Quote by MS La Moreaux Claude, FL is purported to cover both transformer and motional EMF. Motional EMF is mistakenly supposed to be the result solely of flux change. Either it is or it is not. If FL is supposed to cover motional EMF, it would have to do so in every case, including those where the flux change is zero. You see that motional EMF is independent of flux change. It should never be associated with flux change. They are two completely different phenomena. Again, motional EMF and what you are referring to as Lorentz are identical. There is no magnetic flux involved in optocouplers. They act as switches. They do not really transfer energy between systems so much as transfer a signal. They have nothing to do with electromagnetic induction. Mike
Please review the attached, as it explains the HG using SR. In a nutshell, the Lorentz force moves electrons towards the center of the disk and holes (+ve charge) towards the rim. This charge separation results in a static E field and potential. Separation of charges explains the static nature of the E field. The current density J is related per J=sigma*E, which is Ohm's law.

Regarding FL, you firmly state that FL is valid for xfmr induction, i.e. time-varying flux. You state that it must be true always, and that with static flux, no inducton can take place. Yet a Hall effect current sensor produces induction with static flux. A xfmr cannot do this. So there is something else going on here. In a HG, the flux & induced current/voltage are static. FL relates the induced I/V to the change rate of the flux. Motional emf/mmf is due to the flux spatially varying so that the actual flux encountered by the circuit is time changing. Moving through a spatial flux change results in a time varying flux in the circuit reference frame.

Thus if phi varies with spatial position r, and velocity u is dr/dt, then d(phi)/dr * dr/dt = d(phi)/dt, by the chain rule. So FL covers this aspect of induction. Moving through a flux that is static wrt time, but varying wrt position, is equivalent to sitting still with the flux time-varying.

The HG is best explained by Lorentz force & relativity. Remember in a HG, we set the electrons in motion by expending energy in rotating the disk. Then the magnetic field acts upon the moving electrons per Lorentz. Charges are separated and a static E field is formed, with a dc voltage & current.

E fields induced per FL are solenoidal. No sources or sinks exist, they have rotation, & are non-conservative. E = -dA/dt, where A = magnetic vector potential, B = curl A.

E fields in the HG have sources and sinks due to charge separation, have no rotation, are conservative, and E = -grad V, where V is scalar electric potential.

Clearly the E fields in the HG are markedly different than those in FL type generators. This is a different mechanism, likely related via relativity.

Optical is energy. Have you seen what happens when sunlight is focused through a magnifying glass into a point and focused on a piece of paper? No energy?! Indeed!

That's all for now. Let's review the paper and discuss further later. BR.

Claude
Attached Files
 q218unipolar.pdf (342.0 KB, 7 views)
 One more thing should be mentioned. According to Maxwell's published law of Faraday (1873): curl E = -dB/dt. What is he saying here? If the flux time derivative is zero, is E zero? Of course not. He's saying that the curl of E is zero. In the HG case, that is exactly what is measured. The Lorentz force due to electron motion relative to the static field acts radially so that plus & minus charges are separated, center & periphery, resulting in an E field radially. But this E field is due to charged particles. It has no curl. Maxwell/Faraday predicts just that. A non-rotational E field. The HG perfectly affirms and vindicates FL per Maxwell. Transformers & motors/generators OTOH, per Faraday induction, exhibit E fields with curl. So there is no paradox after all. Maxwell & Faraday got it right all along. I'm glad that's settled. Good day to all and feedback is welcome. Claude

I'm not sure if this is helps or not, but for what it's worth, in Daniel Fleish's "A student's guide to Maxwell's Equations" he distinguishes b/w the convenient Flux Rule, which is a handy formula, and a modified version of Faraday's Law, which is more subtle and rigorous, and, he believes, correct. I'll post the quote and formula if I can find it.

Regarding Feynmann's quote, I found the likely source in the Wikedia article Faraday's Paradox in the section Inapplicability of Faraday's Law

 The "flux rule" does not work in this case. It must be applied to circuits in which the material of the circuit remains the same. When the material of the circuit is changing, we must return to the basic laws. The correct physics is always given by the two basic laws

-- – Richard Feynman  The Feynman Lectures on Physics

Just after the Feynmann quote, the argument is made that once SR is taken into account, Faraday's law holds true. I don't know enough to pass any judgment, but at first pass it seems Feynmann is arguing more against the universality of the handy flux rule, but not necessary the fully expressed Faraday's law w/ perhaps SR taken into account.
 Claude, I did not say that with static flux, no induction could take place; I said that that is what FL implies. That is one reason why FL is false. Flux change due to motion is not physically (in the sense of physics) the same as time-varying flux without motion. That is the whole crux of the matter. The two have completely different physical results. The former leads to motional EMF and the latter results in transformer EMF in accordance with one of Maxwell's four classic laws. When you say that E fields induced per FL are solenoidal, you are mistaken. That is only true when there is an intrinsic change in the flux. It is not true when there is motional EMF. FL does not distinguish between the two, which is why it is false. Light is certainly energy. But energy transfer in an optocoupler, though necessary, is incidental to the transfer of a signal, which is the purpose of an optocoupler. Mike
 diagopod, The flux rule discussed by Feynman is exactly the same as what we are referring to as Faraday's Law in this thread. Relativity is really irrelevant, as it came along long after FL. FL is very simple and simply false, as I have demonstrated earlier in this thread. Mike

 Quote by cabraham But [b]u X B[/b} IS included in FL. I've stated this repeatedly, but you won't listen. One more time. Oh yeah, you said "You are not the first post graduate that I have run across that did not know what he was talking about". Well, how much experience/skill do YOU have with motors, xfmrs, generators, induction heating, etc.? Is there any transducer work in your past such as microphones, speakers, etc.? What have you done to be the expert on motional emf? I'm not attacking you, but I'm just curious what makes you think you are head and shoulders above qualified experts. You have a BS, a good achievement. A BS qualifies you to do some good work in science to produce products that benefit mankind. But to topple established axioms requires much much much much more. A PhD in phy or EE is still not enough. You'd need a huge lab, budget, and staff with accelerators, scanning microscopes, etc. to advance Maxwell's equations to a new level. Your BS is a useful degree which empowers you to a limited degree. Even should I get my PhD, and with my 32 yrs. of engr background, I am still NOT qualified to topple Faraday. Here's what you and I have in common - we both have limited knowledge. Here is where we differ - I am well aware that my knowledge is too limited to go challenging Faraday. Nothing personal, thanks for the interesting chat. Good day. Claude
Hey, Claude, don't say dumb things and then run off! Where did you ever get the idea that somehow "credentials" are needed to topple Faraday's law? And where did you ever get the idea that real science is only done by spending vast sums of taxpayer money? Are you getting your paycheck from the government or something? And why wouldn't 32 years of engineering background qualify you to challenge Faraday? Hey, you live in the 21st century and Faraday, though smart, didn't know squat compared to you!

The truth is (and I sure hope you are not spreading your errors among the young) that science is done with the MIND! It all starts between the ears. I don't care how much money you spend, if you can't think it won't be science!

And the truth is that Faraday's law as typically stated IS wrong (but interestingly NOT wrong according to how Faraday stated it!). Does anyone here understand how the rocking plates work? Why doesn't the changing flux give a voltage? Here, I'll explain it to you guys. Here's the equivalent idea and one more case where Faraday's supposed law is invalid.

Imagine a large rectangular loop of wire with a meter in the circuit. Imagine a magnet putting a local flux through an area in the end of the loop near the meter. Imagine a wire and a switch connecting the sides of this loop that when thrown cuts it into two loops. Now move the magnet to the other end of the large loop (nothing happens as flux enclosed in loop has not changed). Now close the shorting switch. Remove the magnet. Open the switch. Voila. The flux has gone from max to zero and the meter does not move! Faraday is invalid!

But the error that makes Faraday's law misinterpreted is that one assumes that a changing magnetic field (flux) causes an induced E field. (An E field in a conductor creates a current) Sorry, the equation Curl E = -db/dt or as often stated EMF = -dB/dt are TRUE relations but they are not CAUSAL relations!

You need to understand what that means. It means that while the value of an induced E and a magnetic field are RELATED they DO NOT cause each other. Hence a voltage is NOT repeat NOT created by a changing magnetic field! If one examines the causality of Maxwell's equations one finds that BOTH magnetic and electric fields are BOTH created by ONLY by charges and their motions (currents). Hence an induced EMF is created by a current somewhere as it's source. And that current ALSO creates a magnetic field. BOTH are related (as they come from the same source) by Faraday's law in many cases, but the changing magnetic field is NOT causing the EMF! Indeed even in the case of moving magnets one can show that the EMF is created by the moving atomic CURRENTS that create the fields of the permanent magnets.

Hence, as Feynman clearly states, Faraday's law is NOT valid for all cases. In cases for example where the configuration of our setup is changing (our switching example) it simply does not work. It didn't work in Faraday's time either as proved by the generator bearing his name! Which is why Faraday NEVER said that a changing magnetic field induces an EMF. He said that a changing CURRENT can induce another current nearby! Obviously even though Faraday didn't have much of a clue, he still knew more about the subject than all the "modern" physicists with their PhDs, money, accelerators and scanning microscopes! OK?
 bjacoby, Well, at last a posting that supports me! Believe it or not, yours is the first since I initiated this thread. Thanks. Mike
 Mentor Blog Entries: 28 If you guys do not stop snipping at each other and do not go back to strictly discussing on-topic subjects, this thread will be closed! Zz.

 Quote by ZapperZ If you guys do not stop snipping at each other and do not go back to strictly discussing on-topic subjects, this thread will be closed! Zz.
I'm amazed that a thread like this is even allowed to exist in this forum. I wasn't aware of it till now. I did a one minute scan and found many statements of misinformation. For example it was claimed that the Faraday disk violates Faraday's Law. Nonsense, it does not and the principle of operation of the Faraday disk is not even based on Faraday's Law.

Mentor
Blog Entries: 28
 Quote by elect_eng I'm amazed that a thread like this is even allowed to exist in this forum. I wasn't aware of it till now. I did a one minute scan and found many statements of misinformation. For example it was claimed that the Faraday disk violates Faraday's Law. Nonsense, it does not and the principle of operation of the Faraday disk is not even based on Faraday's Law.
This thread IS being reviewed right now. In the meantime, please feel free either to respond, or to report the offending posts.

Zz.

 Quote by cabraham You treat magnetic fields as fictituous, pseudo, & derived. Yet Einstein emphasized in his 1905 paper, that elec & mag forces are equally important, and that neither is the "seat". Nobody has successfully refuted this viewpoint. So in a nutshell, the OP claimed that FL is false. What are you saying? Is FL true or false? Please answer. You gave your treatise but never answered the original question explicitly. Thanks in advance. Claude
Can you explain this a little more than you have. It seems that a person could clearly isolate charges and then measure their relative velocities. And when we measure stuff, at rest, they have a force on each other. We can attribute this to the E field. I'll let you comment on that if you want. And I'll express my concerns a little bit below.

So, my misunderstanding is based on the fact that you 'can' find the relative velocities, and then measure forces. How is there a symmetry here? We can grab a physical thing that has charge and test it with another charged thing, and this force is observed when there is no motion. How do you account for the 'static' electric field? If you want to explian it with symmetry, it seems that the E fields would have to be due to some sort of moving magnetic charges, but since the E field is localized (not moving) and falls off as 1/r^2 (not a dipole field or something), then I don't see it. Thanks!

 Quote by elect_eng I'm amazed that a thread like this is even allowed to exist in this forum. I wasn't aware of it till now. I did a one minute scan and found many statements of misinformation. For example it was claimed that the Faraday disk violates Faraday's Law. Nonsense, it does not and the principle of operation of the Faraday disk is not even based on Faraday's Law.
I'm not amazed that as our discussion homes in on a careful evaluation of some basic physics dogma that some are ready to call for censorship. Any discussion that questions tradition is bound to get a bit messy! Let us take the above statement that a Faraday disk does not violate Faraday's Law. We all agree that a potential is induced in the disk. And that means an E field is induced in the disk. The standard argument is that an induced E field is created by either a changing magnetic flux or by "flux cutting". Obviously in a Faraday generator the magnet is fixed and the flux is not changing through the disk. So one assumes therefore it must be a case of "flux cutting". In the usual "flux cutting" case as the flux is "cut" the area of the flux changes and hence the there is ALSO a dB/dt. In the Faraday generator the area does not change. Even worse, the disk is continuous so there is no obvious "flux cutting" as might be the case if the disk were slotted. We know the disk nuclei are fixed and rotate with the disk but they can't move sideways to create a potential either! What the free electrons do is rather up for grabs. It's hard to make a case that they also are dragged around the disk as it turns. Hence both flux changing and flux cutting fail.

Well what does succeed? First let me note again that the proper statement of Faraday's law is that a current creates another current. There is no magnetic field involved at all! This is proper causality! So let us start with the magnet. How does it work? Well, it is believed that electrons circulating around the atoms create a current loop that creates a permanent magnetic field. One can show that for homogeneous materials this is equivalent to a larger current circulating about the outside of the magnet. cylindrical magnets and thin solenoids make nearly identical fields.

Now near that circulating current we have a rotating disk. So lets put the disk in one frame and the magnet in another. For drill lets rotate the magnet rather than the disk. So now we wish to calculate the electric field induced about the magnet. Well, if the magnet is still, there is none as the magnet material is electrically neutral. But what happens when the magnet rotates? Here is the crux. Remember that only CHARGE and CURRENTS can be sources of E fields! Hence the magnetic field does not matter!

So if one examines a neutral current moving with constant velocity in the direction it is flowing one finds that two E fields are induced One is an ordinary electrostatic E field due to the motion and the other is an Induced electrokinetic E field also due to the motion. It can be shown that in the case of a current loop rotating about its axis so the current has a constant velocity in the direction it is flowing an E field is induced equal to -V x B. But make no mistake here. This field is NOT caused by B! Just it's VALUE can be calculated using B! The induction is from a current loop DIRECTLY to the E field producing the generator potential!

Of course this is EXACTLY how Faraday stated his observations: "When an electric current is passed through one of two parallel wires it causes at first a current in the same direction through the other, but this current does not last a moment notwithstanding the inducting current (from a voltaic battery) is continued..."

Here we have the equivalent currents in the magnet creating a current (E field) in the surrounding space by virtue of their relative motion. If the magnet and disk are in the same frame, then there is no E field observed and no induced potential.

Hence Faraday's law as stated by Faraday is correct, but the traditional versions that ascribe the creation of an E field as being created by a B field are simply incorrect. The magnetic field is just something that is ALSO there. It has the same current source as the
induction and therefore is RELATED to it, but most certainly does not CAUSE the generator action.

It is the hard fact that ALL induced E fields are created by charges and currents and NOT by magnetic fields that means that Faraday's Law as usually interpreted is false.
 Mentor That is completely wrong. An electric field can be created by a changing magnetic field.

 Quote by bjacoby Now close the shorting switch. Remove the magnet. Open the switch. Voila. The flux has gone from max to zero and the meter does not move!
It depends on the size of your short circuit and the sensitivity of your meter whether there’s a deflection. According to Ohms law if your short circuit has a resistance (it has) and a current flows through the short (it does) there will be a voltage across the meter. By the way the current in the short is normally called an eddy current.

Disconnecting the meter temporarily, while you remove the magnet will prove your point as well?

As far as I can tell, your long explanation is basically saying that the electric field (force driving the electrons across the disk) is a VxB type interaction. Well yes, we know that. That is simply the well-known Lorentz force, which is the basic underlying mechanism that explains the principle of operation of the Faraday disk. The Lorentz force pushes the electrons either to the center, or out to the perimeter of the disk (depending on the field direction and rotation direction). The charge imbalance implies a potential difference. By tapping the voltage across the center and the perimeter, one is able to drive high currents, all due to Lorentz force. This is different than the typical generator which is usually explained by Faraday's Law in terms of changing magnetic fields cutting loops. Note that the Lorentz force is basically a defining equation for the magnetic field. This does not invalidate Faraday's Law. Faraday's Law is still obeyed always within the assumptions of classical physics. It has never been disproved; - not ever, and certainly not by your feeble logic.

The very title of this thread is an affront to the scientific method and seeks to do nothing but mislead the novice.

Note that it is important to use a proper form of Faraday's Law based on the situation. This can be done with the Tensor formulation of Maxwell's equations, or a proper general vector form of Faraday's law as follows:

$$\int (E+v \times B) \cdot dl=-\int {{dB}\over{dt}}\cdot ds$$
 bjacoby, You said that with the Faraday disk it is hard to make a case that the [free] electrons are dragged around with the disk as it turns. It is not hard at all, actually. In a typical current-carrying wire, the free electrons composing the drift current travel at a net speed of about a micron a second. If they did not travel around with the disk, they would constitute a tremendous current that would vaporized the disk with instantaneous heating. Mike
 elect_eng, You state that the operation of the Faraday disk is not based on Faraday's Law. That means that the basis of the operation of the Faraday disk is motional EMF and that motional EMF and Faraday's Law are independent. If they are independent, Faraday's Law cannot include motional EMF, which is what I have been maintaining all along. The equation you posted is exactly equivalent to what we have been referring to as Faraday's Law in this thread and is certainly false, as I have conclusively demonstrated throughout this thread. Mike

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