Re: [Phys-L] magnetic field reversals

[Bernard Cleyet <bernard@cleyet.org>]

Lit. search made late:  


On 2015, Oct 05, , at 10:01, Carl Mungan <mungan@usna.edu> wrote:

> It seems somewhat common to find that bar magnets used in labs get their magnetization reversed, so the actual poles are opposite the ones painted on the bar. I am wondering why reversals are so common?
>
> If it’s because they get dropped or whatever, why isn’t it more common to find that the net magnetization vector shifts by some angle relative to the axis of the bar, rather than shifting around by 180 degrees? Aren’t the domains small compared to the physical dimensions of the bar (say 1 cm in diameter)?


Perhaps the mfr. is cheap (as in shoddy) by chosing a rather “soft”  material.  


http://www.pasco.com/prodCatalog/SE/SE-8637_magnetizer/  

Doubt if the above will magnetize a “good” hard bar, unless it includes the discharge of a large cap. with diode to prevent oscillation.  


bc, thinks the material is no better than dress makers needles that ambient field is sufficient.  


Wrong    Very strong field for high coercive materials:  7kG or 0.7T  (note: B not H)


http://www.electrotechnicproducts.com/content/Magnetizer%20Instructions.pdf