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General Science => General Science => Topic started by: dwright on 14/05/2019 20:40:48

Title: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 14/05/2019 20:40:48
Bar magnets side by side with opposite polarity will attract and attach to one another if they get close enough to one another. Besides that strong attractive force between the poles, is there also a weaker repulsive force between the sides of the magnets? The magnetic flux of the magnets flows in opposite direction along the sides, and there is a "null point" in the overall field.

(https://i.imgur.com/05NOL5W.png)
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 15/05/2019 06:44:41
Besides that strong attractive force between the poles, is there also a weaker repulsive force between the sides of the magnets?
No, what you see is an area reduced field which is zero in the exact centre - the null point.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 15/05/2019 18:44:58
No, what you see is an area reduced field which is zero in the exact centre - the null point.
The same pattern, reduced field, between bar magnets with like ends facing one another, is associated with repulsion, and that magnetic field cancels out or "bends" changing direction. It seems like, to avoid contradiction, there should be weak repulsive force when similar "collision" happens between two bar magnets side by side, even if net total is attractive force.

(https://i.imgur.com/br3pjSs.jpg)
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: pensador on 15/05/2019 19:45:21
The magnetic fields cancel at the null point.

You can view the magnetic flux like a current and the magnetic field as a voltage in an electric circuit.

If the voltage across a resistor is 0 ie equal at both ends of the resistor no current flows. The same applies in a magnetic circuit. If the magnetic field is 0 across a magnetic circuit no flux flows.

Nice graphics by the way
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 15/05/2019 20:39:34
The magnetic fields cancel at the null point.
The fields cancel also when two bar magnets have like poles towards one another, there is repulsive force then. It seems like if the fields cancels (it also looks like the field lines bend as well) from opposite flux direction there should be repulsion.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 15/05/2019 22:48:48
The fields cancel also when two bar magnets have like poles towards one another, there is repulsive force then.
They donít actually cancel. If you look carefully you will see that the lines of force are very tightly together and move out to the side. Itís not a null, although in some drawn diagrams it might look as though it is.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 15/05/2019 22:56:20
They donít actually cancel. If you look carefully you will see that the lines of force are very tightly together and move out to the side.
Yes that is what I said.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 16/05/2019 07:22:08
They donít actually cancel. If you look carefully you will see that the lines of force are very tightly together and move out to the side.
Yes that is what I said.

No, this is what you said:
The fields cancel also when two bar magnets have like poles towards one another, there is repulsive force then. It seems like if the fields cancels (it also looks like the field lines bend as well) from opposite flux direction there should be repulsion.

In reply #2 you posted diagrams. The top 2 depict iron filings and below some drawn field lines.
The field lines are misleading, in reality there are an infinite number of these lines closer to those shown in the filings diagrams. If you follow these lines in the centre you will see that there are always lines that connect the 2 magnets and although they are often at angles they always have a perpendicular component pulling the 2 together. If you look at the filings picture you will see that the null point is in fact infinitesimally small.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 17/05/2019 19:12:50
No, this is what you said

That was in reply to "The magnetic fields cancel at the null point", I replied "it also looks like the field lines bend as well". The overall question is if they "bend" both when magnets have like poles facing one another, and in the middle of two bar magnets with opposite polarity side by side, is there a vector of repulsive force (weaker than total vector of attractive force) for the magnets side by side?
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 18/05/2019 08:38:33
Is there a vector of repulsive force (weaker than total vector of attractive force) for the magnets side by side?
And the answer is no for the reasons I gave, all the vectors have attraction components perpendicular to the magnets.

Iíve added this because there is a possible misunderstanding:

The fields cancel also when two bar magnets have like poles towards one another, there is repulsive force then. It seems like if the fields cancels (it also looks like the field lines bend as well) from opposite flux direction there should be repulsion.
Cancellation of fields doesnít indicate repulsion, just no net field.
One of the problems with trying to interpret field lines in this way is that they donít specifically show repulsion. The lines just show how a test magnet at that point would align itself, in more sophisticated diagrams it would also show the magnitude of the force on that test magnet ie field strength. At a true null point that test magnet feels no force.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 22/05/2019 13:03:45
the answer is no

some potential evidence to prove that the answer is yes: if you look at magnets side by side, oriented with same polarity, you see a vector of repulsion along the diagonal, between the like poles, while there is attraction side-ways. Is this observation correct, and, does it imply there is repulsion as the question posited?

(https://i.imgur.com/9M4tmKZ.png)

(https://i.imgur.com/BlR20m5.gif)

(https://i.imgur.com/vgbwAnL.jpg)

(https://i.imgur.com/2030QbE.jpg)
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 22/05/2019 15:32:25
Not easy to see what you are looking at here, can you describe the exact set up and how you are observing the centre of the bars?
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 22/05/2019 15:43:45
Not easy to see what you are looking at here, can you describe the exact set up and how you are observing the centre of the bars?

It's two magnets side by side under a ferrocell, cylinder magnets but it would look the same with bar magnets. Ferrocells are an evolution of the ferrofluid concept, a very thin layer of oil with nano-size iron particles, allows you to see magnetic fields with a higher resolution. The repulsion that you can see is along the diagonal, between the like poles, compare the angle to the image at the bottom that shows standard two magnets with like ends facing one another, the angle of the repulsive vector in the two magnets side-by-side is 45į to the angle in the image at the bottom.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 23/05/2019 09:10:06
Ferrocells .........allows you to see magnetic fields with a higher resolution.
Ferrocells donít show the magnetic field lines. Even their inventor doesnít really know what they show; he describes the lines as lowest potential, but some lines are perpendicular to the field lines which would make them equipotential lines. Neither field lines nor equipotential lines show vectors of repulsion. Their inventor also describes the lines as diffraction patterns.
You also have to bear in mind that the field is 3 dimensional, but a ferrocell is only giving you a 2D slice at the location of the cell, itís not working like a telescope. If you want to see what is happening between the magnets as in your OP then the cell needs to be placed there to see what is happening. However, itís still not going to show repulsion.
The best way to determine the field at any location is to map out the field of two magnets individually, then overlay the 2 fields and perform a vector addition on the fields. If you do this you will see there is no repulsion at the centre area of the magnets.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 24/05/2019 22:00:06
You see repulsion along diagonal (between like poles) with iron filings as well, just happens to be higher resolution with nano-size iron particles.

(https://i.ibb.co/NF4FHZS/37-EE00-DC-B860-43-F5-A123-CAD736-DCA08-B.jpg)
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 24/05/2019 23:19:10
You see repulsion along diagonal (between like poles) with iron filings as well, just happens to be higher resolution with nano-size iron particles.
If you look carefully you will see that they are lines of attraction curving between unlike poles, the like poles are further apart so their influence is weaker than the closer unlike poles. I recommend you take measurements with a gauss meter.
Remember, the Ferrocell does not show lines of force. To quote the inventor ďThe lines we see using a cell can best be described as least potential and not field lines like iron filingsĒ.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 25/05/2019 12:06:11
If you look carefully you will see that they are lines of attraction curving between unlike poles, the like poles are further apart so their influence is weaker than the closer unlike poles.

Yes of course there is attraction between the unlike poles. The question is if there is also a (weaker) vector of repulsion along diagonal between like poles, as you see when viewing magnetic field both with iron filings and nano-size iron particles.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: pensador on 25/05/2019 13:44:09
I wonder if you made the magnet smaller would you change your mind. Perhaps not! but magnets don't com any smaller than one atom. https://spectrum.ieee.org/nanoclast/semiconductors/nanotechnology/single-atom-serves-as-worlds-smallest-magnet-and-data-storage-device.


You might consider an electron which has a magnetic field, would this change your mind.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 25/05/2019 23:26:59
would you change your mind.

Iím simply asking if the evidence of a vector of repulsion along diagonal, seen in the magnetic field both when viewed with iron filings and nano-size iron particles in a ferrocell, exists because there is a vector of (weak) repulsion where the magnetic field shows that.

(https://i.ibb.co/NF4FHZS/37-EE00-DC-B860-43-F5-A123-CAD736-DCA08-B.jpg)

(https://i.imgur.com/9M4tmKZ.png)

(https://i.imgur.com/vgbwAnL.jpg)
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 26/05/2019 00:17:40
Yes of course there is attraction between the unlike poles. The question is if there is also a (weaker) vector of repulsion along diagonal between like poles, as you see when viewing magnetic field both with iron filings and nano-size iron particles.
But you donít see it. You misunderstand what the field lines show.
They show the effect at any point on the orientation of a test magnet - usually a very small compass. We know from experiment that the field lines resulting from 2 magnets is the vector sum of the individual magnetic fields. You canít draw conclusions about attraction or repulsion between the magnets from the lines or null areas.
Consider another type of field, that between 2 masses. We can map out the field using a 1kg test mass and measure the force vector on that test mass. If you have 2 masses M1 and M2 of equal size then exactly midway between them the test mass will experience zero force - a null point, but that tells you nothing about the attraction between M1 and M2.
Measurements with a Gauss meter show there is no nett repulsion in the diagonals you mention.

I wonder if you made the magnet smaller would you change your mind. Perhaps not! but magnets don't com any smaller than one atom.
It doesnít matter what size a single magnet is, the topic here is the combined field of 2 magnets.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: dwright on 26/05/2019 02:13:40
But you donít see it. You misunderstand what the field lines show. [...] You canít draw conclusions about attraction or repulsion between the magnets from the lines or null areas.

From the poles as well. As you see with both iron filings and nano-size iron particles in ferrocell, repulsive vector between like poles along diagonal is at 45˚ to magnets with like poles facing one another. That can be reproduced by moving two magnets facing one another up and down respectively, to mirror 45į angle in magnets side-by-side.
Title: Re: Bar magnets side by side, opposite polarity, repulsion at null point?
Post by: Colin2B on 26/05/2019 08:26:42
As you see with both iron filings and nano-size iron particles in ferrocell, repulsive vector between like poles along diagonal is at 45˚ to magnets with like poles facing one another. That can be reproduced by moving two magnets facing one another up and down respectively, to mirror 45į angle in magnets side-by-side.
You are repeatedly ignoring the fact that neither the iron filings nor the ferrocell show repulsive vectors - read what the inventor says.
I suggest you find a probe Gauss meter and do some actual measurement. PM me when youíve done that and weíll continue this topic