Talk:Magnet

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Would Wikipedia consider a listing for a speculative field such as Magnetic Motors?

See: http://www.pureenergysystems.com/os/MagneticMotors/

The above question was part of the the exploration by a user who came and left in December 2003 of what Wikipedia isn't, and he seems to be part of a consensus that the answer is "no". --Jerzy 05:50, 2003 Dec 19 (UTC)

The article (Magnet) says

The end of a freely suspended magnet that starts to point towards the Earth's geographical North Pole, is by definition the magnetic south pole.

And no, i'm not about to point out that the geomagnetic field repeatedly reverses.

It's an even more pedantic issue than that, but i think i recall that what gets labelled N by convention is a north-seeking pole rather than a north pole, from which it follows that the geomagnetic pole in the northern hemisphere is a south pole. Maybe my instructor got befuddled in trying to talk about red end of the compass needle not being a north pole, but the consequences of being wrong about this are so small that 90% of confident sources could be wrong and never realize it. Does someone have a super-reliable source on this? --Jerzy 05:50, 2003 Dec 19 (UTC)

I just checked this out myself using the following procedure:
  1. I set up a small electromagnet (wire around a bolt).
  2. I connected a 9 volt battery to the wires.
  3. Using the right-hand rule (as defined on wikipedia), I set my hand on the coil such that my fingers were pointed in the from-positive-to-negative-direction.
  4. My thumb indicated which side was north (and then I labeled both sides with a sharpie).
  5. Then I set a stack of neodymium magnets near the magnet, and let them orient themselves on the table.
  6. I labeled the side of the magnets that faced the south side of the electromagnet as north.
  7. Then I suspended the magnets with a thread, and let them orient themselves.
  8. The north side of the magnets pointed toward geographic north, which means that the geographic north is actually a magnetic south pole.
  9. To make sure that the string wasn't twisted (or that something else wasn't forcing the magnets to move), I did everything I could to spin the magnets the other way. I twisted the thread in both directions, I moved the magnets to the middle of a room to account for any interactions with things in the room, and then I tried to point the magnets in the wrong direction. They always re-oriented themselves such that their north pole pointed toward the geographic north.

--Pkeck 15:10, 2005 Jan 14 (EST)

I did a similar experiment, but constructed a coil on a piece of wood with a aa battery. The N end of the coil, determinde by the right hand rule, pointed north when the wood was floated on water. Edison 22:30, 15 November 2006 (UTC)

Contents

[edit] Revamping this page

I started to rework this page with the hopes of making it much clearer and more organized. I feel that magnets are one of those topics that the average person might be interested in, so the content here shouldn't be too in depth. If they want more information, that's what the links are there for. If anyone sees anything that isn't clear or feels that something is missing, please help out. --Pkeck 11:21, 2004 Jan 14 (EST)

[edit] New Section on "Explaining Magnetic Attraction"

I'm curious about this new section. First (and most importantly), is this really an accurate way to describe what's going on in a magnet? I've never heard of or thought about it this way...which isn't to say that it's wrong, I've just never heard about it. Can you point to a page with more explanation of this idea of net current flowing around the surface of the magnet? I understand exactly what you mean, I just haven't ever heard of it.

Second, is it really easier to understand why magnets attract or repel one another through this explanation? I'm thinking that if you told the average person to imagine a cylinder of current carrying loops that all had current flowing perpendicular to the long axis of the cylinder and all in the same direction...and then to imagine how the current of adjacent loops negates the flow of current in their neighbors because they are flowing in opposite directions at adjacent points...which means that there will only be a net flow around the surface of the cylinder...I'm thinking the average person would be completely lost.

To be honest, it seems much more complex than simply saying that each atom is a dipole, which makes the whole magnet a dipole, and when opposite poles are near one another, there is attraction (and vice versa). To sum up: is this explanation correct? And is this explanation really more simple? Pkeck 21:11, 17 Feb 2005 (UTC)

Fully agree a new Section on "Explaining Magnetic Attraction" is needed. For instance I came to this article to understand why a)iron is atracted by a magnet and b) why a magnet is attracted by another magnet, and I came empty handed (unless I missed it) Manuel

[edit] Permanent magnets

I'd want to know, in these permanent magnets, is the magnetic field constant, or will it drain when used? And if so, will it regenerate? Take the average ABC hanging on your fridge. Will they come down due to weakened magnetic properties? Naturally one would assume that eventually they should come down, due to energy transformation. But I have yet to see a magnet fall down/stop beeing magnetic. So basically, is there any info on energy in permanent magnets?

A magnet does not lose energy by being used, and will stay on your fridge forever unless something happens (such as heating, shock or a strong external magnetic field) to demagnetise it. There is no "energy transformation", as you put it. The magnet is not using any energy ("doing work") to stay stuck to the fridge, because work = force x distance moved, and nothing is moving. The only energy transfer occurs when you stick the magnet to your fridge in the first place. As the two objects approach, some of the magnet's field goes into the metal of the fridge, resulting in a decrease in the field's energy (technically speaking, you are decreasing the reluctance of the magnetic circuit). The energy released from the magnetic field goes into pulling on your arm muscles, which turn it into heat. If you pull the magnet off the fridge, your muscles have to put that same amount of energy back into the field. You can do this as many times as you like without draining the magnet, because the energy is coming from you, not from the magnet.
There is some energy stored in the magnetic field of a permanent magnet, equal to the energy that was put in to magnetise it in the first place. This PDF is a good reference on the subject. This other PDF is good at explaining how permanent magnets work. Both of them discuss how to calculate the energy stored. --Heron 19:53, 27 July 2005 (UTC)

[edit] Iron filings

Do iron filings actually show the lines of magnetic force of a magnet, or do they just show how iron filings line up when they disturb the magnetic field of a magnet? --Light current 10:26, 21 September 2005 (UTC)

The former. Give it a try yourself. Salsb 11:45, 21 September 2005 (UTC)

Post copied from magnetic field

Field lines are just diagrammatic. The number drawn in any given diagram is arbitrary, the field is smooth, not ridged. Lines are just one way to show the direction and magnitude of a vector field at every point on a plane. Iron filings tend to mimic the shape of diagrammatic field lines, because adjacent lines of iron filings tend to repel each other, and because grains that are in contact tend to line up end-to-end with unlike poles touching. -- Tim Starling 12:32, Jun 24, 2005 (UTC)

But the average permeability in the plane of the paper has been increased cf that of air. So this will distort the field?--Light current 14:52, 21 September 2005 (UTC)

No one really understands the mysterious energy permanently stored in magnets. Most explanations are only theory based. So don't feel scared that mankind doesn't know how something works.

We're here to explain things, not to ascribe mystical qualities to phenomena!--Light current 23:45, 12 July 2006 (UTC)

[edit] Units of force

What's the point of having the units of force in the introduction? The attraction or repulsion is already indicated, and the units are irrelevant. Salsb 12:56, 21 September 2005 (UTC)

[edit] Calculating the magnetic force

between two magnet. it is not clear what μ ("mu") means, in the formula, and how to calculate this. if anyone can explain, and expand this subject. that would be great. thanks.


[edit] Section to be aded

You guys need a history section. There is no mention of magnets and their history on WP. hmmm.--Zereshk 09:58, 23 October 2005 (UTC)

[edit] My 4yo son wants to know 'How do they make magnets'?

So guys, how do they make magnets? Im assuming he's interested in the garden variety, solid stick things to your fridge variety. Thanks for any simple explainations..

Do you want to know how to take raw materials (like a ceramic powder) and turn them into a bar and then magnetize it, or do you just want to know how to take a material that isn't normally a magnet (like scissors) and then give it its own magnetic field? For a four year old, I'd go with the latter, the explanation is simpler and is probably what he's trying to ask. You can do an experiment with him (actually, you'll need to do it with him for safety) to turn something into a magnet: Buy a neodymium magnet (also known as a rare earth magnet). They're available from loads of online retailers and from some stores. Take the magnet and stick it to the metal part of the scissors close to the handle. Be very careful when you do this--rare earth magnets are extremely strong. Do not let your child play with them. Once you've got it stuck to the scissors, then have your son help you slide the magnet all the way down the scissors and all the way off. Then reattach the magnet close to the handle, have your son help you slide it off, and repeat this over and over. After like 20 or so slides down the magnet, you can use the scissors to pick up a single staple or something small like that.
An easy explanation could go something like this: Imagine you're running a comb through hair. As you run the comb through more and more times, all of the hairs get more and more lined up with each other, until all of the hairs are pointing in the same direction. You have to run the comb through the hair, and then take the comb out and go back to where you started, and then run it through again. In the scissors, there are lots of really tiny magnets all pointing in different directions. When you drag the big magnet along the length of the scissors, you're dragging all of the little magnets inside the scissors into rows. After a while, they're all pointed in the same direction (just like the hairs with the comb), so you've made all of the little magnets behave like one big magnet!Pkeck 05:28, 3 January 2006 (UTC)
Yes, that's a valid demonstration, but it's not really "how they make magnets". Unfortunately, the real process is not something you can easily do in your kitchen. Fridge magnets and the like are made from powdered ceramic material which is either sintered (welded by applying high pressure) into a rigid block, or embedded in flexible plastic. At this point, the object is not yet a magnet. It is then heated above its Curie temperature, placed inside the magnetic field of a much larger magnet, and cooled. When it is cold, it retains the magnetic field of the larger magnet. This is the adult version. I don't know what sort of words a four-year old boy understands, so I leave the translation up to you! --Heron 11:00, 18 February 2006 (UTC)

[edit] Far field of a magnet

The bit that says

At long distances, magnetic fields obey an inverse square law.

is incorrect. An electromagnetic wave will usually decrease by inverse square. So will the magnetic field of an isolated current element. An ordinary 'bar magnet', however, is usually modelled as a 'dipole element' in the far field (distances large compared with the separation of the poles). It becomes equivalent to an 'elemental current loop' whose far field is known to decrease with 1/ x³ -

http://www.netdenizen.com/emagnet/solenoids/ilooponaxis.htm

RAClarke 20:33, 9 January 2006 (UTC)

[edit] Calculating the magnetic force

Has anybody checked this "law" against a really reliable source like J. D. Jackson : " Classical Electrodynamics " , 3rd ed., (John Wiley & Sons, New York, 1998). I mean, I have studied physics now for quite a while and I never came across such a law.--LN2 02:43, 18 February 2006 (UTC)

I Love Magnets

LN2: With the units given it is definitely wrong. The general form is OK, and it could be made correct depending on how you quantitatively define "magnetic pole. For an alternate form of the law see

http://geophysics.ou.edu/solid_earth/notes/mag_basic/mag_basic.html

which seems to work out correctly.

In the form given, the numerator is Weber^2 = Tesla^2 x m^4. The denominator is (Tesla X m/Amp) X (m^2), so the result is Tesla x Amp x meter. Since a Tesla is a Volt-second, the result is Volt x Amp x second x meter = Watt x second x meter = Joule x meter which is definitely not a correct unit for force.

If no one disputes this I'm going to edit the main article in a week or so, to the form given in the link.

hfoltz, 18 March 2006

I agree: your version works out dimensionally, and mine doesn't, so mine must be wrong. It's interesting that both our references are from geophysics.ou.edu: mine from this page and yours from this one. It was unfortunate that I picked the wrong one. By the way, I reckon that since dipole moment is in A.m2 [1] and is pole strength times distance, then pole strength must be in A.m. --Heron 14:04, 19 March 2006 (UTC)

Heron: I agree on the units of pole strength: A-m. That agrees with engineering texts such as Kraus. The geophysics.ou.edu website is interesting, from the format it's clear that the two pages were written by the same person. Again, I think it has to do with the unit system and either form could be correct. It's unfortunate that we've reached the 21st century and magnetic field units and terms still haven't been completely standardized. Hfoltz


[edit] Magnetising current (a la transformer)

Should we have a para on this here --- or not? --Light current 23:32, 3 April 2006 (UTC)

[edit] Geomagnetic Reversal

I previously requested a source on this, as I had simply never heard of it before, and the wording "it is known" seemed to beg citation. DMacks did an excellent job of providing a timely response, however, now I have a new concern. The article Geomagnetic reversal states that the last occurance was approximately 780,000 years ago. However, as there are multiple different consensii on the age of the earth (see Dating creation), some of which hold that the planet is under 10,000 years old, I felt the simplest solution would be to simply change "it is known" to "it is believed". I think this wording will avoid any controversy between parties who hold the different viewpoints. Any thoughts? Dansiman 05:42, 14 April 2006 (UTC)

There are multiple religious viewpoints about the age of the earth. However, the scientific consensus is clear: the earth is about 4.55 billion years old. IMO, a scientific article doesn't need to weaken itself to account for religious opinions, and especially those that aren't about the topic at hand (if there were religious opinions about geomagnetic reversal itself, that could be relevant here). Young-earth creationism is relevant to age-of-the-earth discussions, but doesn't need to be brought up every time someone mentions something that is "older that that".
I agree that "it is known" sounds strange (the whole point of Wikipedia is to write what is known). OTOH, I think "it is believed" isn't much better. Better to avoid weasel words altogether. To the best scientific understanding and evidence at this time, geomagnetic reversal has occurred, and we provide a link to a discussion of that evidence. If someone wanted to debate how to write about that evidence, the page about that evidence is the place to do it. DMacks 06:53, 14 April 2006 (UTC)
New edit by Heron looks good. Dansiman 05:46, 17 April 2006 (UTC)

[edit] add a section

I suggest add a section that explains what would happen if we break a magnet into pieces Rockvee 05:31, 3 May 2006 (UTC)

Check out the third paragraph here: http://en.wikipedia.org/wiki/Magnet#Permanent_magnets_and_dipoles Pkeck 19:39, 12 June 2006 (UTC)

[edit] history

I'd like to see a section on the history of magnets, I went to this article for that reason but there was no such section yet --213.118.83.229 08:53, 22 July 2006 (UTC)

[edit] Geographic vs Magnetic Poles

Geographic North and South are the terms given to the points on the earth's surface through which the axis of the earths rotation pass, ie points at 90 degrees lattitude, points furthest from the equator, the "top" and "bottom" of the world. The magnatic poles are some distance from these and drift about somewhat. Navigators have to correct for this, particularly when near the poles. The section on geographic vs magnetic poles that points out (rightly) that the north (magnetic) pole is actually a south pole uses the term "geographic pole" in a way different to this. A way I've never come across before--Mongreilf 20:24, 24 August 2006 (UTC)

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