Magnet Myths and Misconceptions

[tinman]

You are referring to the field outside the magnet, correct?

If so, then that is not a correct statement. The field at the center (and outside) of the dipole is parallel to the dipole and does not change direction. The flux density outside the magnet at the center is however weaker compared to the ends. But if you were able to insert your Hall probe into the middle of the magnet material at the center, you would find the flux density just as high, if not higher than what you might measure at either end of the magnet. Agreed?
So again, when you swipe a coil near either end of a magnet, you induce a strong voltage in the coil. When you swipe the same coil across the center of the same magnet, you induce little to no voltage in the coil. Is that because there is no field or flux at the center? No. It is because you are inducing just as much positive voltage as negative voltage, and the two cancel.

Yes indeed.

[tinman]

The confusion would seem to lie in the fact that in between the two planes of the poles the sensor shows a constant max value and polarity if the sensor face is pointing in the same direction as the poles N-S axis. However if sensor is always facing towards the magnet center we see two half spheres of different polarity.Another note, just above or below the side center region the hall sensor can be rotated 90 deg and the value and polarity do not change in any way, very strange.


This was unexpected and I will leave it with everyone here to make sense of it.


AC

You mean something like the picture i posted some time back?

[allcanadian]

@tinman

You mean something like the picture i posted some time back?

If we were to plot the "difference" between the center zero plane between the two poles and the looped conventional paths then yes I believe it very well may follow the line you have depicted. To be honest I never thought of that until I saw your diagram.


There are points where the parallel and perpendicular measures from the hall sensor appear equal within the field where the two planes intersect.


I should be able to add another sensor at 90 degrees and plot a second graph with labview. Then a third graph showing the difference between the two and follow the line.


AC

[tinman]

This takes the flux that formerly was surrounding the bar magnet and concentrates it in the region between the poles or pole pieces. It is the _same flux_ that formerly flowed along the sides of the magnet from pole to pole. The opposites attract just as they did in the straight magnet. The center region between the poles has just been moved out to the side, and instead of being spread around the body of the magnet it is now concentrated mostly to the area defined by the width of the poles or pole pieces. Just as when you hold a hose or water nozzle perfectly vertical, the water flows down all around the outside of the nozzle and would have a hard time driving a turbine wheel, but if you bend the nozzle over, now the water flows in a stream away from the hose body, making it easier to drive a water wheel. Nothing new has been introduced, the position of the flow (water) or magnetic flux (magnet) has just been relocated away from the magnet body to make it easier to use.  Now I think you are really grasping at straws.

Please refer to my "7 questions". This _fact_, which can be observed in my video, shows the same thing that a moving wire would show in the same position. Recall that current is induced in a wire that "cuts" across magnetic field lines. This means at the exact center region of the magnet, the wire would have to be moving radially towards and away from the body of the magnet to "cut" the field lines perpendicularly. This is kind of hard to arrange experimentally with actual straight magnets and wires, but the Hall sensor shows the same thing: see "hall effect" in your favorite reference to see how the Hall voltage is produced. Also it is demonstrated by 2-piece homopolar dynamos, where a strong current is produced by moving a conductor, at right angles to the flux, through the midpoint of the field between the poles of a U or C shaped magnet.

Simply by bending a bar magnet into a C-shape I have introduced NO new magnetic fields! I have simply redirected the flux so that instead of "flowing" along the long axis of the bar magnet from pole to pole,it is now flowing from pole to pole out in a space away from the body of the magnet.

A misunderstanding there TK,as you said-Quote: .But also of course you will be able to do work by spinning a coil of wire in the same position as your "forceless" probe or non-acting reed switch: See "electric motor" in  WIKI

The coil of wire produces magnetic fields !dose it not!?,there for you have introduced two more magnetic fields.

The Hall sensor test in my video definitely shows that there is a flux at the midpoint of the magnet, and since it is giving almost the same reading there as on the pole itself, it shows that the flux is going mostly straight through the plane of the sensor, which is held perpendicular to the long axis of the magnet

.

Yes,it shows flux in the center,but both the value of that flux and it's strength is 0.

[MarkE]

You mean something like the picture i posted some time back?

Your depiction is absolutely wrong.