Magnet Myths and Misconceptions

[tinman]

   Anyone on here actually believe in particle physics and the research that's going on
at CERN? Or is it a load of crap?
               John.

I did say discrete partical physics dose not account for magnetic attraction-nothing to do with there non existance.

[tinman]

Two like poles repel for the same reason that two opposite poles attract:  The field seeks its lowest energy state.  Separating a pair of poles is analagous to pulling apart the two ends of an extension spring.  This is why all manner of magnetic devices work by reducing the magnetic path length from one pole to the other:  that reduces the energy.  Bringing two like poles together is analagous to pulling on two extension springs each anchored to an opposite wall as the other.

Well thats telling us what is happening,but not how it's happening. In fact,i would like anyone to show me a link that shows how magnetic fields attract and repell each other-what is the physical force that applies these two forces.

https://www.youtube.com/watch?v=evfUTmx0uh8

[ramset]

Tinsel
What size and kind of magnet do you need for this?
also other needs for this work??


thx
Chet

[TinselKoala]

@NoBull:
Thanks for your response. So you agree with the "rights" on all of the 6 hypotheses. But we still don't know if my stack of disks is "good enough" for the experiment. I'd still like to hear from some of the other participants in the discussion about all 7 questions before I proceed further.

@ramset:  Personally, I think that the stack of disks is fine to use instead of a bar magnet. I can make a weak bar magnet by magnetizing a piece of mild steel barstock, of course, but stronger is probably better for this kind of test. Buying a special magnet from, say, K&J Magnetics would be kind of silly, since the shipping cost alone will be quite a bit more than the cost of the magnet, and there would be several days of delay in getting it here. By next Friday the issue will probably be forgotten already.
http://www.kjmagnetics.com/proddetail.asp?prod=D4Y8

"Other needs for this work"... heh, that's a good one. Some confidence that proper conclusions will be drawn by "the usual suspects" given the observed data, would be nice. 
It all depends on "how fancy" one wants to get. I can spend a day or more programming an Arduino and Processing to display some nice graphs on a computer screen, or I can just show a video of the scanning process and the raw voltage output of the Hall sensor as it is scanned along the magnet. I prefer to do the latter, since it is so simple and, to my thinking, unequivocal in its results.

Allcanadian has already shown data from a similar experiment, with a fancy display and everything. I am not sure from his description about the exact orientation of the Hall sensor and some other important variables. His graphs would make more sense if the x-axis was given in position along the magnet rather than time, though.

[allcanadian]

@TK

1)Do we think that the community here will accept an experimental result obtained from a stack of disk magnets, instead of a solid bar magnet? If not, why not?

Already done it, not even comparable. I have the same problem you do and have every magnet under the sun except for a long bar magnet.

2)The Hall sensor of course will read its maximum value for a given field strength in a given location if the "field lines" are exactly perpendicular to the sensor surface. Right?

I think of it as a sensor loop, it measures the magnitude and polarity of the magnetic field within the loop. Try rotating the sensor in the field as you will see what I mean.

3)At the same location, an angled field, or equivalently an angled sensor, will give a lesser reading. Right?

Exactly and even a slight off angle makes a huge difference. It is actually very hard to keep the sensor stable when amplifying the signal.

4)In the "peanut waist" picture, the field lines are not parallel to the long axis of the magnet stack, but dip in at the waist or "Bloch wall"("arrow" pointing toward magnet body) and come back out again ("arrow" pointing away from magnet body) on the other side of the BW. In the conventional picture, the field lines are parallel to the long axis of the stack and there is no "dipping" in and out at a "Bloch Wall" waist or equator. Right?

I would agree the picture is incomplete and every time I fire up the sensor I generally learn something new.

5)So a Hall sensor held with its plane at right angles to the magnet's long axis, and scanned along the length of the magnet, would read very differently in the two cases. Right?

As it should I believe and a rotating sensor or 4 sensors at 90 deg to each other may be the answer but trying to plot this in 3D would be a nightmare.

6)If the "peanut waist" picture is true, the sensor being held at right angles and scanned along the magnet will experience a changing angle of the field as the field dips toward the "Bloch wall" waist, and then an also changing angle as the field dips up out of the equator on the other side. This will cause changing readings as the sensor is scanned past the "Bloch wall equator".  Right?

That's where a gyro/accelerometer would be awesome I think, I have a few on hand and have been throwing around code on how to plot a moving/rotating sensor .

7)But in the conventional case, with the field lines strictly parallel to the long axis except near the end poles, the sensor will experience the field lines straight through the plane of the sensor, and thus the sensor's reading will remain constant, and _at the maximum value_  as it is scanned along the magnet's long axis. Right?

That is exactly the issue I had and it was constant, the far field would appear constant however the near field not so much. I would think a change in sensor orientation would show an increasing/decreasing field strength dependent on the polarity at that point so long as the sensor rotates about it's own axis. As I said, even a small deviation from the sensor axis ie rotation changes the measure dramatically.


I'm kind of pumped your going to do this and I will be doing my thing on this end. Hopefully Sunday I can start on the gyro/accelerometer code but the processing is going to be the kicker. I'm not even sure how in the hell I'm going to plot this in 3D, lol.


AC