Magnet Myths and Misconceptions

[tinman]

  If the figure eight idea is correct then there should be a big increase in flux density close to the dipole center.  It should manifest as two peaks of opposing polarity.YesYesYesYesYes, moving from N-S the flux density through the sensor will first exhibit a peak that is opposing magnetic polarity from near the north pole on the same side of the magnet, and then moving a little closer to the south pole it should exhibit a second peak in the same magnetic polarity as near the north pole on the same side of the magnet.No.  Near the ends of the magnet where there is lots of curl, there will be substantial flux, and therefore flux density that is perpendicular to the dipole axis and registered by the senosr.  The sensor should read just as the diagrams I posted indicate.  Near the middle of the magnet where all the flux lines become parallel the perpendicular flux, and therefore flux density is zero.  A plot of the sensor output will be a non-linear, but monotonic line moving along from one end of the magnet to the other.

What a lot of crap Mark.Are you now telling TK how to run this test so as it shows your uniform field from one end to another?.
Quote:- If the figure eight idea is correct then there should be a big increase in flux density close to the dipole center.
Bullshit. There should be a decrease as the two opposite fields cancel each other out.

Quote:- A plot of the sensor output will be a non-linear, but monotonic line moving along from one end of the magnet to the other.
And why would it be non-linear if this field is suppose to be parallel to the dipole.

If this parallel field dose not change from one end to the other of the dipole,then neither should the readings from the hall sensor. If there is a change as i am saying,then the hall sensor will pick up that change near the center of the dipole.

@TK
I have said nothing in support of this bloch wall crap,and i am fully aware that a bloch wall dose NOT exist at the center of the dipole. If we face two north fields together from two magnet's,and place a steel bar between those two apposing fields,then you will have what might represent a bloch wall,as the domains now are facing opposite directions-are not aligned.

[tinman]

@TinselKoala,

You're straight out of a tale from Charles Dickens you miserly thread ball Scrooge! Get a job!

Bad form psycho-i mean synchro.
You have no idea of TK's position, so how the hell can you make a stupid statement like that.

[MileHigh]

A stack of disk magnets would be perfectly acceptable.  Heck, even a single cylinder magnet that makes nice flush contact with a long iron rod would be a pretty good substitute for the real thing.

Or perhaps on second thought, a long iron rod with mating cylindrical magnets on each end.  The art of cheating.  lol

[synchro1]

Dimensions: 1/2" x 1/4" x 1" thick
Tolerances: ±0.004" x ±0.004" x ±0.004"
Material: NdFeB, Grade N42
Plating/Coating: Ni-Cu-Ni (Nickel)
Magnetization Direction: Thru Thickness
Weight: 0.54 oz. (15.4 g)
Pull Force, Case 1: 10.54 lbs
Pull Force, Case 2: 10.54 lbs
Surface Field: 6474 Gauss
Max Operating Temp: 176ºF (80ºC)
Brmax: 13,200 Gauss
BHmax: 42 MGOe

The B84X0 is what many people commonly refer to as a "bar" magnet, as it is magnetized through the 1" dimension.  The poles are located on the smallest ends, so they behave like the old fashioned alnico bar magnets that have been used in school demonstrations. 


Price: $4.05

Shipping costs for this 1/2 oz magnet may put poor TK in dire straits!

[tinman]

Here is a really simple experiment. Lets just take a reed switch,LED and a 2.5 volt power source.Hook all in series,and then run the reed switch along the length of the magnet. If the LED stays on,then there is a magnetic field,if it go's out near the center of the dipole,then there is no magnetic field.

How dose a reed switch work-Quote wikipedia- The reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by W. B. Ellwood. It consists of a pair of contacts on ferrous metal reeds in a hermetically sealed glass envelope. The contacts may be normally open, closing when a magnetic field is present,