Sorry for the lack of postings lately... My wife and I are in Maryland helping our daughter with the arrival of a wonderful grand-daughter! she was born last week; some complications, but both doing fine now. We've been gone from my electronics bench for about a month already...
However, a short vid showing some budding scientists -- grandchildren! There should be a certain child-like curiosity and joy as we undertake experiments IMO! Showing that they are interested and setting up their OWN electronics bench LOL.
http://www.youtube.com/watch?v=itXT8H5EXoo&feature=youtu.be
I came across a very good vid, Michael Faraday, on PBS -- and it shows his homopolar motor at the end, the very first motor:
http://www.youtube.com/watch?v=yVDHKKTC4tA
I'm doing some research on Faraday's paradox again... based on the homopolar motor / generator. Consider the attached diagram and the following vid:
http://www.youtube.com/watch?v=zOdboRYf1hM&feature=fvwrel
First -- is the diagram correct for this vid? (ie, are the directions of the Lorentz qv X B forces correct?)
Second -- place the whole set-up on a freely-rotating wheel support (vertical axis) -- which way will the battery+magnet spin?
It's an interesting motor professor.
I see the magnetic field crossed the vertical side/plane of the loop......is this what makes the motor possible? hm....
Quote from: GibbsHelmholtz on 2012.04.08, 19:47:37
It's an interesting motor professor.
I see the magnetic field crossed the vertical side/plane of the loop......is this what makes the motor possible? hm....
In part yes -- there are forces which result in torques on the left (force away from you in the diagram, hence (x), like the feathers of an arrow going AWAY from you ) and on the right (force towards you in the diagram, hence (.) ). There are also forces on the wires at the bottom where the field is stronger, tending to cause rotation in the same sense -- convention calls this -z rotation (right-hand fingers in direction of the spin, thumb points downward, hence -z axis).
FYI, pls see http://en.wikipedia.org/wiki/Homopolar_motor where the diagram also comes from ;)
OK -- please pull your right-hand, apply the right-hand-rule (RHR) and check that the forces shown on the diagram are correct!
Direction of the force found from I x B, that is, fingers in direction of current I, rotate rt-hand-fingers to direction of magnetic field line B, then force F is in direction of thumb. Try it! (PS -- I find the diagram is correct.)
Note that instead of rotating the WIRE as shown above, we can hold the wire fixed and rotate the magnet -- see attached. Diagram gives the idea -- note battery "upside down" from photo. Obviously we can change the orientations of the magnet and the battery. We can also place the magnetic field EXTERNAL to the system; still works.
Actually, I did try the fingers and palm. lol It does indicates torques and correct direction.
I'm just interested in the diagram because it relates to the experiment we talk about in the other thread. There are actually field lines crossing the vertical planes, the higher it goes up, the more field lines it captures.
As for the motor, the concept seems different than a pulse motor. It uses charges in the conductor as torque while pulse motor use 2 magnetic fields attracting or repulsing.
Quote from: GibbsHelmholtz on 2012.04.08, 21:41:55
Actually, I did try the fingers and palm. lol It does indicates torques and correct direction.
I'm just interested in the diagram because it relates to the experiment we talk about in the other thread. There are actually field lines crossing the vertical planes, the higher it goes up, the more field lines it captures.
As for the motor, the concept seems different than a pulse motor. It uses charges in the conductor as torque while pulse motor use 2 magnetic fields attracting or repulsing.
Right - thanks.
Now the question before us:
Consider this set-up: http://www.youtube.com/watch?v=zOdboRYf1hM&feature=fvwrel
Next, place the whole set-up on a freely-rotating wheel support (vertical axis), wires not touching the support --
which way will the battery+magnet spin? -z (same as the wire) or +z ??
Quote from: PhysicsProf on 2012.04.08, 22:19:02
Right - thanks.
Now the question before us:
Consider this set-up: http://www.youtube.com/watch?v=zOdboRYf1hM&feature=fvwrel
Next, place the whole set-up on a freely-rotating wheel support (vertical axis), wires not touching the support -- which way will the battery+magnet spin? -z (same as the wire) or +z ??
I don't know but common sense would be the opposite direction. It's action reaction.
Quote from: GibbsHelmholtz on 2012.04.08, 22:37:26
I don't know but common sense would be the opposite direction. It's action reaction.
A good theoretical way to look at it -- apply Newton's Third Law, action-reaction. And you're right, this is what theory would predict.
But -- in this field, some are challenging Newton's 3rd law...
And it's not just a question of the batt+magnet spinning the opposite direction as the wire -- but,
are the torques EQUAL in magnitude (and opposite in direction)?
So, if we're not willing just to say we already know for SURE the torques are equal based on the Third Law,
HOW do we find out? that's the next question; I have some ideas but seeking input (and hope you're following along the argument).
Quote from: PhysicsProf on 2012.04.09, 00:01:06
A good theoretical way to look at it -- apply Newton's Third Law, action-reaction. And you're right, this is what theory would predict.
But -- in this field, some are challenging Newton's 3rd law...
And it's not just a question of the batt+magnet spinning the opposite direction as the wire -- but,
are the torques EQUAL in magnitude (and opposite in direction)?
So, if we're not willing just to say we already know for SURE the torques are equal based on the Third Law,
HOW do we find out? that's the next question; I have some ideas but seeking input (and hope you're following along the argument).
After giving this more thoughts.... I'm heading out to buy battery. lol
If you're saying you are going to do the experiment -- I agree that is the best way to find out. "Theory may guide, but experiments decide."
Out here, I need a few parts... will see what I can do also on this question. (And there are other -- somewhat related -- questions of interest as well with this puppy. The first electric motor, Faraday 1821. Revisited.)
PhysicsProf,
Take note that the magnet will not 'feel' a torque when you hold the wires still but the conductor it is attached to will - the screw.
The only time the magnet will feel a torque is when it is also the majority of the conductive loop. N3 doesn't apply to the magnet because the magnetic field is a property of space, not of the magnet.
I just read about Faraday paradox. Indeed it has something to do with action reaction. Conductor rotate in a magnetic field generate voltage but magnetic field rotates while conductor remains stationary does not generate voltage. Hm...
I suppose the same thing can be apply on a motor instead of generator.
1. A conductor move while magnet remains stationary generate voltage.
A current carrying conductor in a stationary magnetic field produce a force on the conductor.
2. A conductor and magnet rotate together generate voltage.
A current carrying conductor produce a force even when the magnet moves with it.
3. The magnet rotate while conductor stationary generate no voltage.
The magnet will not experience a force while the conductor carry current.
I will perform some experiments to see if these 3 things matches.
WW!
I just read your post. So it is true that the magnet would not feel the force! Wow....
Quote from: WaveWatcher on 2012.04.09, 03:20:44
PhysicsProf,
Take note that the magnet will not 'feel' a torque when you hold the wires still but the conductor it is attached to will - the screw.
The only time the magnet will feel a torque is when it is also the majority of the conductive loop. N3 doesn't apply to the magnet because the magnetic field is a property of space, not of the magnet.
Note that the magnet is covered with a conductive surface, so this surface-conductor completes the circuit. Current in THIS conductor on the magnet-surface generates a torque in the opposite direction from the torque on the wires; but I don't know if the magnitudes of the torques are EQUAL (hence the need for experiments -- thanks Gibbs).
Let me cut to the chase. Let's set the whole apparatus on a frictionless surface, or suspended from above (free to rotate) -- free to spin about the z-axis one direction or the other. Let's also AFIX the wires to the surface of the magnet, so there is no relative motion between wire and magnet -- they are constrained to rotate (or remain stationary - the starting condition) TOGETHER.
So now, what do you fellows predict -- will the system begin to rotate, or not?
I'm trying to see what you would predict, WW, in this case, and Gibbs. I'm going to go with Newton's 3rd = N3 on this; no rotation. Conservation of angular momentum likewise gives the null result.
But if experiment shows otherwise -- I will be delighted! and Faraday's paradox would then acquire new meaning perhaps...
I see what you mean professor. I've designed a setup where we can accomplish it more practically. Tell me if this satisfy the condition of your experiment.
The picture below shows a pair of magnet sandwiched a conductor in between. When we supply a current through the conductor, it would either remains stationary or deflects. If it doesn't deflects, then no momentum is violated. I think with this setup we can adjust the length to increase torque in case of sensitivity issue.
BTW, I say it will deflects. :)
Quote from: GibbsHelmholtz on 2012.04.09, 04:56:51
I see what you mean professor. I've designed a setup where we can accomplish it more practically. Tell me if this satisfy the condition of your experiment.
The picture below shows a pair of magnet sandwiched a conductor in between. When we supply a current through the conductor, it would either remains stationary or deflects. If it doesn't deflects, then no momentum is violated. I think with this setup we can adjust the length to increase torque in case of sensitivity issue.
BTW, I say it will deflects. :)
Actually, your proposed experiment is not the same -- there is no rotation, is there?
No, it needs to be a Faraday motor, and it needs to be mounted as a system, FREE to rotate or not, as noted as the crucial condition for the experiment proposed above.
Quote from: PhysicsProf on 2012.04.09, 11:29:56
Actually, your proposed experiment is not the same -- there is no rotation, is there?
No, it needs to be a Faraday motor, and it needs to be mounted as a system, FREE to rotate or not, as noted as the crucial condition for the experiment proposed above.
The conductor and magnet either rotate into or out of the page.
The point of this experiment is to see if the wire could carry the magnet while using the same magnetic field it carried. Is this a crucial point?
Quote from: GibbsHelmholtz on 2012.04.09, 11:47:17
The conductor and magnet either rotate into or out of the page.
The point of this experiment is to see if the wire could carry the magnet while using the same magnetic field it carried. Is this a crucial point?
I don' think there will be any movement there Gibbs. You've removed the relativity factor.
Quote from: poynt99 on 2012.04.09, 13:36:41
I don' think there will be any movement there Gibbs. You've removed the relativity factor.
You may be right. It is just my thought that magnet and conductor rotates together generate voltage, so why current can't rotate magnet and conductor affix. I'm not too familiar with relativity factor though.
Also as WW stated the magnet would not feel a force because the wire is pushing on space to propelled itself. So if the wire pushing on the magnet to propel, then there would be no movement, but if it pushes on space, then in theory it could carry the magnet.
Quote from: GibbsHelmholtz on 2012.04.09, 13:41:48
You may be right. It is just my thought that magnet and conductor rotates together generate voltage, so why current can't rotate magnet and conductor affix. I'm not too familiar with relativity factor though.
In your experimental setup, there is no relative movement between the B-field and the conductor. In the HG, there IS relative movement between the two.
That's what I mean by relativity factor. :D
By the way, there is no paradox at all. Conceptually, it's simple.
Quote from: poynt99 on 2012.04.09, 13:52:58
In your experimental setup, there is no relative movement between the B-field and the conductor. In the HG, there IS relative movement between the two.
That's what I mean by relativity factor. :D
By the way, there is no paradox at all. Conceptually, it's simple.
I see. Then can you explain the third thing in this experiment? There is no relative movement between the disc and B-field.
The experiment proceeds in three steps:
1. The magnet is held to prevent it from rotating, while the disc is spun on its axis. The result is that the galvanometer registers a direct current. The apparatus therefore acts as a generator, variously called the Faraday generator, the Faraday disc, or the homopolar (or unipolar) generator.
2. The disc is held stationary while the magnet is spun on its axis. The result is that the galvanometer registers no current.
3. The disc and magnet are spun together. The galvanometer registers a current, as it did in step 1.
http://en.wikipedia.org/wiki/Faraday_paradox
This may help explain, Gibbs -- an experiment involving two ring magnets, bottom one free to spin -- but it does not!
http://www.youtube.com/watch?v=IlUY3snoWI8
Note this question with the vid; any answer to this?
Quote""Replace the rotating magnet on the drill by a conducting disk that is shorted out from center to perimeter to form a closed circuit. Put a small bulb in this circuit to confirm there's current flow when rotating the drill above the magnet This is basically faraday's homopolar generator. But the thing I want to get at is showing what happens to the bottom magnet that can rotate freely. It should spin in the other direction. According to newton's third law..."question by Broli123"
Quote from: GibbsHelmholtz on 2012.04.09, 16:22:43
I see. Then can you explain the third thing in this experiment? There is no relative movement between the disc and B-field.
The experiment proceeds in three steps:
1. The magnet is held to prevent it from rotating, while the disc is spun on its axis. The result is that the galvanometer registers a direct current. The apparatus therefore acts as a generator, variously called the Faraday generator, the Faraday disc, or the homopolar (or unipolar) generator.
2. The disc is held stationary while the magnet is spun on its axis. The result is that the galvanometer registers no current.
3. The disc and magnet are spun together. The galvanometer registers a current, as it did in step 1.
http://en.wikipedia.org/wiki/Faraday_paradox
Yes, it's quite simple.
When you spin a magnet on its polar axis, there is absolutely no change in its magnetic field. From Shadowitz p.395:
QuoteThe lines of B are not defined with respect to the magnets but are defined with respect to a stationary observer, If B is absolutely uniform then turning of the magnets has absolutely no effect on the B at any point: B is independent of time. So there is no transformer induced voltage in this case.
Therefore in case 2., there is no relative motion between the conductor and the magnetic field.
And in case 3. when the disc and magnet are spun together, it is exactly the same scenario as case 1.
Steve, regarding your question when the magnet is replaced with a shorted disc:
What direction does the guy say the bottom magnet rotates?
To my thinking, it should rotate in the same direction as the rotating disc.
Quote from: poynt99 on 2012.04.09, 18:29:29
Yes, it's quite simple.
When you spin a magnet on its polar axis, there is absolutely no change in its magnetic field. From Shadowitz p.395:
Therefore in case 2., there is no relative motion between the conductor and the magnetic field.
And in case 3. when the disc and magnet are spun together, it is exactly the same scenario as case 1.
Poynt,
So in all 3 cases, the B field is stationary?
Quote from: GibbsHelmholtz on 2012.04.09, 19:06:58
Poynt,
So in all 3 cases, the B field is stationary?
A better way to think of it is that it is unchanging. Yes.
So back to the question. You didn't think there be movement in my setup and the reason is there is no relative movement between the conductor and the B field. The relative movement between those generate current. So if we apply a current, then the conductor would move relative to the B field. And of course, the B field is not affix to the magnet as we have discussed.
Quote from: PhysicsProf on 2012.04.09, 18:18:39
This may help explain, Gibbs -- an experiment involving two ring magnets, bottom one free to spin -- but it does not!
http://www.youtube.com/watch?v=IlUY3snoWI8
Note this question with the vid; any answer to this?
Professor,
I don't know if Broli did that experiment and saw the bottom magnet spin, but I think the bottom magnet won't spin regardless of there is current drawing or not.
The field IS affixed to the magnet. If you move the magnet in any direction, the B field moves with it. This is not the same things as spinning the magnet on its axis and seeing the the B field does not change.
So, in your experiment you apply a current to the wire, which runs across the B field. If the B field was held stationary, then the wire would deflect. Since the magnet (and hence B field) and wire are attached, I believe there will be no movement.
Simple test to do.
It does move!!!
Movement was detected. I just make a rectangular loop and tape a magnet on the bottom of the loop. The loop is being hung. Current is applied to the loop. The force is very small so I have to pulse it like a swing to see the movement build up.
Quote from: poynt99 on 2012.04.09, 18:37:57
Steve, regarding your question when the magnet is replaced with a shorted disc:
What direction does the guy say the bottom magnet rotates?
To my thinking, it should rotate in the same direction as the rotating disc.
Poynt, the guy's (broli123) question was:
Note this question with the vid; any answer to this?
QuoteQuote
""Replace the rotating magnet on the drill by a conducting disk that is shorted out from center to perimeter to form a closed circuit. Put a small bulb in this circuit to confirm there's current flow when rotating the drill above the magnet This is basically faraday's homopolar generator. But the thing I want to get at is showing what happens to the bottom magnet that can rotate freely. It should spin in the other direction. According to newton's third law..."question by Broli123"
So he predicts the bottom magnet will spin in the "other direction", you suggest " it should rotate in the same direction as the rotating disc" -- and I think it may spin in the same direction - or, the bottom magnet may not spin at all!
Looks like we need an experiment to resolve the question.
Quote from: GibbsHelmholtz on 2012.04.09, 20:19:11
It does move!!!
Movement was detected. I just make a rectangular loop and tape a magnet on the bottom of the loop. The loop is being hung. Current is applied to the loop. The force is very small so I have to pulse it like a swing to see the movement build up.
Yes, we expect that simple loop to move, as the magnetic field is quite independent as we saw also in the video.
Care to do the homopolar motor or generator experiments now? delineated above; won't repeat here.
Quote from: GibbsHelmholtz on 2012.04.09, 20:19:11
It does move!!!
Movement was detected. I just make a rectangular loop and tape a magnet on the bottom of the loop. The loop is being hung. Current is applied to the loop. The force is very small so I have to pulse it like a swing to see the movement build up.
To verify the movement is aided by the magnet, replace the magnet with an equivalent mass, and try again. Don't be surprised if it still moves.
Quote from: poynt99 on 2012.04.09, 21:40:12
Just to verify the movement is aided by the magnet, replace the magnet with an equivalent mass, and try again.
There's no need for that. I just used my hand to hold the magnet. I do feel a force. So there is action reaction, therefore, my setup cannot move. I also agree that the direction magnet should be the same of shorted disc.
What I found is that force on a current carrying wire in a B field is just attraction repulsion of a magnetic loop.
Quote from: GibbsHelmholtz on 2012.04.09, 22:10:37
There's no need for that. I just used my hand to hold the magnet. I do feel a force.
Actually you do need to do it if you want to be sure the magnet has anything to do with the result. The idea was to remove the magnet completely from the experiment, and try with just the wire and an equivalent weight.
Quote
What I found is that force on a current carrying wire in a B field is just attraction repulsion of a magnetic loop.
Not sure what you mean here.
Gibbs,
Poynt's description of the field position being dependent upon the magnet's position is quite correct. Any motion you detected may show that the amount of movement or even the ability to move may be relative to the experiment's orientation to the Earth's poles.
The wire should move, perhaps even better, with nothing attached.
I feel the need to elaborate ....
You can say the field is affixed to the magnet or not affixed. The reason is there is no viable explanation of what a magnetic field is, other than some vector math to calculate changes in some unknown variable based upon location relative to the magnet.
Can you say the wake of a speeding boat is affixed to the boat?
Can you say the light beam created by focusing light through a lens is affixed to the lens?
I suppose the wake could be defined as part of the speeding boat because it wouldn't be there unless the boat was moving relative to the water and we weren't able to see or feel the water unless indirectly by noticing the motions of another boat. If that was the case, we could just denounce the existence of water.
Also, focused light affixed to the lens used to create it? You could and probably would say the light was part of the lens if you didn't understand the nature of light or, at least, think you understood the nature of light.
It wasn't that long ago we thought magnetism could have no effect upon light and light no effect upon magnetism. Now, almost every computer hard drive on the planet uses the latter effect, and some, also the former.
We can say almost anything we wish about magnetism as we can't really define it well until we can see and feel the water directly (reference to speeding boat, again).
The stuff contained within the space calculated using vector math that is a magnetic field is not part of the magnet nor is it affixed to the magnet except when you consider it to be the result of the magnet and an unknown media, plane or some other factor.
Saying you feel the reaction force on a magnet is an easy to understand way of putting it but that raises more questions.
I suggest picking an understandable explanation of magnetism that works in all cases then sticking with it. That is my choice O0
Thanks men,
Yes, it is possible that the earth's magnetic field is involved. But even if the conductor is using the earth's magnetic field, it is still pushing on the earth and therefore taking the earth's momentum. I think I'm starting to understand what makes homopolar works. It is the relative motion between two bodies. I haven't have much luck in making a homopolar so i will concentrate on it. The concept may involve asymmetric capacitor, iron aether wind propulsion and more . lol
Gibbs,
For the homopolar motor and your moving wire... Lorentz explains both nicely.
Quote from: WaveWatcher on 2012.04.10, 02:54:13
Gibbs,
For the homopolar motor and your moving wire... Lorentz explains both nicely.
The Lorentz forces work out nicely, agreed... But not so sure about that angular momentum is conserved!
unless it somehow links to the earth's B field... but that I can restrict also I think (at home).
Tonight I completed two simple homopolar (HP) motors, both worked after a little playing with them. Late again here; will post a photo tomorrow.
Quote from: GibbsHelmholtz on 2012.04.09, 03:32:41
...
Conductor rotate in a magnetic field generate voltage but magnetic field rotates while conductor remains stationary does not generate voltage. Hm...
...
A magnetic field never rotates. No referential frame can be attached to a field. A magnetic field is just vectors giving B at points in space. They can dynamically change from location to location giving the illusion of a movement, as a light spot moving along a wall when nothing is really moving on the wall.
Moreover when a magnetic field source is rotating around its axis of magnetic symmetry, as a disk magnet about its axle, the field remains strictly identical to itself, i.e. the field remains the same in all space points, so the effect is the same as if the magnetic source was at rest. This is why there is no difference in the Faraday disk when the permanent magnet is rotating or at rest.
Now the question of relativity and reaction. The Lorentz magnetic force is:
F = q*VxB.
The most important point is that V is the charge speed relative to the observer, neither relative to the field source nor to the field (the latter being an absurdity). This point is generally not understood and the cause of the urban legend of the absence of reaction.
It means that the action/reaction applies between the observer and the charge, not between the charge and the field or the field source (the magnetic field acts just like a catalyst).
When this is understood, the functioning of the Faraday generator or motor becomes clear and without paradox.
For the case of the Faraday disk generator, we have a conductor disk rotating in a constant magnetic field which is perpendicular to the surface of the disk.
From the viewpoint of an observer at rest, e.g. linked to the sliding contacts connecting the axle to the rim of the disk, the electrons of the disk have a tangential linear speed V and so, the observer sees the electrons deviated by a radial Lorentz force which is not counterbalanced by the electrons of the sliding contacts at rest, therefore a current flows.
From the viewpoint of electrons on the disk, there is an electric field E=BxV which is the Lorentz transform of the magnetic field, thanks to the rules of Einstein's relativity. So the electrons feel an electric force F=q*E which is the same as the Lorentz force viewed by the observer at rest.
Now about the reaction:
From the viewpoint of our observer at rest, when a current flows, the electrons of the disk are seen going radially through the magnetic field. So the observer sees that a Lorentz force is acting on them transversally, which means here tangentially, opposing the mechanical force that rotates the disk.
From the viewpoint of the electrons on the disk, they are always submitted to an electric field E'=BxV' but now V' is the resultant speed of the electrons moving under the tangential mechanical force of the disk (as previously) AND the radial electric field. Therefore there is a restoring force opposing the mechanical force, which is the tangential component of F'=q*E'.
Thanks Exn,
It does makes sense. One question I have is the Faraday disk does not change polarity. The electric field E = BxV , V does change direction when we rotate it CW or CCW, that means E changes polarity?
I'll let exn or someone handle that, Gibbs -- we're on the road again!
Here's a shot of the small hp motor I completed before leaving; works just as well with an AA battery, and runs for a VERY long time (surprisingly stable). Neo magnet under the battery, plus one wire -- that's all!
Quote from: GibbsHelmholtz on 2012.04.10, 13:17:49
Thanks Exn,
It does makes sense. One question I have is the Faraday disk does not change polarity. The electric field E = BxV , V does change direction when we rotate it CW or CCW, that means E changes polarity?
Gibbs,
I'm wondering what you are seeing. The polarity of the induced voltage can be reversed by reversing either the excitation or the direction of rotation, not both. At least, in all of these I have constructed :o
Here is a test that may shed some light on things:
Well professor, If he doesn't you will have to be recommissioned as a teacher. lol
I'll try your set up. Don't have neo mag but I'll improvise.
----------------------------------------
WaveW,
I just read it off Wiki that the output voltage never changes polarity. I've been thinking about it all day long.
-------------------------------------------
Harvey,
Very nice point you made there. I've also thought of this too. My intuition said that only one of them work.
I made the professor's version. Keep wondering why it doesn't work, then found out the top is not abraded for conduction. lol I have to cover the magnet with aluminum foil.
Next to the picture is my design of some serious high power turbo homopolar. It sure is high power because I zapped it with 18V and it only move back and forth. lol Probably too heavy and unbalance.
Quote from: GibbsHelmholtz on 2012.04.10, 23:35:47
WaveW,
I just read it off Wiki that the output voltage never changes polarity. I've been thinking about it all day long.
I see. By the words 'does not change' it means the polarity doesn't require commutation or polarity reversal to make it rotate.
Quote from: WaveWatcher on 2012.04.11, 01:20:59
I see. By the words 'does not change' it means the polarity doesn't require commutation or polarity reversal to make it rotate.
Um... I mean this
----------
Description and operation
[edit] Disk-type generator
Basic Faraday disc generator
This device consists of a conducting flywheel rotating in a magnetic field with one electrical contact near the axis and the other near the periphery. It has been used for generating very high currents at low voltages in applications such as welding, electrolysis and railgun research. In pulsed energy applications, the angular momentum of the rotor is used to store energy over a long period and then release it in a short time.
In contrast to other types of generators, the output voltage never changes polarity. The charge separation results from the Lorentz force on the free charges in the disk. The motion is azimuthal and the field is axial, so the electromotive force is radial. The electrical contacts are usually made through a "brush" or slip ring, which results in large losses at the low voltages generated. Some of these losses can be reduced by using mercury or other easily liquified metal or alloy (gallium, NaK) as the "brush", to provide essentially uninterrupted electrical contact.
If the magnetic field is provided by a permanent magnet, the generator works regardless of whether the magnet is fixed to the stator or rotates with the disc. Before the discovery of the electron and the Lorentz force law, the phenomenon was inexplicable and was known as the Faraday paradox.
-----------
http://en.wikipedia.org/wiki/Homopolar_generators
Quote from: GibbsHelmholtz on 2012.04.10, 13:17:49
...
The electric field E = BxV , V does change direction when we rotate it CW or CCW, that means E changes polarity?
...
Hi Gibbs,
The polarity changes when the disk rotates CW or CCW. This is easily testable: you just need to rotate a conductor disk magnet with a driller while touching the center and the rim with the probes of a voltmeter.
It is what the equation says: E=BxV is a vectorial product, so if B
or V is reversed E is reversed, if B
and V are reversed, E remains the same.
It is a classical Faraday motor whose Harvey gave the schematics in the left view (no effect is to be expected for the right view):
(http://www.overunityresearch.com/index.php?action=dlattach;topic=1411.0;attach=7716;image)
Due to the electric field from the battery between the center of the disk magnet and the rim, there is a radial current in the neo. The electrons are crossing the magnetic field so the Lorentz force is tangential. The electrons transfer the Lorentz force applying on them to the lattice of the metal and make rotate the magnet which would accelerate indefinitely if there was no friction.
Under the effect of braking due to losses or if we try to extract a mechanical work or during the phase of angular acceleration, there is a reaction force from the disk lattice on the electrons. Therefore the electrons move not only radially under the effect of the voltage, but also partly tangentially due to the mechanical force from the rotating metal lattice in which they are embedded. It follows that the Lorentz force onto the electrons acquires a radial component that opposes the electric force provided by the battery, and so more current is needed to maintain the rotation. Action/reaction works perfectly.
Gibbs,
I see now which sentence is your reference.
This is a typical Wiki problem. The sentence was written referring to the commutation or it is written by one of those fools thinking a varying DC amplitude is an alternating polarity(AC). As long as the voltage doesn't cross zero (the reference point) it is still DC.
The first time I ran across the AC/DC argument was from a previously highly respected electrical engineer who declared that the applied transformer primary current was AC because the secondary output was AC. The transformer fried anyway ;D
(http://www.overunityresearch.com/index.php?action=dlattach;topic=1411.0;attach=7716;image)
Exn,
I'll do the experiment today to see if polarity change.
I've tried to analyzed the forces on Harvey's drawing. The red line indicates Lorentz force pushing the loop out of the page. However, notice that the blue force on the magnet section is pushing the magnet into the page. If we add the blue to the red, the forces exactly cancel out to zero!
qV x B , V is constant so we can use q X B
q is just proportional to the segment , there are more segments in red than blue
but, even if we make the loop larger, more segment would take in less magnetic field lines. Since field line is conservative
q(blue) x B = Q(red) x b
Therefore, the conclusion is... the net force is zero! no movement. ;)
Quote from: exnihiloest on 2012.04.11, 08:20:19
It is a classical Faraday motor whose Harvey gave the schematics in the left view (no effect is to be expected for the right view):
(http://www.overunityresearch.com/index.php?action=dlattach;topic=1411.0;attach=7716;image)
Due to the electric field from the battery between the center of the disk magnet and the rim, there is a radial current in the neo. The electrons are crossing the magnetic field so the Lorentz force is tangential. The electrons transfer the Lorentz force applying on them to the lattice of the metal and make rotate the magnet which would accelerate indefinitely if there was no friction.
Under the effect of braking due to losses or if we try to extract a mechanical work or during the phase of angular acceleration, there is a reaction force from the disk lattice on the electrons. Therefore the electrons move not only radially under the effect of the voltage, but also partly tangentially due to the mechanical force from the rotating metal lattice in which they are embedded. It follows that the Lorentz force onto the electrons acquires a radial component that opposes the electric force provided by the battery, and so more current is needed to maintain the rotation. Action/reaction works perfectly.
Juxtposing Harvey's clever figure (right) with the one I presented in my initial post #1, we see that there IS AN EFFECT, a force on the wire, for the one on the right (Harvey's Fig) , due to the Lorentz force on the current-carrying wire, arising from I x B.
Now let us consider this experiment (getting back to my questions regarding angular momentum conservation).
Let's support Harvey's RIGHT fig., say on a free-to-rotate disc -- again, with the wire connected (soldered, say) to the CENTER of the neo, and the other end of the wire connected to the CENTER of the battery. Then -- there is NO torque (r X F) on the battery+neo. BUT, there IS A TORQUE on the wire as I showed in my previous post.
Experimentally, I would like to see a time-switch in the wire, to close after a certain time so there is NO TOUCHING of the system when the switch closes; also I would add an LED so one can see when the switch closes and the current flows.
NOW -- will the entire system thus configured begin to rotate, or not? There is a torque on the wire, so it seems there should be rotation.
HOWEVER -- in that case, it also seems that angular momentum would NOT BE CONSERVED, for there is nothing counter-rotating. Hence, an important question arises about whether or not Angular Momentum is Conserved -- which question I have raised before.
Quote from: PhysicsProf on 2012.04.11, 13:13:25
Now let us consider this experiment (getting back to my questions regarding angular momentum conservation).
Let's support Harvey's RIGHT fig., say on a free-to-rotate disc -- again, with the wire connected (soldered, say) to the CENTER of the neo, and the other end of the wire connected to the CENTER of the battery. Then -- there is NO torque (r X F) on the battery+neo. BUT, there IS A TORQUE on the wire as I showed in my previous post.
Experimentally, I would like to see a time-switch in the wire, to close after a certain time so there is NO TOUCHING of the system when the switch closes; also I would add an LED so one can see when the switch closes and the current flows.
NOW -- will the entire system thus configured begin to rotate, or not? There is a torque on the wire, so it seems there should be rotation.
HOWEVER -- in that case, it also seems that angular momentum would NOT BE CONSERVED, for there is nothing counter-rotating. Hence, an important question arises about whether or not Angular Momentum is Conserved -- which question I have raised before.
Professor,
For Harvey's left picture:
1. Soldered - no rotation
2. not soldered - rotation
For Harvey's right picture:
1. Soldered - no rotation
2. not soldered - no rotation
There is a torque on right picture, but if you follow the wire, the bottom portion contain the opposite torque. Since negative and positive torque on the same wire. It can't move. However, I find it difficult to hang the whole thing without wobbling.
Quote from: GibbsHelmholtz on 2012.04.11, 13:36:22
Professor,
For Harvey's left picture:
1. Soldered - no rotation
2. not soldered - rotation
For Harvey's right picture:
1. Soldered - no rotation
2. not soldered - no rotation
There is a torque on right picture, but if you follow the wire, the bottom portion contain the opposite torque. Since negative and positive torque on the same wire. It can't move. However, I find it difficult to hang the whole thing without wobbling.
Yes, I also find there is an opposing force on the bottom portion as the B-field reverses direction over that portion. However, it is not clear whether the resulting torque EXACTLY CANCELS the force on the rest of the wire loop, so that the torques add to ZERO, OR NOT.
Also, one can place a magnet at the top also...
Travel time! Hope to be back here tomorrow morning.
Quote from: PhysicsProf on 2012.04.11, 13:58:54
Yes, I also find there is an opposing force on the bottom portion as the B-field reverses direction over that portion. However, it is not clear whether the resulting torque EXACTLY CANCELS the force on the rest of the wire loop, so that the torques add to ZERO, OR NOT.
Also, one can place a magnet at the top also...
Travel time! Hope to be back here tomorrow morning.
That is a good point professor. It could be zero, it could be not. I think the charges exert a force on the magnet, so if the magnet does not move in some other direction, momentum would be violated.
I've tried the Faraday disk experiment. I could not get a stable reliable voltage. I think it makes sense to say that polarity reverse because it is the same as the Hall effect. However, I think that even if the external magnetic field is not apply, as the disk rotates, the charges create its own magnetic field. Because this magnetic field due to mechanical rotation move with less than sound speed comepare to electron with light speed in magnets, the self generate B field is very small. I think this is the forces that keep electron orbits and not going into the nucleus . We cross the B field generate by electron and its speed and see the force pointing outward. If electron move in the other direction, its self generate B field also change direction, the cross product of B and V again point outward.
I've come up with a model for electromagnetic induction. This concept is based on Lorentz forces and charge movement.
The set up is we have a primary loop and a secondary loop. Let's walk through step 1-6:
1. Current is injects into primary loop. Test charge move as indicated by the arrow.
2. As the charge move circular around the loop, a B field is set up denotes by green dots going out of the page.
3. Lorentz force pushes the charge outside. We can see by V x B or using the right hand rule.
4. Now the charge resides more on the outside of the wire than the inside. This set up an electric field going outward denotes by the gray arrows.
5. The secondary loop charge experiences this E field and moves outward.
6. As it moves outward, it subjects Lorentz force cause by the B field due to primary current. Using the right hand rule, it pushes the charges in the opposite direction to the primary loop.
Interesting Homopolar Motor:
Superconducting DC Homopolar Motor (http://atg.ga.com/EM/defense/dc-motor/index.php)
8)
Quote from: Harvey on 2012.04.14, 00:14:45
Interesting Homopolar Motor:
Superconducting DC Homopolar Motor (http://atg.ga.com/EM/defense/dc-motor/index.php)
8)
Notice that they emphasize on the field coils must be superconducting. Why couldn't they use a strong PM? It also occurs to me that Gotoluc experiment saying that power output isn't about input current but it's all about how strong the magnetic field we have.
Quote from: GibbsHelmholtz on 2012.04.14, 13:31:27
Notice that they emphasize on the field coils must be superconducting. Why couldn't they use a strong PM?
I suspect because their numbers are so huge. 36 Megawatt.
Quote from: GibbsHelmholtz on 2012.04.14, 13:31:27
Notice that they emphasize on the field coils must be superconducting. Why couldn't they use a strong PM? It also occurs to me that Gotoluc experiment saying that power output isn't about input current but it's all about how strong the magnetic field we have.
1. Gibbs, can you point to (URL) "that Gotoluc experiment", pls? I have respect for his work.
2. Harvey -- very interesting. I understand this to be an example of magnetohydrodynamics, and I'm thinking the ocean-water is used to provide the moving conductor, to provide thrust to the (Navy) ship. Am I close?
Professor,
This is one of his latest experiment vid.
http://www.youtube.com/watch?v=OxuotFUWVGQ&list=UUwXI4FD09cVYyofvzF2sUrA&index=2&feature=plcp
He try to increase output by stacking up magnetic field which is easily seen with equations and related to magnetohydrodynamics drive.
F = iL x B or F = qV x B
Luc can see the term i or q as input and F as output. The amplification factor would then be magnetic field B .
I have a great deal of respect for the efforts of Luc, as well.
The first question I would ask myself is, what determines the amount of lift or stroke length under load?
I will offer that the stronger static field provides for quicker coil movement to the attracting polarity. With a weaker static field, velocity is slow enough that all the stored energy is dissipated before the coil reaches the attracting polarity.
Wow!
That is a whole lot of hoopla in one video :D
Thanks, Gibbs.
And here is the thread for the GotoLuc work: http://www.overunity.com/8429/mostly-permanent-magnet-motor-with-minimal-input-power/
I put together various versions of Faraday's homopolar motor, as my wife and I visited family from Maryland to Missouri to Utah in the last several weeks. Fun and educational. Perhaps you will find something that YOU would like to build. It's quite easy (see videos) and fascinating to study. The simplest version, shown in the first segment, requires just one 1-inch diameter disk magnet with conducting coating (about 3 mm thick), a 9" piece of 14-gauge wire, and a battery (C-cell or AA-cell is best). You can buy the needed neodymium/rare earth magnet(s) from supermagnetman.com and other sources. I went to a hardware store to get the copper wire -- pulled one wire out of ordinary electrical wiring for a house. Note the ground wire has no insulation and is easiest to use.
The next-to-last version shows the screw and entire system suspended by a thread. It is interesting to see the motion of the wire and the battery+magnet as the wire intermittently (on its own) touches the metal-casing on the neo.
http://www.youtube.com/watch?v=YfKzleMWE60
I've been studying the characteristic of motors and graphs of torque, rpms, efficiency etc...
It seems that the elimination of BEMF in motors are desire to achieve high efficiency, possibly greater than 1. I do not see how BEMF can be totally eliminated except to suppress it enough to not effect the torque. When looking at a motor in general, torque decreases as RPM increase. The cause of course is BEMF. The efficiency is:
effiency = Torque x RPMs / U*I
U*I is energy from a battery. Let's say we operate at region where speed starting to give BEMF that decrease input current by half. We have saved half of the potential input energy, RPM increased proportionally, but torque is now decrease by 4 times. The overall efficiency doesn't change much. If current input and torque stays constant with RPM, then efficiency only increase and possibly exceeds 1.
Homopolar motors can put out constant torque for a large range of RPMs. The reason being BEMF is relatively small for homopolars. This can also be achieved with pulse motor, however, the drive coil has to be small in inductance as possible. This allows us to operate at high speed and constant torque. Inductance reduction can be achieved in various ways such as low turn coil, bias magnet etc...
Hurray! I succeeded with my first homopolar GENERATOR! Photos below will help a brief explanation.
First, I designed a simple motor using a 1" diam neo magnet with metal casing, held magnetically to a short/fat bolt. (Extra mass helps keep it spinning during the generator phase.) This in turn holds to a screw which I punched through a box to hold the system from above. The screw-tip provides a good "bearing".
1.5 V is applied from a DC power supply shown, and the 1.77 A is typical for revving up the motor. +1.5V to the screw, ground via contact wire to the rim of the magnet-disk.
Then, with the magnet+bolt spinning magnet spinning and power supply disconnected, it now has a potential due to {E = velocity X B effects} -- that is, it serves now as a generator. Yes, even with the magnet co-spinning with the bolt.
To measure the effect, I have connected one probe of an ammeter to the screw and the other via a separate contact wire, touching the rim of the spinning magnet. One hand holds the contact wire, the other hand holds the camera -- and you see 0.9 mA measured on the meter produced by the simple homopolar ammeter, demonstrating output power from the homopolar generator.
This experiment was repeated several times. About 1mA current was typical. The voltage will be small with such a small diameter rotating magnet and has not been measured, but current generation has been demonstrated and measured.
Note: I am seeking (long-range goal) to extract power WITHOUT any external (non-moving) brushes or contacts...!
I would be interested to hear if anyone thinks this is even POSSIBLE. Thomas Valone experiments, etc., may suggest it is not possible. I wonder what he thinks about this today...
I say we just connect the homopolar to rotating magnets and coils to extract power. No brushes for generation there.
I just thought of some way of loading. I am analyzing which method of loading is the best for energy and torque drag on the generator. There seems to be better ways than others for energy we get. Anyone has an opinion on this? If we increase the number of coils, we get more energy for stacking resistance and less drag for reducing turns.
Quote from: GibbsHelmholtz on 2012.05.09, 13:54:07
I say we just connect the homopolar to rotating magnets and coils to extract power. No brushes for generation there.
Thanks, but how would you do the connecting? and extract power?
My idea lately was to have two conducting disks on the same shaft, but separated by say 10 cm or so, and one with NtoSouth to the right and the other, NtoSouth to the left. That way, when the shaft is spun, the rims acquire OPPOSITE charges (also the area near the shaft)... and one should be able to extract power by allowing current flow between the rims -- also, between the disk-central areas, which would need to be insulated from the shaft.
Quote from: PhysicsProf on 2012.05.09, 20:44:24
Thanks, but how would you do the connecting? and extract power?
My idea lately was to have two conducting disks on the same shaft, but separated by say 10 cm or so, and one with NtoSouth to the right and the other, NtoSouth to the left. That way, when the shaft is spun, the rims acquire OPPOSITE charges (also the area near the shaft)... and one should be able to extract power by allowing current flow between the rims -- also, between the disk-central areas, which would need to be insulated from the shaft.
My thinking was to connect the homopolar motor to a generator via gear coupling or belt.
I think your mode of power extraction allow for high current to flow, but the voltage is too little even at high speed. Higher current would also create a torque to stop the disk.
I think I've made a mistake assuming that torque is proportional to current squared. I'm based on force between magnetized core. If one is electromagnet and one is permanent magnet, the pole of permanent magnet doesn't change strength, leaving torque is a linear function of current. The efficiency formula then:
efficiency = Torque x RPM / U*I
If input current go down by 1/2 due to BEMF, then Torque also go down by 1/2 as RPM increase. Efficiency would actually go up proportional to RPM. Hm.... So to have high efficiency, we actually needs to operate at the region where BEMF dominate. The torque would be so low, power so low, but we could exceed COP 1.
Quote from: PhysicsProf on 2012.05.08, 16:26:54
Note: I am seeking (long-range goal) to extract power WITHOUT any external (non-moving) brushes or contacts...!
I would be interested to hear if anyone thinks this is even POSSIBLE. Thomas Valone experiments, etc., may suggest it is not possible. I wonder what he thinks about this today...
I have often though about this question for the Faraday disk generator and I didn't find any solution.
For instance, if you connect directly the rotating disk (axis and rim) with two flexible wires able to wrap when the disk rotates, there is no DC because there is a reverse effect of the Lorentz force onto the electrons in the wires that are now crossing the magnetic field with a not nul speed.
I have also tried with a capacitor rotating with the disk and connected between the rim and the axis: it doesn't charge for the same reason.
It's a question of relativity. We must have a referential at rest, and one at a speed v, and let pass the electrons from one to the other. There is a potential difference neither in the referential of the disk nor in that of the circuit at rest. It comes only from the speed gap.
Quote from: GibbsHelmholtz on 2012.04.11, 12:58:34
...
I'll do the experiment today to see if polarity change.
I've tried to analyzed the forces on Harvey's drawing. The red line indicates Lorentz force pushing the loop out of the page. However, notice that the blue force on the magnet section is pushing the magnet into the page. If we add the blue to the red, the forces exactly cancel out to zero!
...
Therefore, the conclusion is... the net force is zero! no movement. ;)
(http://www.overunityresearch.com/index.php?action=dlattach;topic=1411.0;attach=7722;image)
It's logical. There is no movement but only if there is no sliding contacts.
The "red" Lorentz force applies to the wire and the blue one, to the magnet. So in case of sliding contacts, if you maintain at rest one of the two objects, the other one will rotate under the effect of the force.
(Sorry for the delay of my reply).
Quote from: exnihiloest on 2012.05.10, 08:16:35
It's logical. There is no movement but only if there is no sliding contacts.
The "red" Lorentz force applies to the wire and the blue one, to the magnet. So in case of sliding contacts, if you maintain at rest one of the two objects, the other one will rotate under the effect of the force.
(Sorry for the delay of my reply).
Welcome back,
Yah, relative motion is require for sure.
Glad you're back, hope everything doing well over there. I'm just struggling right now to find out is the torque of motor linear or squared to current of the coil, then I would go on to which flavor of OU I want. lol
Quote from: GibbsHelmholtz on 2012.05.10, 13:30:44
...
hope everything doing well over there.
Yes, thanks.
Quote
I'm just struggling right now to find out is the torque of motor linear or squared to current of the coil, then I would go on to which flavor of OU I want. lol
The torque is proportional to the force, the force is the Lorentz force which is proportional to the current, therefore the torque is linear with the current.
The homopolar generator or motor is an old story of free energy since Bruce De Palma pretended to have overunity and an engineer confirmed it with measurements which finally have been shown to be flawed. The "paradox" of the Faraday disks is only apparent when one doesn't understand the underlying principle of relativity and to which objects it applies. These machines are very conventional, there is not one anomaly nor a theoretical idea about them able to challenge the academic knowledge. Without new elements, for me this is a dead-end for the free energy.