Talk:Electromagnet

Left-hand rule vs Right-hand rule

I changed the part about the left-hand rule giving the direction of the magnetic field inside a solenoid - definitely not the case! Magnetic flux inside a solenoid follows the right-hand rule. (I'm sure one or two people got one or two answers wrong in their test!) —The preceding unsigned comment was added by 125.237.23.198 (talk) 08:39, 9 May 2007 (UTC).

Your Dates Were Way Off

Excuse me for being vociferous, but William Sturgeon died in 1850. Yes, he did invent the electromagnet. He actually invented much earlier than you indicated. He invented it in 1823. Michael Faraday wouldn't have been able to create his electric motor in the 1830s if William Sturgeon hadn't invented the electromagnet in 1823, because an electromagnet is one of the essential components of an electric motor. In 1837, Samuel Morse invented the electromagnetic telegraph, which is an electromagnet that pulls an iron tapper towards it when an electric current is flowing through the wire. The electric telegraph is an electromagnet that creates clicks by pulling an iron tapper. This tapping is similar to the clicks produced by the electromagnetic relay, which was invented in 1835 by Joseph Henry.

The electromagnet was invented long before the year you had written.

Electromagnets&school

This site doesn't have enough data for our school project on electromagnets.

Try using other sources. --Smack (talk) 22:26, 12 May 2005 (UTC)

This attitude is the very reason why Wikipedia is sooo useless. That is why people don't donate: we can't use it.
Here, it doesn't show how to calculate the force excerted on a piece of iron by the magnetic force at 'd' distance from the coil. All academic bull, no practical use. — Preceding unsigned comment added by 115.70.177.64 (talk) 13:53, 16 July 2013 (UTC)

If someone could come up with some drawings and images, I can do the math. Something simple, like a U-bolt from a hardware store would be nice. Or simpler yet, a square core with one end cut off. Please don't include the standard nail example -- it's way too hard to analyze in closed form. Here are a couple of example from Edmunds Scientific. Madhu 00:13, 31 October 2005 (UTC)

If you're talking about a closed magnetic circuit, such as an electromagnet of wire wound on a U-shaped bolt picking up a steel plate bridged across its poles, eq. (1) and (2) in the article can be used. You can calculate the magnetic field B from the number of turns and the current using eq. (1) if you measure the length of the looping magnetic path L through the bolt and the plate, provided you can find the magnetic permeability μ of the steel. Then eq. (2) will give you the force exerted by each pole face on the steel plate, from the area A of the pole face. The main problem will be finding the permeability of the steel. I'd just go on the Internet and use a value for mild steel. It won't be very accurate, but you will be within a factor of two. --Chetvorno^TALK 14:32, 16 July 2013 (UTC)

Applications

I think an intereseting application of electro-magnets is in its use as a weapon, namely rail guns.

Yeah, the incredibly high magnetic field needed to make a heavy object shoot out of the electromagnet will leave tumours in your brain, apart from killing another person with the weapon, but why use springs or air pressure or maybe even gunpowder in your gun for a better, cheaper, safer result, not to mention the exclusion of the necessity to plug your "weapon" into a wall socket. How about junkyards? They seem to lift pretty heavy objects with those electromagnetic cranes. Slartibartfast1992 23:51, 13 March 2007 (UTC)

Another place of use in the ag industry are in electric clutches so pumps or shafts can be turned on and off immediately with the flick of a switch. — Preceding unsigned comment added by Kenton007 (talk • contribs) 13:49, 5 May 2013 (UTC)

who

who made this page

Lots of people. See the history page. --Smack (talk) 05:11, 6 October 2005 (UTC)

Force on Ferromag Materials calculation?

The force per unit area is given in lbft/in², when all the quantities that go into the calculation are in SI. If I do the calculation in SI units, the F/A comes out to 398 kN/m² for the 1 Tesla case.

Does anyone else agree that we should have consistent units all the way through those calculations? --Syrthiss 02:58, 28 October 2005 (UTC)

Sure, include the SI numbers. The only reason I used mixed units is that most people don't have a feel for what a kN/m^2 (kPa) is. All I ask is that you keep the mixed unit numbers since it's easy to get your head around PSI. Think of it this way: I need to lift 50 pounds, how big of a magnet do I need? 1 Tesla is a reasonable number for flux density, so a square inch is in the ballpark. In SI, 50 pounds (force) is about 200 N, so you would need some very small area in m^2. Square centimeters would be easier, a centimeter is easy to guestimate. I like to run numbers in my head or the back of an envelope... Madhu 00:05, 31 October 2005 (UTC)

I think we should insist on SI. Add American units in parentheses if you want, but it's counterproductive to perpetuate them. --Smack (talk) 22:43, 11 November 2005 (UTC)

WHERE is the calculation of force exerted on ferromagnetic magetic material across an air gap???? I've looked everywhere and I can't find it.

Thecoolsundar (talk) 07:28, 15 August 2010 (UTC)

Another question

Come to think of it, what is this section doing in an article on electromagnetism? Shouldn't it be somewhere else, like ferromagnetism? --Smack (talk) 04:59, 16 November 2005 (UTC)

Well, I think he was using it as a basis for how to calculate the turnings and such an electromagnet would need to develop a field of XX strength. So, yes it could be used in Ferromagnetism but also seems applicable here. That reminds me though, I need to put in the SI calculations. Then we can still consider whether to move it or leave it here. --Syrthiss 05:32, 16 November 2005 (UTC)

Done. I just looove Mathcad. It has to be one of the greatest software applications ever developed. Madhu 01:48, 17 November 2005 (UTC)

Thanks :) --Syrthiss 04:44, 17 November 2005 (UTC)

could you tell me more about magnetic calculations?thanking you,rudrakshm@pathways.ac.in

Sure, it's simple. The fundamental definition of energy is force times distance. The energy in a magnetic field can be derived from first principles, you can find that in any electromagnetics text. Fields and Waves in Communication Electronics by Ramo, Whinnery, and Van Duzer is an excellent book. If you have a magnetic field of a known field strength, you can calculate the energy of that field. If anything is added to that field that changes the field strength, the energy changes. To change the energy requires a force, which is energy divided by change in distance (or dE/dx to be more accurate). I assumed the field was in air, but it could be in any medium. The derivation is in Magnetic_field Madhu 17:25, 18 November 2005 (UTC)

I need to create a electrical magnet that can preform the operations od a linear actuator EG propel the inner rod with reasonable force but not exceeding the stroke. I do not waht the rod to fly out im trying to achieve a popper like motion when a current is applied can anyone help?

Remanent magnetism

The article should include something about remanent magnetism.

What happened to the image?

What happened to the cool image of an industrial lifting electromagnet? Why was that removed? Madhu 20:50, 11 August 2006 (UTC)

Higher ampere-turns

You say there is no point in using more than 787 A-turns per metre (not sure exactly where this figure comes from), because of saturation of the electromagnet core. However this only happens when the air gap of the magnet is closed. If you want to project a large field into an air gap, rather than just hold onto a chunk of iron, then I think you can usefully use a far larger mmf per length of core because the dominant reluctance of the air gap lowers the H field.

Simon80.41.41.166 23:37, 31 August 2006 (UTC)

That value is rougly the saturation field intensity for steel. You are correct about projecting large fields into an air gap. Feel free to adjust the wording as appropriate. Madhu 03:08, 1 September 2006 (UTC)

Done. --Chetvorno^TALK 19:30, 27 September 2008 (UTC)

What about force between Electromagnets

Somebody Please include the description on force calculation between the electromagnets ( attractive or repulsive ).

vijay anand

WP:SOFIXIT. --Slartibartfast1992 19:26, 11 February 2008 (UTC)

field redirection?

Does anyone know how one could block the field in one direction and/or amplify the field in the other direction? 71.185.202.190 (talk) 22:19, 1 May 2008 (UTC)

Possible error: paramagnetic core?

The Introduction section says Much stronger magnetic fields can be produced if a "core" of paramagnetic or ferromagnetic material (commonly soft iron) is placed inside the coil. Paramagnetic? I've never heard of a paramagnetic material being used for the core of an electromagnet, at least not to increase it's permeability. Yes, a paramagnetic material would produce a slightly greater H than no core, but the increase is of the order 10^-5, totally negligible. Even if paramagnetic cores have been used for some specialized research purposes, I think it is misleading to list it next to and on an equal basis with 'ferromagnetic'. All ordinary electromagnets use ferromagnetic cores. Unless there's a good reason for leaving it in, I'm going to delete it. --Chetvorno^TALK 05:52, 9 August 2008 (UTC)

Done --Chetvorno^TALK 23:33, 12 August 2008 (UTC)

Citations

I am doing a year 13 (grade 12) physics paper, and must cite where i get any outside equations. Rather than cite wikipedia, does anyone have specific links to where these equations are derived or stated? Especialy the ones for a closed magnetic cercuit and force between electromagnets. - Josh, UK. —Preceding unsigned comment added by 90.219.63.103 (talk) 17:59, 3 November 2008 (UTC)

Air gap?

Where? Air gap between turns? Air gap between winding and core? Air gap between sections of core? The latter makes sense from the discussion but isnt at first obvious. All terms should be clarified with a diagram or description, as one does with an equation. Small ambiguities can lead to hours of futility for a practical desighn engineer where accurate information has to be applied to create working systems. —Preceding unsigned comment added by Q5101997 (talk • contribs) 02:48, 17 December 2008 (UTC)

Thanks, you're right, that's unclear. Its the air gap between sections of the core. I was going to include a diagram of an electromagnet illustrating air gaps, fringing fields, and leakage flux, but didn't get around to it. --Chetvorno^TALK 03:31, 17 December 2008 (UTC)

Added diagram clarifying the above terms. --Chetvorno^TALK 15:01, 6 October 2010 (UTC)

Reply to Air Gap?

Your article was very informative and accurate. The use of diagrams and explanations of terms is imperitive. Contininuue to elaborate on this and it will be a fine and usefull article. 124.177.127.47 (talk) 10:56, 22 December 2008 (UTC)

hi —Preceding unsigned comment added by 99.251.238.177 (talk) 14:24, 6 February 2010 (UTC)

Removal of content in "Ohmic heating" section

A 15:59, May 14 edit by 94.237.95.24 removed the discussion of minimum heat dissipation in the "Ohmic heating" section with this comment: "It was forgotten that when N increases -> also R increases due to increased length. Further analysis based on this misconception all removed." I reverted this removal; the original content was correct. Below is a derivation of the disputed point: that the ohmic heat losses in an electromagnet can be reduced by increasing the number of turns and proportionately decreasing the current, but that there is a minimum imposed by the area available for the windings. This is shown in many texts on electric machinery; I'll try to find a source.

The total resistance R of a DC electromagnet's windings is given by:

$R={\frac {\rho L}{a}}={\frac {\rho Nl}{a}}$

where $\rho$ is the resistivity of the wire, $L$ is the total length of the winding, $l$ is the average length of one turn, $N$ is the number of turns, and $a$ is the cross-sectional area of the wire. So the total power dissipation $P$ due to ohmic heating is:

$P=I^{2}R=I^{2}{\frac {\rho Nl}{a}}\qquad \qquad (1)$

As discussed in the article, the magnetic field produced by the magnet is a function of the magnetomotive force ${\mathfrak {F}}=NI$ so $N$ and $I$ can be varied to minimize the power dissipation as long as their product is constant. Substituting for $I$ into (1):

$P=\left({\frac {\mathfrak {F}}{N}}\right)^{2}{\frac {\rho Nl}{a}}={\frac {{\mathfrak {F}}^{2}\rho l}{Na}}\qquad \qquad (2)$

So the power dissipation is inversely proportional to $N$. Thus the heat losses can be minimized by increasing the number of turns, while decreasing the current proportionally to keep ${\mathfrak {F}}$ constant. It would seem that the dissipation could by reduced indefinitely this way. However the product $Na$ in the denominator is equal to the cross-sectional area of the winding (ignoring insulation thickness and wasted space). It increases with $N$. There is some limit to the area available between the arms of the core for the winding, call it $A$. Therefore $Na\leq A\,$. Substituting (2) into this:

$P\geq {\frac {{\mathfrak {F}}^{2}\rho l}{A}}$

This is the minimum ohmic heat dissipation of a resistive electromagnet. To show that the minimum dissipation increases with $B^{2}$ the Faraday law expression for a closed core electromagnet (eq. (1) from the article) can be used:

$NI={\mathfrak {F}}={\frac {B}{\mu }}$

So:

$P\geq {\frac {B^{2}\rho l}{\mu ^{2}A}}$

--Chetvorno^TALK 05:15, 16 May 2010 (UTC)

"Loudsmpeakers?"

I can't seem to correct this error in the first paragraph. Anyone with more Wiki mojo want to try? Pammalamma (talk) 03:59, 20 November 2010 (UTC)

Image

Perhaps that

File:Induction motor windings for electromagnet.png

the image to the right can be added to this article ?

91.182.255.53 (talk) 14:39, 2 February 2011 (UTC)

No. They would add nothing, it's also confusing (you were told this just a couple of days ago) to describe motor field coils as "electromagnets" (although they are, they're used to generate a field which reacts wiith another field, not for their simple attractiveness to magnetic materials). Andy Dingley (talk) 15:01, 2 February 2011 (UTC)

I've also tagged the image for deletion - or maybe we should categorize it under "impossible objects"? Is that bottom-left coil a left- or right-handed helix? Andy Dingley (talk) 15:25, 2 February 2011 (UTC)

Force between electromagnets

Can someone put in what the terms of the force between electromagnets refer to. It might seem intuitive but i cant figure out whats 'A'. I assume it has to be an area but what area? 59.191.202.234 (talk) 02:27, 26 February 2012 (UTC)

And also there is no mention of the Ampere model in that section Malithyapa (talk) 02:28, 26 February 2012 (UTC)

A is the cross-sectional area of the magnetic pole, which is the cross sectional area of the core; see the "Definition of terms" box at the end of the article. The "Ampere model" is primarily a way to explain how permanent magnets work and the term isn't used much with electromagnets. --Chetvorno^TALK 02:55, 26 February 2012 (UTC)

Edit request on 19 March 2012

Add iw link Fi:Sähkömagneetti Jawacz (talk) 18:54, 19 March 2012 (UTC)

Done - completed. Keith D (talk) 21:30, 19 March 2012 (UTC)

Electro-permanent magnet

I expected to find something about electro-permanent magnets in this article ... are they called something else here, perhaps? quota (talk) 07:21, 6 April 2012 (UTC)

Force between electromagnets

In the section for force between electromagnets, the force calculation omits any reference to the magnetic permeability of the core. The force between two electromagnets will certainly depend upon the identity of the core. If the core is air, the magnetic flux density will be small. Add soft iron or something of the sort and the magnetic flux density will be huge. I believe the F equation should us mu instead of mu_0, where mu is the magnetic permeability of the core. Am I missing something here? — Preceding unsigned comment added by 24.228.19.137 (talk) 20:16, 18 February 2013 (UTC)

In Eq. 4, the F equation, the permeability of the core is accounted for by the μ² in the numerator. It also has μ₀ in the denominator, as you noted, which makes it a little confusing. --Chetvorno^TALK 19:05, 9 April 2013 (UTC)

Depiction of magnetic field

Hello. In Electromagnet with gap.svg there are some field lines with begin and end, magnetic field lines form loops or extend infinitely in both directions, they don't form loops (Gauss's law for magnetism). I understand that the computation required to make an accurate representation of a magnetic field isn't trivial, but even not taking the image as an quantitative depiction of a magnetic field (Its description says than it isn't) this is an important conceptual flaw. QrTTf7fH (talk) 01:52, 31 July 2014 (UTC).

Hi, I drew that diagram. Are you talking about the leakage flux lines, labeled B_L, between the two vertical arms of the core? --Chetvorno^TALK 02:30, 31 July 2014 (UTC)

Thanks for your reply. Indeed those are the lines I'm talking about. QrTTf7fH (talk) 22:50, 4 August 2014 (UTC).

Well, I agree with you. I tried a couple of drawings to get the full leakage flux lines in, but they messed up the drawing so much that I did them this way. You have to remember that this drawing is designed to illustrate the text's "constant B field" approximation, used to analyze modern magnetic circuits in which the leakage flux is insignificant, so the B flux is assumed constant throughout the core. The number of leakage flux lines is exaggerated in this picture. Putting in those full leakage flux lines made it look like the density of B field lines varied around the core loop, and I thought that would be confusing for readers trying to understand the equations. Most of the field lines in the image do form closed loops, and I thought it would be clear from context that the incomplete ones did too. --Chetvorno^TALK 00:56, 5 August 2014 (UTC)

The term "ferromagnetic" in the introduction

About the recent changes. I feel an important point to make in the introduction for nontechnical readers is that the magnetic-core electromagnet is a ferromagnetic device; the necessary quality in the core is that it be ferromagnetic or ferrimagnetic. The theory behind the iron-core electromagnet, and thus all its incredibly important applications in modern society; motors, generators, transformers, and magnetic storage, is ferromagnetism. It should be mentioned in the intro. It's important to get it straight because there are several other types of magnetism in physics, paramagnetism and diamagnetism, which can confuse newbies. It's not enough to say the magnet is called a ferromagnetic-core electromagnet, it should be stated the core must be ferromagnetic. --Chetvorno^TALK 23:34, 15 September 2014 (UTC)

Chetvorno: Free feel to restore your edit, but I'd encourage you to avoid redundancy within a single paragraph. In my opinion, that needs to be fixed and that's why I undid it. Maybe I have made a mistake by undoing it outright rather than just pointing this problem. I don't object to make clear the role of ferromagnetism. Also take into account air core electromagnets. There may exist the convention to call those those not electromagnets, but only coils even though the principle of operation is almost the same. I don't know what's the predominant convention. Regards and thanks for contributing. QrTTf7fH (talk) 01:09, 16 September 2014 (UTC).

I believe air-core electromagnets are usually called solenoids, as the introduction says, although I have no objection to the term "air-core electromagnet" if you want to add it. If by redundancy you mean using the term "ferromagnetic-core electromagnet" in addition to the previous references to ferromagnetism, the latter is just making sure readers know the commonly used technical terms for electromagnets. Cheers, Chetvorno^TALK 01:40, 16 September 2014 (UTC)

A solenoid is a particular shape of electromagnet; air-cored electromagnets need not be solenoids.GliderMaven (talk) 02:24, 16 September 2014 (UTC)

Actually, that the core is ferromagnetic or ferrimagnetic is not sufficient (and I'm not sure off-hand whether it's necessary either, but I can't think of a counterexample). A magnetic core, suitable for an electromagnet for good performance really does have to be soft. There's plenty of ferromagnetic or ferrimagnetic materials that are very hard, and they are hardly ever acceptable for use as cores, as they perform virtually no better than air cores.GliderMaven (talk) 02:24, 16 September 2014 (UTC)

I understand that. I have no problem with also saying that the core must be a soft ferromagnetic material, but the most important property is that it is ferromagnetic or ferrimagnetic. Only ferromagnetic or ferrimagnetic materials have the high permeability required for all the important applications of electromagnets: motors, generators, etc. This is important basic science for the general reader. Here are some citations that electromagnet cores are ferromagnetic: 1, 2, 3, 4, 5, 6, p.4, 7 --Chetvorno^TALK 08:26, 16 September 2014 (UTC)

Why don't you just write magnetically soft ferromagnetic or ferrimagnetic material? That would solve the problem, wouldn't it? YohanN7 (talk) 09:32, 16 September 2014 (UTC)

That would be fine with me. --Chetvorno^TALK 11:46, 16 September 2014 (UTC)

It's still pretty rubbish. The point of the article is to try to explain how electromagnets work mainly for people who don't know. Simply stating that such and such a material is used isn't very good at all. You're much better off mentioning the typical requirements for a magnetic core material (high saturation and low susceptibility, only not necessarily using those words without defining them) and then giving a common example (iron). We have an entire article on magnetic cores anyway which can go into much more detail.GliderMaven (talk) 14:00, 16 September 2014 (UTC)

And I would question the usage of the term 'ferromagnetic material' unless you also define it first, 99% of the time, if you know what it means then you don't need to read the article anyway.GliderMaven (talk) 14:00, 16 September 2014 (UTC)

If the ancillary properties "saturation" and "susceptibility" are important for people to know, isn't the basic property "ferromagnetism" more important, without which the core will not work at all? You can't increase the field of an electromagnet (measurably) by inserting a core of wood. On the issue of defining ferromagnetism, the second section takes care of that. They can also click on the link to the article. Other examples of ferromagnetic core materials, such as ferrite could be mentioned.

I'm surprised there is any controversy about this. Other articles on ferromagnetic devices like Permanent magnet mention ferromagnetism up front. Ferro- (or ferri-) magnetism is the defining property of electromagnet cores. If I were an educator, that's one of the main points I'd want general readers to take away from the introduction. --Chetvorno^TALK 18:07, 16 September 2014 (UTC)

I don't think that's right. We're not just trying to create an article consisting of random facts. Why isn't wood any good? If we do it your way, the reader wouldn't know, it's not bad simply because it's not ferromagnetic.

Suppose a new material was created tomorrow using material science, magnetinium that works in a new way. Could you use it for a magnetic core for an electromagnet or not? According to what you want to write, you couldn't, solely because it's neither ferromagnetic nor ferrimagnetic. Are all ferromagnetic materials good for electromagnets? No, they're not. Hard ferromagnetic materials are useless. But not all ferromagnetic soft materials are necessarily very good either. If they have low saturation or poor permeability they're not very good in most case. And ferromagnetic materials vary very widely. In fact, most alloys are going to be pretty useless, even if technically ferromagnetic. Also other properties like conductivity are very bad. Ferromagnetic materials often have high conductivity; you usually don't really want that either.

We want the reader to understand which materials are likely to be good, irrespective of whether they're ferromagnetic or not, the underlying cause of the magnetism is nothing much to do with it.GliderMaven (talk) 20:04, 16 September 2014 (UTC)

You don't believe that the magnetic core in an electromagnet must be ferromagnetic or ferrimagnetic to increase the permeability? --Chetvorno^TALK 22:02, 16 September 2014 (UTC)

That's roughly correct.GliderMaven (talk) 23:06, 16 September 2014 (UTC)

Look at the references I gave above. Here are some more: 8, 9, 10. --Chetvorno^TALK 05:45, 17 September 2014 (UTC)

From a purely WP:LEAD point of view, the article has several sections devoted to cores and the requirement for ferromagnetism is stated prominently. It is a reasonable summary to have the ferromagnetic core requirement in the lead. The argument that not all ferromagnetic materials make good cores is irrelevant to the statement that all cores must be ferromagnetic. This is the logical fallacy of denying the antecedent; all A are B is not invalidated because some B are not A. That some new material for cores might be discovered that is not ferromagnetic is WP:CRYSTAL and also irrelevant, certainly not encyclopaedia worthy. I am not convinced that there are any genuine electromagnet applications of air-cored solenoids. The solenoid in its actuator role has a metal armature which is effectively acting as a core. SpinningSpark 09:52, 17 September 2014 (UTC)

If only what you said was true, I would have let it go, but not only are not all ferromagnetic materials suitable, but not only ferromagnetic materials are successfully used; specifically, ferrites are used for high frequency electromagnets, and are not ferromagnetic.GliderMaven (talk) 13:38, 17 September 2014 (UTC)

So it is not correct to state, or imply that only ferromagnetic cores can be used, which is what Chetvorno has been consistently doing.GliderMaven (talk) 13:45, 17 September 2014 (UTC)

No, if you will look at my statements to you above, I included ferrimagnetic materials:

"the necessary quality in the core is that it be ferromagnetic or ferrimagnetic."

"Ferro- (or ferri-) magnetism is the defining property of electromagnet cores."

"Only ferromagnetic or ferrimagnetic materials have the high permeability required..."

The wording of the introduction which I am supporting and you objected to and changed said "Much stronger magnetic fields can be produced if a "magnetic core" of a ferromagnetic (or ferrimagnetic) material, such as iron, is placed inside the coil" --Chetvorno^TALK 14:28, 17 September 2014 (UTC)

Since with Spinningspark, YohanN7, QrTTf7fH, and lastly GliderMaven's above statements it looks like there is consensus on the use of the terms "ferromagnetic" and "ferrimagnetic" in the intro, I restored the compromise wording suggested by YohanN7 above and added supporting citations. --Chetvorno^TALK 16:10, 20 September 2014 (UTC)

I think the reason for this misunderstanding is that the term "magnetic materials" is usually used for core materials in engineering texts and sources, to avoid having to write "ferromagnetic and ferrimagnetic materials" all the time. So the terms "ferromagnetic" and "ferrimagnetic" don't appear much. --Chetvorno^TALK 16:31, 20 September 2014 (UTC)

I still don't agree, but the bigger problem is that you are essentially trying to put a spin into the article that magnetic cores are the most important thing about electromagnets and that cores are ferromagnetic and hence ferromagnetism is the most important thing.

The problem with that is, try telling that to someone who has cancer and needs an MRI machine!!! Cores are not useful at high flux levels. The idea that air cored electromagnets don't matter, is a value judgement you're trying to impose on the article, and is unequivocally incorrect. Commonality and importance are NOT the same thing!

By doing that, you're distorting the article, very many features of electromagnets are common to both magnetic and non magnetic cores, but by trying to write the article in either-or terms that becomes almost impossible to deal with.GliderMaven (talk) 13:33, 22 September 2014 (UTC)

OK, I see the problem. Back in 2010 an anonymous broke lots of things and removed the introduction section. Rather than revert it, it was fixed up, which left the magnetic core section stranded. The problem with moving material into the lead is that it's not really repeated elsewhere, you're not supposed to only cover material in the lead, the lead is supposed to be a summary of the article not do the work for the article in describing how electromagnets are constructed.GliderMaven (talk) 14:53, 22 September 2014 (UTC)

Thanks GliderMaven! Does it look ok now? Is the lead as informative as we all would like? Gryllida (talk) 04:05, 23 September 2014 (UTC)

I think as discussed above the introduction needs to indicate what the magnetic core is made of, that it must be ferromagnetic (or ferrimagnetic). This is the defining property of the iron-core electromagnet and an important basic science take-away for general readers. All of the 10 references given above introduce the electromagnet as a ferromagnetic device. As SpinningSpark noted above, most of the article is devoted to analyzing the ferromagnetic-core electromagnet, so from WP:LEAD the introduction should mention the term. It was originally in the introduction, but User:GliderMaven edited it to remove the term. --Chetvorno^TALK 11:09, 23 September 2014 (UTC)

"I don't object to make clear the role of ferromagnetism." from QrTTf7fH above suggests that we can add it. Please go ahead and do so, and see if you can put it in a way which doesn't clutter the lead. Gryllida (talk) 11:35, 23 September 2014 (UTC)

GliderMaven has again removed the term "ferromagnetic" from the introduction. This is the defining property of an electromagnet core, and the consensus reached above is that due to its prominence in the article (most of the physics section is devoted to analyzing ferromagnetic core electromagnets) it should be in the introduction per WP:LEAD. --Chetvorno^TALK 21:44, 25 July 2015 (UTC)

Thanks, GliderMaven. --Chetvorno^TALK 22:16, 25 July 2015 (UTC)

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Electro magnet

What is a device that change the direction of the current in an electro magnet 196.188.112.67 (talk) 18:16, 28 March 2022 (UTC)

It's a current source. This section will be deleted, as it does not discuss content of the article. For any questions, please go to a forum. --Geek3 (talk) 19:22, 28 March 2022 (UTC)