: "WARNING, don't read this article unless you have already read calculus, line integral, cross product, vector field". Although physics and calculus are very closely related, many concepts in physics can be explained to a high degree of accuracy without calculus. Brian Everlasting (talk) 22:01, 18 April 2018 (UTC)

Brian Everlasting: Having both a technical and non-technical version of this page is probably way too much effort to maintain and to keep distinct and to get the right audience to the right page. I believe that the best approach is to start off as least technical as possible and to build up what is needed when it is needed. A good overview can be useful for both the technical and the non-technical. Stating technical facts can sometimes serve neither user as it simultaneously confuses the non-technical user and merely restates what the technical user already knows in the same way they have heard it a thousand times over. TStein (talk) 22:55, 18 April 2018 (UTC)

Brian Everlasting: Personally, I like the challenge. Any expert can make an article near perfectly complete and correct. Any educator can make an article near perfectly accessible to the nontechnical reader. Any professional writer can make an article near perfectly concise and interesting. Unfortunately, it is impossible to do all three perfectly; perfection in any 2 comes at the expense of the third. That is why articles like this one are so difficult; it really needs to be as excellent as possible at all three. I have confidence that it is gradually getting to where it needs to be thanks to editors like you and everyone else who works on this page. TStein (talk) 22:55, 18 April 2018 (UTC)

Impressive to see the efforts to achieve the impossible. Naive query/suggestion: If the idea is to reach both technical and non-technical audiences, then maybe the "lead section" should have "technical" (presupposing physicists conceptual language/frame) and "non-technical" subsections? Or in any case to have a clear marking of when the text is being informal, qualitative, and when it is switching to using the technical language/concepts that physicists are using to explain/understand/interpret the phenomena. I can elaborate if this sounds interesting. Sdc870 (talk) 04:40, 20 April 2018 (UTC)

I know that I started it but this is in my opinion way overthinking the problem. (Just like I was overthinking the problem earlier.) TStein (talk) 15:35, 20 April 2018 (UTC)

@Sdc870: I pretty much agree with TStein. However I appreciate your viewpoint. It seems to me the introduction is already sort of divided into a "technical" section, paragraph 2, and "non-technical" section, which is the remainder. Maybe the wording of the nontechnical parts can be improved. ----Chetvorno^TALK 18:12, 20 April 2018 (UTC)

@TStein: @Chetvorno: I accept your points.

Here are some more suggestions.

1. For first sentence, add underlined: In physics, a magnetic field is a vector field that describes the magnetic influence due to nearby electrical currents and magnetized materials.

Reasons: (a) gives contrast (and uses parallel form) to next sentence, which starts ‟In everyday life”, (b) makes clear that ‟magnetic field” is being used here as a technical term, which justifies it being named as a vector field. Sdc870

I don't really think it's needed since the term "magnetic field" does not have a second usage in some other area of study, but I have no objection to the addition. Where that phrase is really needed is in the first sentence of the second paragraph: "In physics, the term 'magnetic field' is used for two distinct but closely related fields denoted by the symbols B and H." (or "In electromagnetics...").--Chetvorno^TALK 22:59, 21 April 2018 (UTC)

2. For second sentence in 1st para (add underlined, delete struck through): In everyday life, the effects of magnetic fields are most readily encountered with seen by the force created by permanent magnets, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets.

This would result in: In everyday life, the effects of magnetic fields are most readily encountered with permanent magnets, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets.

Reason: Should be obvious, but I can explain if needed. Sdc870

3. Last sentence in 1st para. seems redundant – ‟As such, it is an example of a vector field” – given that the vector field is mentioned in the first sentence. Sdc870

My feeling is that since the mathematical term "vector field" must be used in the introduction (particularly since it is in the lead sentence), there needs to be a brief description of what a vector field is, for nonmathematical readers. This sentence fills that need. --Chetvorno^TALK 22:59, 21 April 2018 (UTC)

@Chetvorno: Ok. I understand the intent now. Are you assuming that a nonmathematical reader knows what a vector is, and just needs to understand 'vector field'? Meanwhile, the referents of "As such" and "it" in that last sentence are ambiguous. Here is an attempt to address that problem by combining the two sentences: "Viewed as a vector field, the magnetic field describes the strength and direction of magnetic force for different locations within the field" (My reasoning is that even if someone does not know what a vector is, or vector field, they may be able to understand that the magnetic field describes strength and direction in different locations. (Also, take a look at the word "location" in the present formulation. If a person does not understand the field idea, then the sentence could be read as though the location of the (entire) field, rather than location within the field. Ok. I leave the rest to you. Sdc870 (talk) 04:05, 24 April 2018 (UTC)

4. Maybe sentence in third para that starts: ‟Magnetic fields are produced by moving electric charges….” should be moved up to the first paragraph and combined with the sentence that starts ‟Magnetic fields surround and are created by ...” (because they are both explaining how magnetic fields are produced). And if that happens, then perhaps the other sentence in the third para. (about interrelation of electric and magnetic field will follow along). Sdc870

I don't have any real concerns with any one of these except for including the term 'in physics'. Both the B and H fields are used by a very broad range of fields outside of physics. My main concern is that many little improvements can make the whole worse. A slightly longer and more precise word here, a little more explanation there, a little more symmetry of the sentence structure someplace else; they are all good things individually but each of those can add a little extra burden to the lead as a whole. Every artist knows that it is important to tweak to make things a little more perfect; but every artist also knows that there is a time where need to step back. Brevity, simple language, and avoiding complex terms and concepts until absolutely needed are also virtues. TStein (talk) 23:50, 21 April 2018 (UTC)

@TStein: Have I interpreted correctly, that I can try to enter some of these changes -- and then you can see how it looks? I do not think I have other proposals beyond what is already given here. Sdc870 (talk) 04:05, 24 April 2018 (UTC)

Sdc870: hehe. On wikipedia it is holier to ask forgiveness than permission. I don't own this page. Do whatever you think you need to do. Don't worry, if you were a crackpot or if you obviously did not understand the material or if you were wanted to make the page too technical I (and others) would be much more assertive. I am curious what it will look like when you are done. It would not be the first time that someone else's vision turned out to be better than mine. But there is no way to know until it is done. TStein (talk) 05:35, 24 April 2018 (UTC)

TStein: Ok. I will try some things. But it has also been informative to get responses here. And given that you and others have spent some time thinking about it, then I can get the benefit of your experience (e.g., there may be some reasons behind choices that I did not perceive). Sdc870 (talk) 03:36, 26 April 2018 (UTC)

And a new query about the first sentence. Is there a special reason for "influence" in the first sentence? Otherwise, my proposal:

A magnetic field is a vector field that describes the magnetic influence force due to nearby electrical currents and magnetized materials.

And right now the first sentence emphasizes the vector field. From a more everyday perspective, wouldn't one expect that the field is the "magnetic force in different locations (in a bounded region)"? Are there strong opinions that have already been resolved about whether the opening sentence should highlight the magnetic field as "physical phenomenon" or as "mathematical construct"? It may be possible to do both indicate both. For example:

A magnetic field refers to magnetic forces in a region of space close to an electrical current and/or magnetized materials. The strength and direction of the magnetic force for each location in the region can be described mathematically as a vector field.

This version might also address the issue discussed above in point 3. Comments? Sdc870 (talk) 03:36, 26 April 2018 (UTC)

The reason to use "influence" instead of "force" is this article discusses 3 different but easily confused vector fields: the B, the H, and the F. If we say force, that would imply that magnetic field is only F, which is not true. I also disagree with your proposal to remove vector field. Brian Everlasting (talk) 03:51, 26 April 2018 (UTC)

Brian Everlasting: I agree with not using the term force for the reason you mentioned. TStein (talk) 05:57, 26 April 2018 (UTC)

Sdc870: To add to Brian Everlasting's point, I disagree with the term 'close' because magnetic fields often extend for great distances. I know that is also a flaw in the original sentence (which I had a hand in writing) as well but IMO this makes that flaw worse. That being said, it is good that you are trying to fix the flaws in the lead not the least because it is a very difficult job. For example, if you want to cringe just google 'definition of magnetic field'. Sometimes editing a lead is like a classic physical humor routine, every attempt to avoid one pratfall seems to lead to hitting 3 others and every step seems to land on a banana peel or a rake positioned just right to smack you in the face. TStein (talk) 05:57, 26 April 2018 (UTC)

Thanks TStein. The reason I was OK with keeping 'close' in opening sentence is that far away magnetic fields are negligible in many applications. On the other hand, your wording is good because it really describes the magnetic field as a universal rather than just for close stuff. Brian Everlasting (talk) 04:03, 28 April 2018 (UTC)

TStein: Thanks for your gemütlich explanations. I am encouraged that my queries seem to inspire substantive improvements. So here is another proposal for the first two sentences, that tries to incorporate achievements in relation to the first, while trying to help non-technical readers. Sdc870 (talk) 11:34, 29 April 2018 (UTC)

A magnetic field refers to a region of magnetic influence by electrical currents and magnetized materials. The strength and direction of influence for each location in the region can be described mathematically as a vector field.    Sdc870

The usage of the term "refers to" in the lead is discouraged, see WP:REFERSTO. The magnetic field "is" a region of magnetic influence. With that change I think the first sentence is better than the current one; describing the magnetic field as a "region" is better than using the mathematical term "vector field" in the lead. I think the second sentence could be improved; maybe "The field has a strength and direction at each point and so is described mathematically as a vector field. --Chetvorno^TALK 15:23, 29 April 2018 (UTC)

However I'd like to see the word "forces" used in the lead sentence instead of "influence". I disagree with Brian Everlasting's point above. Physically speaking, there is only one magnetic field. We do not speak of the "magnetic fields" of a magnet. The vector fields B and H are alternate mathematical descriptions of a single magnetic field. The main effect of a magnetic field (the only effect if you include induction forces due to the electric fields $\nabla \times E$ created by time varying magnetic fields) is to exert forces (including torques) on charged particles and magnetic dipoles. Here are some examples of definitions used in the literature; notice that they all use the word "force":

• "Magnetic field, region in the neighbourhood of a magnet, electric current, or changing electric field, in which magnetic forces are observable" (Encyclopaedia Britannica online)
• "Magnetic forces are described by means of the magnetic field, which is a vector quantity which possesses a value at every location in space and can vary with time" (Rosen, Encyclopedia of Physics)
• "Magnetic field, a vector field occupying physical space wherein magnetic forces may be detected..." (Academic Press Dictionary of Science and Technology)
• "Magnetic field, a field of force associated with changing electric fields, as when electric charges are in motion." (The American Heritage Science Dictionary)

--Chetvorno^TALK 15:23, 29 April 2018 (UTC)

Thanks everyone, especially Chetvorno, for the great ideas. I was bold and updated the article using the suggested material. Feel free to make it better. Brian Everlasting (talk) 18:26, 29 April 2018 (UTC)

Magnetic field is neither a region nor a force

I disagree very strongly with the last edit and I don't know how to fix it. I have two problems with it. First, magnetic field is not a region nor is magnetic field limited to a region. Magnetic fields literally extend for as far as the eye (or telescope) can see. Second, and just as important the association of magnetic field with the word force is extremely misleading. The Lorentz force only applies to moving charges and forces on magnetic materials only occur for a non-uniform magnetic fields. Further, the integral of Bdl does not equal work done, etc. I realize that respected dictionaries use these terms, but it doesn't make it any less awful. TStein (talk) 21:02, 29 April 2018 (UTC)

Thanks to Chetvorno for interesting input/debate in previous discussion section, including nice illustrations of TStein's point that others can also make less-than-ideal definitions. Here is some more unpolished, raw material that might offer or inspire a way out of the gridlock -- at least in relation to the "region" question -- by simply avoiding to mention it. (when I used it, I was considering that a region can also be infinite...) This proposal does not address the "influence" vs. "force" debate. For now I have used "influence" (because something had to be used), but no prejudice is intended. (I also changed "electrical currents" to "moving electric charge" and added "permanently" to "magnetized materials" — for the sake of nontechnical readers). (I anticipate objections to "always observed" -- but will wait with explanations.) Sdc870 (talk) 10:03, 2 May 2018 (UTC)

Magnetic field is the physical phenomenon of the magnetic influence always observed with a moving electric charge and permanently magnetized materials. The strength and direction of the influence for each location in space, relative to the charge or magnetized material, is described mathematically as a vector field.  Sdc870

So, TStein, no objections? And if I introduced this text, you would not undo it? Sdc870 (talk) 22:32, 19 May 2018 (UTC)

Sorry, Sdc870, but I object. That is really awkward wording. Anyway, what is the problem with the current wording? RockMagnetist(talk) 05:19, 20 May 2018 (UTC)

"The first sentence should tell the nonspecialist reader what, or who, the subject is." MOS:FIRST

Much of previous discussion here elaborates various problems with first sentence (e.g., "vector field").

RockMagnetist What do you find awkward? Sdc870 (talk) 11:32, 10 October 2018 (UTC)

Sdc870, sorry, I also feel your version is not as good as the current wording, it just uses more words without adding information. The phrase "the physical phenomenon of the magnetic influence" is confusing. The definition of "vector field" currently in the first paragraph is more succinct and clear than yours. --Chetvorno^TALK 19:43, 10 October 2018 (UTC)

I see now the awkwardness in my proposal. But let me ask for a clarification: Is magnetic field supposed to refer to "vector field" (a mathematical construct) or "magnetic influence" (a physical phenomenon)? As I read the current first sentence, it refers to a mathematical construct (but not to a physical phenomenon). Is that the intention? Thanks. Sdc870 (talk) 20:31, 10 October 2018 (UTC)

As far as I can see, the whole first paragraph, when read in its entirety, addresses the issues that concern you. Attic Salt (talk) 21:59, 10 October 2018 (UTC)

I agree that the article as it stands is better than the proposal. I understand the discomfort with vector field in the first sentence, but I think it's useful to have those words there. Ccrrccrr (talk) 23:23, 10 October 2018 (UTC)

Magnetic pole model confuses

I believe that the section on the Gilbert magnetic pole model is not helpful as it stands. It may be of historical interest, but some of the statements in it are just plain wrong. No distribution of hypothetical magnetic "charges" can reproduce the field around a current carrying wire or solenoid, and it is not true that the H and B fields are antiparallel within a magnetic material. Even in the case of the external field around a magnetic dipole magnet, I believe the magnetic pole model only gives a qualitative approximation of the field. The model itself is inconsistent with the Maxwell equation stating that the divergence of the magnetic field is always zero. It isn't sufficient to acknowledge that magnetic monopoles have never been found, and say that the magnetic pole model of fields is merely "conceptual". It cannot give accurate quantitative results, and the misstatement about B vs. H within a magnetic material has caused a good deal of confusion about the subject. 73.93.173.170 (talk) 22:56, 24 June 2018 (UTC)

It's of more than historical interest because everyone who models magnetic domains in ferromagnets uses poles (but they don't call it the Gilbert model). You're right about there being a lot of inaccuracies, not to mention a lack of sources. I'll try to find time to rewrite it. RockMagnetist(talk) 00:20, 26 June 2018 (UTC)

I have been digging into this a bit more, and as far as I can tell the only author who refers to the magnetic pole model as the "Gilbert model" is David J. Griffiths (in his textbook on electromagnetics and other publications). It's not even clear which Gilbert he is referring to - is it T. J. Gilbert of the Landau–Lifshitz–Gilbert equation? So much for the historical interest. I think the reference to Gilbert should be dropped, here and in Force between magnets. But to clarify something I said above - the inaccuracies are in this article, not the model. Used correctly, the magnetic pole model gives the same results as the current loop model, but with less effort. I have plenty of sources to back this up, and I'll rewrite the section soon. RockMagnetist(talk) 18:03, 26 June 2018 (UTC)

I have to confirm RockMagnetist. An appropriate distribution of hypothetical magnetic "charges" can totally reproduce the precise magnetic field of a magnet, where there is no free current. This is because $\nabla \cdot \mathbf {H} =-\nabla \cdot \mathbf {M} =\rho _{m}$, so the H-field originates from the bound magnetic charge $\rho _{m}$. The charge $\rho _{m}$ is located where the magnetization changes ($\nabla \cdot \mathbf {M}$), that is at the end of the magnet. And if H can be calculated, then B can be as well via $\mathbf {B} =\mu _{0}(\mathbf {M} +\mathbf {H} )$. Now if there is free current, such as in a current carrying wire or a solenoid, the pole model may be helpful in some cases and not in others. The B-field of an ideal solenoid can be perfectly calculated with an uniform charge distribution on the solenoid's plane end facets, and later subtracting a constant M-field within the solenoid volume (see magnetic field of a cylinder magnet for an accurate example). For other configurations, such as a simple wire, no appropriate magnetic charge distribution might be found. However, I would also not call the pole model "Gilbert model", because that term doesn't seem to be widespread. --Geek3 (talk) 13:06, 18 January 2019 (UTC)

Should "magnetic influence" redirect to this article?

The phrase magnetic influence appears in the first sentence of this article (after which influence does not appear again in the article). A search in Wikipedia on "magnetic influence" redirects to "Magnetic pistol". Maybe "magnetic influence" should redirect to here? Sdc870 (talk) 23:53, 19 March 2019 (UTC)

The target should definitely not be magnetic pistol, a pretty obscure subject. I tried Googling "magnetic influence", and the top few hits were to some huckster called Dani Johnson. After which the next hit was Magnetism. So maybe that's the best choice. RockMagnetist(talk) 02:42, 20 March 2019 (UTC)

Maybe it needs to be marked as "magnetic influence (physics)" [though have not found it mentioned in textbooks] to differentiate it from this definition: (2009) magnetic influence. In: Manutchehr-Danai M. (eds) Dictionary of Gems and Gemology. Springer, Berlin. https://doi.org/10.1007/978-3-540-72816-0 :

"a believing that magnetite or magnetic power promotes the user to be straight forward, reality oriented, etc."

Also, right now, the Magnetism article does not address 'magnetic influence' directly, so it would be necessary to modify that article, if redirected there.

Sdc870 (talk) 09:51, 21 March 2019 (UTC)

I don't think such information would be appropriate on that page. A disambig page would be better. RockMagnetist(talk) 14:39, 21 March 2019 (UTC)

That is also what I was trying to suggest with "magnetic influence (physics)" (but I do not know how to make a disambiguation page). My other point was that right now the Magnetism page does not provide clear information about "magnetic influence (physics)". Did not mean to imply that the superstitious meaning should also be discussed. Sdc870 (talk) 15:00, 21 March 2019 (UTC)

"Magnetic pistol" isn't a terrible target choice for Magnetic influence, which is a common term for a class of naval weapons that are activated by magnetic fields. All 3 of the existing links to that redirect are correctly retargeted to magnetic pistol. There would be no pointto creating a parenthetically disambiguated redirect. VQuakr (talk) 15:53, 21 March 2019 (UTC)

Yes, the more I look into this the more I am leaning towards that point of view. In a search of uses of the term in Wikipedia, almost all refer to the military use. In physics articles, it's just a vague term that should probably be replaced by a more precise term. RockMagnetist(talk) 16:10, 21 March 2019 (UTC)

The expression has been used in non-military scientific texts for over 100 years: examples of the use of the phrase ‟magnetic influence” in physics journal articles, but more or less impossible to find in textbooks. Perhaps the word "influence" has to be removed or defined in the first sentence? Sdc870 (talk) 17:13, 15 April 2019 (UTC)

This seems to me to be an example of overdefining of terms ("redirect overkill"). Looking at the links given, I don't see that the term has a specific meaning, but as RockMagnetist says is a vague term whose meaning varies by context. Making it redirect to a specific article is implying a specificity of meaning that it doesn't have. I'd suggest deletion. --Chetvorno^TALK 12:11, 16 April 2019 (UTC)

I think a conversation about what to do with the redirect should be moved over to its talk page (or maybe Wikiproject Physics). As far as this article is concerned, we should begin by delinking it and then come up with a better wording. RockMagnetist(talk) 15:00, 16 April 2019 (UTC)

Correction: it isn't linked. I don't know why I thought it was. RockMagnetist(talk) 15:01, 16 April 2019 (UTC)

(copied this discussion to Talk:Magnetic influence#What should the target of this redirect be?)

Manipulation

Shaping of magnetic fields?? It seems there exists technology that allows to shape magnetic fields. Setenzatsu (talk) 22:34, 9 June 2019 (UTC)

Since ferromagnetic materials like iron have greater permeability than air, magnetic fields preferentially pass through these materials, so magnetic cores of iron and ferrite are used to guide magnetic fields. Materials of even greater permeability like mu-metal are used for magnetic shielding, which conducts magnetic field lines around areas in which magnetic fields are not wanted. --Chetvorno^TALK 23:46, 9 June 2019 (UTC)

Alternative names???

"Magnetic field" and "magnetizing field" are NOT alternatives for H. These are just the names "we" gave to these physical phenomena. H is a DESCRIPTION of these phenomena, but it's not the phenomena themselves! — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 14:20, 4 June 2019 (UTC)

Are you proposing a change in wording? If so, where? RockMagnetist(talk) 16:52, 4 June 2019 (UTC)

Let's call H the magnetic field and B the effective magnetic field, depending on the medium. — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 12:26, 17 February 2020 (UTC)

The both H and B are casually called the magnetic field in reliable sources. However, when reliable sources make a distinction between them, H is called magnetic intensity and B is called magnetic flux density. Constant314 (talk) 13:11, 17 February 2020 (UTC)