Faraday Homopolar Generator - Current Flow Question

I think it must be due to the evidence of dihydrogen monoxide in proximity to a charged rotational mass.

You steam engine punks....

Always trying to push DHMO on everyone, proclaiming its benefits and downplaying the dangers of inhalation.

Thank you for posting, all the same.

Hi Foamy!

You state, "Why does current flow from center to outer circumference in a Faraday homopolar generator . . .?," [under several conditions].

Who says it does? Faraday??? Next door neighbor???

I'm afraid i cannot answer your question directly, however I thought I would give you a few things to consider. the first is have you considered Hall effect? Thesecond is to consider a synchronous (Brushless or cage rotor motor) where the armature is a series of metal discs clamped together. third is carefully consider the path of the current in the disc. I surmise that it may well be a tight spiral rather than a straight line to the edge; i suspect that this would give the result you seek.

Further to my last email you should look up Wikipedia. It seems there is no current flow per se in th edisk, the contacts wipe off electrons by frictional processes similar to a Van De graf generator and as the inside electrode travels less distance than the outer electrode a potential difference is created between the two. Hence direction of rotation doesn't matter

No they don't

Hi,

are the armature discs unclampable and what are they made of? What sizes are they?

I saw a rather interesting spinning disc filled with fluid and metal particles at a science museum the other day that made me think about the point you made about the tight spiral. It was supposed to mimic and visually display a hurricane weather system.

These photos were taken at various spin speeds and with disc span and then stopped.

The "spokes" are the same size from axle to rim so the magnetic field affects the "spokes" evenly. Not so with a solid disk or pie wedge.

If you look at it in terms of the variable area from the center to the edge of the disc being unevenly influenced atomically by the magnetic field, it makes more sense that such a physically unbalanced condition of the disc spinning in a magnetic field would produce a monodirectional current regardless of direction of spin.

While the modern Maxwell's equations describe how electrically charged particles and objects give rise to electric and magnetic fields, the Lorentz force law completes that picture by describing the force acting on a moving point charge in the presence of electromagnetic fields. The Lorentz force law describes the effect of Electric and Magnetic fields upon a point charge, but such electromagnetic forces are not the entire picture. Charged particles are possibly coupled to other forces, notably gravity and nuclear forces. Thus, Maxwell's equations do not stand separate from other physical laws, but are coupled to them via the "charge and current" densities. The response of a point charge to the Lorentz law is one aspect; the generation of Electric and Magnetic fields by currents and charges is another.

If the pie shaped pieces were replaced by copper spokes they would behave as you previously described - like a grade school science project.

I wonder why they always used a galvanometer instead of a current meter.

It is a current generator and I would expect a much more active response with a meter that matches the low impedence of the generator.

Hmm where can I find a nice copper disc and a powerful magnet?

Jon

I would like to thank all respondents and I would like to retract my question. The critical difference has been uncovered by the forum and it is not with the shape of the disk nor wires, but with my original flawed comprehension of the material.

I appreciate the help pinpointing the problem. I hope the next post requires a true engineering solution, and not just a remedial reading comprehension course on my part.

What did I miss? I don't see a good explanation in any of the responses here. Why the mention of material - any conductor will work here.

The theory about 'scraping off electrons' completely ignores the necessary presence of the magnet. And common sense.

Some of the answers on this thread frighten me - I hope these are not practicing engineers.

JayGeeBSE.

Presence of magnet not necessary.

Common sense isn't it?

Could the outer circumference be acting as a sort of "ground" since it has alot more mass than the center.. and the electrons will take the easiest possible path to ground; all you're supplying with the magnet could be the voltage potential to get the motion started.

Just a thought..

You may have answered your own question! With the disk, the magnatic flow is either

clockwise or counter clockwise and this is something that is easily seen but with the

wire the flow would spiral which is not so visual so, the answer is geometry.

Because electric current can be considered as a fluid experiencing centripetal acceleration due to the rotation of the disc it is present in. This is how the earth surface is full of electrons and how it has a magnetic field. consider the disc as an equatorial slice of the earth sphere, earth being a very good conductor. the earths surface is a bunch of electrons stuck at the earths surface and spinning around in a circular path at high speed as the earth spins. moving electrons create a magnetic field.

ie. if the earth rotated in the opposite direction, the poles would swap over. until then it will remain as it is.

So... the magnetic field from the magnet is not required to measure current and potential difference, as simple testing will prove to you. Its just due to rotational inertia. Go on, lose the magnet. You'll still measure voltage and current.

So therefore, a cable connecting earth at the equator to earth at a pole (spin axis) will measure potential difference and pass almost limitless current. Who needs oil eh?!

We just need a darn big, long cable.

I'm not sure you'll read this explanation anywhere else, cause I didn't.

Now the question I want answered is - why does the earth spin in the direction that it does? Do all spinning planets spin in the same direction? And then, those that do would necessarily have the same magnetic pole orientation relative to spin. Unless they were made of rock and not metal perhaps...

Hi Christoper,

I read your Faraday Paradox explanation on Wikipedia and was interested by your mention of measuring current and p.d. in the absence of the magnet, i.e., by just spinning the disc.

It appears that the results of Kelly's experiments comprehensively demonstrate that the Faraday 'paradox' is merely due to experimental oversight (read: carelessness). Basically, most experimenters, including and since Faraday, forget to include the relative motion of the measuring circuit as a factor in their experiments or their subsequent explanations; a prime demonstration of the concept of the Elusive Obvious.

However, as comprehensive as his tests were, Kelly does not report on performing the tests without the magnet - as you have. (See "Faraday's Final Riddle; Does the Field Rotate with a Magnet?") His focus was on demonstrating the source of the paradox, and it's elimination. I hope to comment on your observation and subsequent conclusion.

I'm not sure of the exact layout of the machine you tested, but in general, the arrangement seems to be a conducting material for the (rotating) disc and a *dissimilar* conducting material for the (usually stationary) contacts.

First a few observations:

1. It is known that rubbing two dissimilar materials has the effect of developing what we call electro-static charge. (Whatever that is - I don't consider it an explanation to assign a name to an observed phenomenon, and then proceed to use that name as a response to the question of: 'why it is so?')
   
   
2. It is also known that rubbing two materials together has the effect of increasing their temperature due to the work done against 'friction'. (I'm my opinion, "due to work done against friction" is not an explanation either, merely a description.)
   Prof Seebeck originally showed that heating two dissimilar materials connected in a series circuit with a galvanometer, produces a deflection on the meter (i.e. electrical 'current' flows.) This is called a thermo-electric couple.
   

(NB: Refer to 'Chapter I: Electricity of Friction'; and 'Chapter III: Electricity of Heat' in 'The Story of Electricity' by John Munro for further details of the above-mentioned observations and a general synopsis of electro-effects. You can find it in the text section of archive.org)

Assuming the machine you tested (in the absence of the magnet) had a rotating disc and stationary contact leads, we can see that 'friction' cannot be ignored as a factor to correlate the observed current and p.d. At the very least, friction between the edge of the disc and the lead in contact with it should be considered.

If the contact leads were of a material dissimilar to the spinning disc's, then it is possible for at least either observation to correspond with your observed result.

As can be seen, there is no need to appeal to the centripetal migration of electrons just yet. 'Friction' between the disc and the contact lead on the outer edge has to be considered. It is entirely possible that the fictional electro-static charge, or the thermo-electric coupling effect of the resultant temperature increase do not sufficiently account for the observed current and p.d. However, they must be addressed and satisfactorily eliminated before proceeding to the 'electron centripetal migration' idea.

To entirely eliminate 'friction' as factor, you would have to eliminate the relative motion of the contact leads and the disc, i.e., in the absence of the magnet, spin the WHOLE circuit - the disc, connecting leads and galvanometer. (Incidentally, this would be similar to test 'k' from Table 1 in Kelly's paper, but without the magnet. Kelly does not mention carrying out this test with his apparatus.) If no current or p.d. is registered, then the friction due to the relative motion of disc and contact leads is the culprit.

This should be corroborated by keeping the disc stationary while spinning the remainder of the circuit - i.e., the connecting leads and galvanometer. (This would be similar to test 'n' from Table 1 in Kelly's paper, but without the magnet.) Registering a current or p.d. while the disc is stationary and the remaining circuit rotates provides further support for friction being the culprit. Since the disc was not in motion, this would also disprove the hypothesis of the current or p.d being due to the centripetal migration of electrons - whatever those are - to the edge of the disc.

In summary, perform the following tests:

A. in the absence of a magnet, spin the whole circuit - disc, contact leads and galvanometer;
B. in the absence of a magnet, keep the disc stationary and spin the contact leads and galvanometer.

If Test A produces a positive result and or Test B produces a negative result, then 'friction' is off the hook. (The satisfying of both conditions strongly eliminates friction.)

If Test A produces a negative result and or Test B produces positive result, then 'friction' is responsible. (The satisfying of both conditions strongly points to friction.)

(Considering theoretical combinations, the other outcomes are that: either both Tests A and B are positive; or both Tests A and B are negative... however, intuitively, these outcomes seem unlikely.)

You should then use similar materials for the disc and contacts to perform the tests. Negative results should strongly support the hypothesis of the current and p.d. you are measuring to *corresponds* to that produced by frictional electro-static discharge effects and or the thermo-electric coupling effect.

It is important to note that 'corresponds' does not mean 'explains'; an explanation would provide a physical model and coherent descriptions of what 'electrical current', 'heat' and 'friction' are within the framework of that *same* model; instead of an amalgam of different physical and mathematical models perforated by inconsistent descriptions of the phenomena these words represent - this is how we end up with countless so-called 'paradoxes' and 'dualities'.

Regards,

K.

>>>...ie. if the earth rotated in the opposite direction, the poles would swap over. until then it will remain as it is...<<<

I am curious what your opinion woudl be if presented with persuasive evidence that the Earth's magnetic poles have switched with some regularity about every 200,000 years. Would that suggest to you that the Earth has switched rotational direction about every 200,000 years?

Hi benbenben,

I would love to be presented with such persuasive evidence. Show me!

It might suggest a number of things to me, one of which would be that the earth switches rotational direction.

How long between ice ages again? (10,000 years?) How long between periods of utter destruction on the face of this lovely spinning globe we all call home? When did the dinosaurs go extinct? (65 million years ago?) Where did that coincidental thin layer of iridium come from? (The sun?) How long since the last pole change then? When was the earliest recorded evidence of human existence? Has mankind lived through a pole change? When is the next one due? Who will get to sit it out in a space lab till the magnetosphere builds up to provide its protective shield once more, and then swoop down from the skies to start repopulating the earth? etc. etc. etc.

Christopher Culley:

Persuasiveness is in the eye of the persuadee, so I will provide you with evidence I find persuasive (not necessarily definitive, but persuasive none the less). I look forward to your opinion.

The argument goes something like this:

In areas of volcanic activity and other areas where molten lava has cooled, ferrimagnetic material aligns with the earth's magnetic poles.On volcanic flows otherwise date-able on land and on the areas of seafloor spreading, a pattern of reversals emerges, where the magnetic alignment reverses abruptly. At times the reversals are fairly regular at a period of a couple hundred thousand years and at other times there have been much longer stretches.

The sea floor is striped with these tell-tale magnetic reversals, that approximate a reversal on average every couple hundred thousand years, assuming a fairly constant rate of seafloor expansion in those areas.

Well, its not really evidence is it. Its more like an executive summary.

Where is the test data available for review? Can you reference the report? I find this fascinating and fundamental. How interesting. Does anyone have any ideas that might explain how this might happen? Because I don't, yet.

When was the last indicated reversal? Have there been any in the last 10-30,000 years?

Here's an idea. The sun is a hot thing in a vaccuum. like a vacuum tube hot filament,it emits high energy electrons in a constant stream. Lets say the earth sits in an electron flow, flowing out from the sun. 2d model like spokes on wheel. The earth is an iron ball in centre, concentrating magnetic field lines from electron flow outwards from sun and around atmosphere, or is that magnetosphere. What happens is cold spot on sun emits less electrons and electrostatic field reduces at this point and electron flow from space charge to cold spot results. When earth passes through this local electron flow reversal during yearly orbit, the magnetic field reverses polarity.

In this model, earth magnetic field only result of passing through field resultant from electron flow outward from sun, and concentration of flux lines through soft iron core.

Just a thought. That's just off the top of my head, I'll try and think it through a bit more.

Does this account for wandering poles, and field strength changes in terms of electron flow due to sun surface temperature variations?

Has anyone tried shooting an electron beam at, or just to the side of, a soft iron ball bearing in a vaccuum to see what happens?

Anyway, very interesting data. I'd like some more. Where do you read this stuff?

succinctly - electrons have mass (charged) and are subject to inertial forces under rotation - they are flung to the outer edge of the disc under rotation - in either direction of rotation, the centripetal acceleration acts outwards towards the edge of the disc.

The magnet is not required, but can add or subtract to the effect, according to Flemings law.

I have found by testing that both voltage and current increase with speed and I suspect they are proportional to velocity squared, but will have to confirm that with you later after more tests. I will also confirm the reversal of magnetic polarity at spin axis, with direction of rotation.

Hi Chris,

I pondered you comments:

By the same token Protons have mass (charge), a much greater mass than Electrons, and are also subject to inertial forces under rotation - they would also be flung to the outer edge of the disc under rotation except that mother nature says the molecular matrix must stay fixed but the electrons can fly free.

The Nucleus tries to hold the Electrons but the Electrons are more freely parted with.

G force is great at the outer edge of the spinning disk and small at the center.

If what you say is true, "both voltage and current increase with speed", if you spin the disc fast enough you would only need "brushes" very near but not in contact with the center and outer edge because the voltage would be high enough to jump the tiny gap.

I would like to hear the results of you experiment.

Also:

I heard long ago that a suspended copper or brass disk passing quickly through a strong magnetic field would be caused to slow down and mechanically oscillate due to the induced current and resulting magnetic field opposing the external field.

I considered this when I saw the info on the Homopolar Generator.

You have anything about this?

Jon

Hi Jon,

"Sea of electrons" !

I did actually hear an account that a spinning copper disc gave sparks from the outer edge, but I can't remember where I read that, but it stuck in my mind. Isn't there some charge seperation in air dielectric surrounding disc edge as per the weather rolling up the leading side of a hill range and the lightning and rain falling on the other side? (Contact charge transfer between dissimilar materials as per van der graaf belt and rollers?) Its certainly an effect I'd like to confirm and I like your suggestion of brushes close to disc edge - like what's in my van der graaf generator and is used on Wimhurst machines. I'll give it a go and let you know. I'd like to discuss more with K first about a comprehensive test rig and method for best results for interpretation.

I'll be happy to let you know the results of the experiments. Glad you're interested. I think I might have sourced a company in Philadelphia who seem to sell a range of 16ga thick copper discs up to 12" diameter.

I'll try and give them a call tomorrow. I haven't had much luck with local machine shops turning copper discs so far.

But you will have to be patient for results because I'd like to be methodical about it. I've seen enough to want to do it properly.

On your second point - It sounds a bit like that fun trick of dropping a close fitting round magnet through the inside of a copper tube and it falling slowly because of the same effect you describe. I'll try the disc experiment you describe when I get one, and let you know. Or I'll try and find an old grandfather clock, and rip apart my microwave oven (great magnets!)

Thanks Chris,

I will be glad to hear anythink you turn up.

I used to have a radar magnetron magnet. Stuck it on something and lost it.

The microwave stuff I worked on used electromagnetic lenses on 5.5 foot high Klystrons.

"dropping a close fitting round magnet through the inside of a copper tube" sounds intriguing. Haven't tried that.

Jon

You must have been cooking for alot of people...

Only if they put their heads in front of the feedhorn.

10 kiloWatt output.

The effect of dropping a strong magnet through a tube made of a good conductor is worth seeing....and it doesn't even need to be very close fitting....

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Seeing how slowly an aluminum plate falls in an energized MRI is even more impressive.

When I was in High School (late Jurassic period) I went on a field trip to UC Berkeley to see the Cyclotron. They let us play with an aluminum pizza tray from Kip's in the magnetic field of the Cyclotron. It was amazing! The shock of the experience turned me into an engineer! (eventually)

I am very interested in your comment that a homopolar generator's current always travels from the center of the conductor disk to its peripherry regardless of the direction of its rotation or a change in the polarity of the magnetic field. I am interested in the references for this phenomina

John R Warfield M.D.

My email address is warf1002@aol.com

Hi John,

This was personal test observation and discussion with some of these guys was very interesting and led to the consideration that it might have been caused by a temperature effect between dissimilar metals of sliding contact and disc surface. Further investigation and confirmation of this suggestion has been on hold for a while as I attend to other business, but the project is still active.

It certainly made me think and ask questions.

I would be happy to discuss further.

Christopher

I am very interested in your comment that the direction of the current is a homopolar motor is always from the center of the conducting disk to its peripherry regardless of the direction of rotation of the disk and irrespective of the polarity of the magnetic field. I am interested in the sources of this information. If you could respond I would appreciate it. If anyone else knows on this blog I would also appreciate the reference.

John Warfield M.D.

Direction of current flow in a homopolar generator follows all the same rules as current anywhere else. It is dependent on direction of rotation and polarity of B field. It was confusing to me that when you put copper washers on both sides of a axially polarized ring magnet and spin the assembly that the current in both washers goes in the same direction depending on the direction of rotation. But B-field flow is from North to South, so both conductors are following the rules.

I'm not clear on what all the theorizing is about.

"I am but an egg." - Michael Valentine Smith