Magnetic field rotation or not?

[zoobyshoe]

TurtleMeister wrote: "This setup cannot duplicate the experiments that I referenced in post #22 because the magnet cannot rotate by itself. With this setup the ring commutator always rotates with the magnet."

So remove the disc, the left-hand part of the magnet, and the slip ring joints. The field where the disc used to be is now nonuniform but that doesn't matter. The circuit is now from one pole of the meter, along the rotation and field axis to the bent wire bit where the disc used to be, and out through the field lines back to the other pole of the meter.

If you're talking about my drawing, there is no disk in it anywhere.

 

[Voltage Drop]

I don't know whether this will help, but I found it to be a useful way of looking at a Faraday Homopolar machine when the disk and magnet are moving together.

For reasons unclear to me, there appears to still be discussion as to whether the magnet field rotates with the magnet when the disc rotates.

To remove this possibility in this scenario, do not use a disc magnet but a simple small magnet.

https://www.physicsforums.com/threads/faradays-paradox.763966/page-2

 

[zoobyshoe]

I don't know whether this will help, but I found it to be a useful way of looking at a Faraday Homopolar machine when the disk and magnet are moving together.

For reasons unclear to me, there appears to still be discussion as to whether the magnet field rotates with the magnet when the disc rotates.

To remove this possibility in this scenario, do not use a disc magnet but a simple small magnet.

https://www.physicsforums.com/threads/faradays-paradox.763966/page-2

Just to be clear, let me paraphrase your explanation.

It sound like you're saying that when the disk and magnet rotate together, the leads connecting the center and edge of the disk to the meter remain stationary in the lab frame, creating a situation where there is relative motion between the magnetic field and at least one of the leads. The magnetic field, therefore, cuts this lead and generates a current that is detected by the meter.

The second scenario you describe is where the magnet and disk are held stationary in the lab frame, but the leads and meter are rotated around the magnet. Here again, the magnetic field "cuts" the leads and generates a current that can be read at the meter.

Did I understand your post correctly?

 

[Voltage Drop]

Perfect! You explained it far better than I.

 

[TurtleMeister]

@VoltageDrop
It seems like what you are describing is not a true homopolar generator (simple small magnet?). The type of generator used to demonstrate the Faraday paradox is designed in such a way that cancellation prevents the magnet from inducing current in the lead wires. There is a very good demo for this on YouTube. The demo allows the magnet, disc, and commutator to rotate independently. Just go to YouTube and search for Faraday paradox.

 

[zoobyshoe]

Perfect! You explained it far better than I.

Great. That same explanation for the current in that set up was offered here a few years ago by a guy who claimed a friend of his had figured it out. So, I'm familiar with it and it makes perfect sense in explaining the results Faraday got that baffled him. Faraday did not publish this experiment during his lifetime. People learned of it when his notes or "diary" was published in 1932. I've seen photocopies of those pages and it's clear it doesn't occur to him that the 'return' flux out in the space around the magnet might be what's generating the current in one of the lead wires.

@VoltageDrop
It seems like what you are describing is not a true homopolar generator (simple small magnet?). The type of generator used to demonstrate the Faraday paradox is designed in such a way that cancellation prevents the magnet from inducing current in the lead wires. There is a very good demo for this on YouTube. The demo allows the magnet, disc, and commutator to rotate independently. Just go to YouTube and search for Faraday paradox.

A "homopolar" generator is just another term for "unipolar" generator. All it means is one pole of the magnet is used. It's the Faraday motor run as a generator. The Faraday motor utilizes only one pole of the magnet. So, any generator that uses only one pole to generate the current is a "true" homopolar generator. If by "simple small magnet" all you mean is a short disk magnet ( as opposed to a long cylinder) you can still have a "homopolar" generator.

If one lead goes to the center of the disk and the other to the edge, I don't see how you can arrange any ultimate cancellation. The asymmetry is built into the way you have to take the current from the disk.

 

[Salvador]

the video some of you have been probably referring to.

 

[zoobyshoe]

the video some of you have been probably referring to.

Thanks for posting that.

The results are certainly mysterious.

One thing I'd like to check is whether the magnet is a conventional ferro-ceramic speaker magnet. It looks like it is. This would mean there's a large hole through the center that the viewer can't see in this video and that would mean there's flux taking a north-south path through this hole. That would complicate things.

 

[zoobyshoe]

OK, I think I see the problem: when the magnet rotates alone, the lead and disk system become a stationary loop that gets "cut" twice by the same field lines, creating opposing voltages. The "noise" is the result of the fact the EMF generated in the disk is somewhat stronger than that generated in the lead, where the field lines are more attenuated, so the opposing EMF's don't completely cancel each other. To see this, just forget it's a disk and mentally replace the connection between the leads with a short length of wire.

 

[Voltage Drop]

@VoltageDrop
It seems like what you are describing is not a true homopolar generator (simple small magnet?). The type of generator used to demonstrate the Faraday paradox is designed in such a way that cancellation prevents the magnet from inducing current in the lead wires. There is a very good demo for this on YouTube. The demo allows the magnet, disc, and commutator to rotate independently. Just go to YouTube and search for Faraday paradox.

In order for current to flow in a homopolar machine tat least 2 conditions must be met.

1. There must be a closed conducting loop that could be closed not only by a conventional load but by a measuring device such as an oscilloscope.

2. For a voltage to be generated that will cause current to flow there must be asymmetry in the movement of the flux cutting the loop so that one portion of the loop is exposed to a greater portion of flux motion than another.

Regarding the video, in case number 1 where the disk rotates and the magnet is stationary, the flux lines are cutting the moving conductor of the disk, the voltage is generated across the disk.

In case number 2 where the disk and magnet are rotating together, there is no voltage generated across the disk because there is no motion relative to it and the flux. There is, however, asymmetrical motion of the flux relative to the leads connected to the oscilloscope and the disk and a voltage is developed across the oscilloscope leads.

In case number 3 where only the magnet rotates and the disk is stationary, any voltage generated across the disk is canceled by opposing voltages generated in the oscilloscope leads, because there is no asymmetrical flux motion in the loop.

I've never been able to understand why this is a paradox.

 

[Circlotron]

What is needed is a setup with no external flux to influence the measurement wires, as per the picture. Preferably the pole piece would cover the entire top surface of the upper magnet and bottom surface of the lower magnet. Then hold the disc and wires stationary and rotate the magnets and pole piece as a unit as far as the pole piece allows and see what you get.

Picture Copyright 1997 by Don Lancaster and Synergetics.

 

[Voltage Drop]

Clever setup, but I see a problem.

If the disk alone is rotated, there will be voltage generated across the disk.

Because of the external return flux path on one side of the disk, the flux density across the disk will not be the same at all points on the disk and there will be significant eddy currents generated because of the different induced voltages across the disk. The detected output voltage will likely be that caused primarily by the lower flux density of the unshielded portion of the magnet which is within the loop.

When the disk and magnet are rotated together as much as possible, there will be no voltage generated across the disk and no eddy currents. Only the return flux of the unshielded portion of the magnet will be cutting the load wires and the same voltage will be induced in the load wires as was generated when the disk alone was rotating.

Instead of using disk shaped magnets think of using multiple small magnets of which only some (those outside the loop) are magnetically connected by a separate magnetic flux return path. When the magnets and disk are rotated together, only the uncovered magnets within the loop would have any effect on the generated voltage in the load wires and their flux return path can never be shunted by a separate magnetic return path.

Your drawing has made me curious, however, about what would happen if individual magnets were used with an external return path outside the loop as shown below.

What would the output voltage waveform look like when:

1 The disk alone was rotated and the magnets were within the loop.

2. The disk alone was rotated and the magnets were repositioned under the external flux return path.

3. The disk and magnets were both rotated together.

 

[Circlotron]

Because of the external return flux path on one side of the disk, the flux density across the disk will not be the same at all points on the disk

It's not my drawing so it's only approximately what I was talking about. The flux return path should cover the entire outer magnet faces. I don't see that the vertical section being on only one side of the disc would matter because the flux is entirely inside the vertical section. Also the flux strength is constant so there is no electric field radiating out from the return path. That is to say, if you wound several turns of wire around the vertical section like in a transformer core and secondary winding, nothing would be induced into the wire as far as I can see.

 

[Voltage Drop]

I don't disagree. My point was trying to demonstrate that if the flux return path was asymmetrical there would be a different flux densities through the disk under the return path and under the open part.

That would mean that there would be different voltages generated across the disk when the disk alone rotated.

The problem is that there can't be different voltages across the disk because each portion of the disk is electrically connected. This means that there will be large eddy currents generated within the disk basically putting the higher voltage in parallel with the lower voltage.

For this reason I think it would be difficult to determine what the actual output voltage would be when the disk alone is rotating in order to compare it with the output voltage when the disk and magnet are both rotating.

When the magnet and disk are both rotating, it matters only how much return flux cuts the load wires and I agree that this configuration appears to redirect most (but not all) of the return flux.

The topic of this thread is whether the magnetic field rotates with the disk magnet.

Instead of using disk magnets doesn't just using one small button magnet and then increasing the number of magnets so that they cover the disk demonstrate that the field does rotate?

 

[zoobyshoe]

Instead of using disk magnets doesn't just using one small button magnet and then increasing the number of magnets so that they cover the disk demonstrate that the field does rotate?

A physical arrangement of small enough magnets with their fields all oriented in the same direction will have a field that is indistinguishable from that of a larger monocoque magnet. In fact, a monocoque magnet is usually conceived of as a conglomeration of individual atomic magnets whose fields are all in the same orientation. Those who claim the field doesn't rotate seem not to realize this. Or, if they do, seem to think an individual atomic magnet can release it's field to be taken up by a nearby atomic magnet, or some such. While they don't seem to be denying the atoms of the magnet can be relocated in space by rotation, they somehow conceive of the magnetic field of those atoms as being able to detach from the atoms and stay where they are, due to inertia I suppose, when an attempt to rotate them is made. In other words, the magnetic field of an atom is misunderstood to be a separate entity from the atom.

Covering a disk with a large number of small button magnets with their poles all oriented in the same direction might serve as a macroscopic illustration of what's going on at the atomic scale, making it easier to grasp that each little magnet carries it's field with it when relocated.

 

[Voltage Drop]

I originally dropped into this thread after stumbling upon it while clearing out some old email.

In January 2005 I had sent an email to Mark Tomion who had a significant presence on the Internet regarding homopolar and Over Unity machines and was the designer of the StarDrive device.

http://web.archive.org/web/20071013103015/www.stardrivedevice.com/

I thought that for historical interest some might enjoy reading my email to him which is shown below in normal text and his response in bold font. I will restrain myself from making any further comments.Pretend that you the viewer are seated on top of the magnets on the rotor of a Faraday Homopolar Generator. What do you see ?
You see stationary magnetic flux lines extending vertically above you.
Correct. I see we're talking about the statorless variant, and that you are writing from the bottom of my Over-Unity page. As you might have read in the Statorless Generator Analysis section, I have objectively assessed but pretty much dismissed that configuration as being fundamentally less efficient than the traditional induction dynamo variant (having a stator).

When the rotor is rotating, the flux lines are still stationary relative to you.
Not correct: believe it or not, as mentioned in the Over-Unity page's 'Introduction' section, the flux lines produced by a permanent magnet do NOT rotate with the motion of the magnet itself! To wit, no voltage will be generated by rotating the permanent magnets in the 'stator' relative to a stationary conductive disk 'rotor'. This has never been satisfactorily explained in classical theory, to this day, but it's so.

If you look over your head while the rotor is turning, however, would you not see the wire connected to the load passing through this magnetic field once per revolution ?
On the basis of the above, no.

Would not these conductors obey Lenz's law and would there not be a voltage generated in them ?
Sorry, same answer!

 

[TurtleMeister]

Here is an illustration of a very simple homopolar motor. It consists of only three parts; a battery, magnet, and a loop of stiff wire. The magnet is attached to the negative terminal at the bottom of the battery. The wire lays on top of the positive terminal at the top of the battery. The wire ends touch the outer rim of the magnet at the bottom forming a commutator. It can be operated in two ways. 1) The battery and magnet are held stationary while the wire spins around them. 2) The wire is held stationary while the magnet, or the magnet and the battery spin. Videos of both these methods can be found on YouTube.

If the magnetic field were separate from the magnet (field does not spin with the magnet) then there would be a problem. The wires could be permanently attached to the battery and the magnet and the entire unit as a whole would spin about it's stationary field. Notice that you will not find a video of the motor operating in this fashion. Probably because it won't work. If it did, then there would be a torque without a reaction torque. And that would be a violation of Newton's third law. So I conclude that the field must rotate with the magnet.

 

[zoobyshoe]

Here is an illustration of a very simple homopolar motor. It consists of only three parts; a battery, magnet, and a loop of stiff wire. The magnet is attached to the negative terminal at the bottom of the battery. The wire lays on top of the positive terminal at the top of the battery. The wire ends touch the outer rim of the magnet at the bottom forming a commutator. It can be operated in two ways. 1) The battery and magnet are held stationary while the wire spins around them. 2) The wire is held stationary while the magnet, or the magnet and the battery spin. Videos of both these methods can be found on YouTube.

Just want to note that the magnet used cannot be a ferro-ceramic magnet because that material has exceptionally high electrical resistance. Most people use rare Earth magnets which conduct very well (and are, incidentally, very much stronger).

If the magnetic field were separate from the magnet (field does not spin with the magnet) then there would be a problem. The wires could be permanently attached to the battery and the magnet and the entire unit as a whole would spin about it's stationary field. Notice that you will not find a video of the motor operating in this fashion. Probably because it won't work. If it did, then there would be a torque without a reaction torque. And that would be a violation of Newton's third law. So I conclude that the field must rotate with the magnet.

This sounds right to me. However, no one may have tried it because no one may have thought of it. Personally I would test the idea by suspending the whole from a thread to eliminate friction.

I would warn anyone thinking of trying this (permanently attaching the wires to the battery) to put some resistance in the circuit because I have heard that shorting one end of a battery to the other with no load can make the battery heat up and explode. When these motors are in operation with the rotor spinning they are always breaking contact - you can see a little spark where the wire touches the magnet - which I think prevents the overheating of the battery. Or maybe use really thin wire that will burn out like a fuse if the current gets too high. Anyway, take precautions not to get hurt. Put a sheet of plexiglass between you and the motor.