Magnet Myths and Misconceptions

[hartiberlin]

New topic for some members who want to contribute to this topic.

Regards, Stefan.

[TechStuf]

Great topic title. Much more titillating than, say....

"Come put on a show of personality conflicts, squabbling, bickering, and other reality show style drama to increase site traffic and keep the forum chugging along!"

Where there is conflict, hey, at least there's energy. 


TS

[poynt99]

I asked Stefan to create this topic because on this forum there is an underlying deficiency in basic knowledge about how magnets and electromagnets work.

Many people here are working with and measuring magnets and electromagnets and are misinterpreting the information they are gathering about them. In order to interpret that data correctly, you first need to have a good understanding of the fundamentals about magnetic fields. The aim of this thread will be to present the fundamentals and have an open forum discussion about them.

A number of myths and misconceptions will also be listed and an attempt made to properly address each as they are presented.

Here are a number of myths and misconceptions to start:

1. Conventional permanent magnets and coils/inductors (cored or not cored) inherently exhibit a Bloch wall as part of their existence, usually as either a dead or transition zone in the middle of the magnet or coil.

2. Permanent magnets exhibit a neutral zone in the middle where there is either a very weak or no field at all.

3. When I move my Hall probe around my magnet or coil, I see null zones in my readings as they go from +'ve to -'Ve on the scale, therefore this proves that there are Bloch walls and neutral zones in magnets and coils.

4. The field of a magnet is stronger at its "poles" compared to the field strength at the magnet's center.

5. The traditional depiction of a magnet with half of it shaded blue (north pole) and the other half shaded red (south pole) is an accurate representation of how a magnet really works and how the field lines run through and around it.

Points 1. - 5. above are all false and incorrect.

The first 4 myths and misconceptions could easily be cleared up if one were to first clear up myth number 5. But let's deal with the "Bloch wall" misunderstanding first.

First and foremost, Bloch walls can only exist inside ferromagnetic material, so that immediately eliminates air and copper.

Bloch walls CAN exist inside ferromagnetic materials such as iron and strontium ferrite (ceramic magnets) for example. They exist when inside the ferromagnetic material, there are adjacent magnetic domains that are oriented in different directions. This happens in an unmagnetized piece of iron for example (the domains are random), or when a contiguous piece of ferromagnetic material has purposely been magnetized in more than one direction in different sections of the material.

Note that Bloch walls typically do not exist inside the ferromagnetic core of a coil. The core is typically situated "inside" the coil winding, so the core's magnetic domains are all polarized in the same direction. See second picture of coil field orientation.

Let's now look at myth number 5.

This simplistic depiction of a magnet leads us to believe that there is no field (or that there is a "Bloch wall") right in the middle where the color changes from red to blue. It also makes us believe that there are two polarities of magnetism. This is simply incorrect. Magnets really should be illustrated with one solid color and a single arrow from one end to the other (See attachments and link to Hyperphysics). Why? Because this is actually how they work.

There is no discontinuity of field in the center of a magnet, or solenoid for that matter. A simple test if you have a Hall probe is to take two cylindrical magnets and stack them together. Insert the Hall probe between the two magnets right in the center and measure the field strength. Is it zero? Is it as strong if not stronger than what you measure at either end of the magnet?

I highly recommend this Hyperphysics page be studied until clearly understood.

[TechStuf]

You couldn't have started this topic yourself, Poynt99?

Just a head's up...

The archaic field model you have displayed fails even a 5th grade level examination.  One has only to bring two N poles and two S poles into close proximity to dispel the notion of quanta flow in one direction.  We are to believe, with as yet ZERO plausible explanation anywhere to be offered from the "halls of science" that two N poles brought to close proximity would not exhibit greater opposing force than two S poles brought to the same opposing positions?  What with all those "virtual photons" being ejected at relativistic speeds from only one end of a magnet, one should think that some appreciable differences could be observed!

Yet, what do we find upon close examination with simple tests?  Such a curious incongruity should have been properly explained long ago, one would imagine.  Yet, I have seen no published data that sufficiently accounts for such disrepancy. 

Try it yourself, bring two S poles into contact with one another.  Once contact is made and opposition force is retained, the doorway to the old thinking is slammed shut.  How does one compare the data obtained with the results one finds from flipping the magnets and doing the same with the N poles?

Even simply levitating two ring magnets on a pencil N to N and S to S disproves the old field model.

I have done tests on numerous occasions and find the old field model to be incorrect for various reasons.


TS

[MileHigh]

TS:

That's called leading yourself down a garden path.  Your posting is hard to decipher but you seem to be implying that there will be a difference in force between a N-N opposition as compared to a S-S opposition.  That's not true.

Who said anything about "virtual photons being ejected at relativistic speeds?"  Who said anything about a "quanta flow in one direction?"  There is no flow of anything!  It's just more garden-pathing on your part.

You can see how problematic it can be for an experimenter to "half learn" something and then tack on the crazy myths and beliefs that you see on the forums.

You have it set in your mind that "the field model is incorrect."  Then with this belief fixated in your mind, you do some experiments to "confirm" what you want to believe.  Hence the name of this thread, "Magnet Myths and Misconceptions."

Remember, there is no such thing as "North" and "South" so your discussion about differences between the two is moot.  Those are just artificial constructs that we have created to make it easier to talk about magnetic fields in practical applications.

The solution for you is to keep climbing up the learning curve and Poynt is a great communicator and teacher.  To do that effectively you have to get rid of that "garden pathing" crutch that is hampering you.