The susceptivity of the material has absolutely negligible effect (unless the material is ferromagnetic which is not the case here).

However, conductivity is of direct, primary importance. For Lenz's law demos the actual value of the conductivity of the material is of primary importance. A material 100 times less conductive than copper is still a very good conductor by most standards, but the breaking force in it will be 100 times smaller. You should check the actual conductivity of your graphite tube material - you will no doubt find it much smaller than that of copper. Resistivity of graphite should be about 10 microOhm*m while that of copper is 0.017microOhm*m, which is a ratio of over 580. If so, the breaking force would be expected to be 580 times smaller in the graphite tube.

The wall thickness is also of utmost importance in this experiment, but you say that the tubes are identical, so we can rule that out.

Another thing: verify whether the graphite tube has good conductivity in the azimuthal direction ("around" the tube); it might be anisotropic and conduct better axially than azimuthally. Conductivity parallel to the axis is of no help in this experiment. For example, should you make a thin cut in the side of your copper tube, parallel to its axis, the breaking force would disappear totally.

Since the electric resistivities (the main influencers for eddy currents) of copper and carbon graphite differ by a factor of about 2000 one would expect that the copper pipe is much more effective in slowing down the falling magnet (compared with the graphite pipe) - just as the video tells us.

Btw, since aluminum conductivity is 1.67 times smaller that that of copper, the breaking force is 1,67 times smaller in aluminum tubes than in equal-shape copper tubes. Only silver is (very slightly) better than copper. Graphite is totally out of competition.

From https://www.thoughtco.com/table-of-electrical-resistivity-conductivity-608499:

Conductivity of Cu: 6 × 107 S/m

Conductivity of Al: 3.5 × 107

Conductivity of graphite: 2-3 × 105 parallel to easy plane, 3 ×102 normal to easy plane.

What was the puzzle again?

Dear emmanouil,

First of all let me to congratulate you for presenting these kind of experiments for everybody. The electric transport has been explained just taking into account that the graphite is a very bad conductor whereas the copper or aluminium are good conductors,i.e. they have a great number of free electrons above their Fermi level.

But your question goes a little bit further trying to involve the magnetic properties of these materials in the electric transport: Copper is a good diamagnet while Aluminium is a good paramagnet. In principle this relationship is quite negligable, but I would suggest you to extend the measurement in a more complex form just adding a circuit with a selfinduction L where you could try to measure the variation of the currents I under this change of mangnetic flux F

E=d/dt F- Ld/dt I

Where E is the induced electromotive force easily measured and the variation of magnetic flux too.

Daniel> I would suggest you to extend the measurement in a more complex form

Yess!! To really explore diamagnetism, you should try to repeat this experiment:

https://www.youtube.com/watch?v=A1vyB-O5i6E

It once lead to a Nobel prize; of the ignoble kind -- but one of the the prize winners later won the real prize!

Kåre Olaussen,

Each one suggests what he can and it is not necessary to write it in LATEX: your frog is delightfully following your experiment. Thanks!

Sorry, I have forgotten a minus in the Faraday's induction

E=-d/dt F- Ld/dt I

*Dear All,*

I contacted the creator of this video experiment and I've got the dimensions of the copper and carbon graphite pipes. L=7cm length for both tubes, Outer diameter bc= 1 cm for copper, bg= 1.3 cm for graphite. The graphite cylinder has a 3mm wall thickness and the copper a 1 mm thickness.

For copper pipe we calculate, with ρc = 0.0168 μΩ (see attached figures) :

Rcp (Copper pipe) = 78.8 μΩ.

For graphite pipe we calculate, with eddy currents perpendicular to the magnet's magnetic moment, thus eddy currents are travelling parallel to the basal plane of the graphite tube, therefore the average value for the special resistivity along the basal plane of graphite is given at ρg= 3.75 μΩ (see attached figures):

Rgp (Graphite pipe) = 4844 μΩ.

Therefore, we calculate approximately Rgp = 61X Rcp.

Thus copper pipe used in this experiment is 61 times more electrically conductive than the graphite pipe.

From the above, assuming all other variables in magnetic braking effect observed as negligible, I have extrapolated the the wall thickness of the graphite cylinder used in the experiment must be increased by a factor of x5 in order to observe the same magnetic braking effect as the copper tube used in the experiment.

Thus, if the initial graphite pipe wall thickness for example is 3 mm this must increased to 15 mm to observe the same amount of Lenz Law magnetic braking effect as the copper pipe.

The magnetic braking total delay effect for the copper pipe in this experiment results to a delay of approximately 1 sec the magnet to cross the pipe's length of 7 cm.

Diameter of the cylindrical magnet used in the experiment is a little less than a=1cm (be careful to use the radius values for the pipe and not the diameters in the calculations).

I don't have the means currently to replicate this experiment with a 15 mm wall thick graphite pipe to verify these calculations and conclusions. It would be nice if someone could replicate this experiment and report back here with the results.

The funny thing would be if despite the above, no magnetic braking will result on the graphite pipe!... then we are in trouble, and a publication is on... :)

Kind Regards,

Emmanouil

References

https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_and_conductivity_of_various_materials

Emmanouil Markoulakis > Thus, if the initial graphite pipe wall thickness for example is 3 mm this must increased to 15 mm to observe the same amount of Lenz Law magnetic breaking effect as the copper pipe.

You should be extremely careful making simple extrapolations without theoretical backing. It is not only a matter of getting the signs right in elementary formulas.

The breaking force is predicted to initially increase with conductivity (everything else being equal), reach a maximum, and then start decreasing. The breaking force is predicted to initially increase with magnet speed (everything else being equal), reach a maximum, and then start decreasing. This is due to screening/skin effect. The dependence on wall thickness is very unlikely to exhibit a linear behaviour, more likely a monotonous increase which reach saturation beyond a screen length. There is a fairly careful (hence complicated) analysis of this here:

Article Electrodynamics of a Magnet Moving through a Conducting Pipe

What I can't see treated in that paper is stability analysis. The real importance of having a diamagnetic tube is that this prevents the magnet from being attracted to the wall, and getting stuck. There is a discussion of this stability property by Michael Berry and André Geim, and why it is not in violation of the Earnshaw theorem. These were the people behind the levitating frog experiment I linked to above; for more about this amusing story see https://slate.com/business/2014/05/nobel-prize-in-physics-andre-geim-went-from-levitating-frogs-to-sciences-highest-honor.html

Dear Professor Baldomir,

Thank you for the suggestion. Here are the self inductance calculation results:

Lcp (Copper pipe) = -11.7 nH (μr = 0.999994)

Lgp (Graphite pipe) = -11.7 nH (μr = 0.9996) (approximately)

Area of the loop: 0.78 cm²

Number of turns of the loop: 1

Magnetic field: 0.2 T (assumed) Magnetic flux: 0.0000156 Wb (15.6 μWb)

Time: 1 sec

SelfInduced voltage (copper pipe) : - 0.0000156 V (15.6 μV)

I = 15.6/78.8= 198 nA. The self induced magnetic field (not the eddy current field) opposing the field of the permanent magnet would be

B(Self induced)= 0.00355447 nT

Similarly, the self induced voltage for the graphite pipe with an observed time estimated at 0.1 sec will result at - 156 μV and I=156/4844= 32.2 nA with B(self induced)= 0.000577822 nT.

Therefore the self induced B field in the copper pipe is x6.1 stronger than the graphite pipe.

Obviously this self induced forces are negligible to the total magnetic eddy currents breaking effect and easily overcome by gravity.

Dear Professor Kåre Olaussen,

I agree, that is why I included in my calculations the statement:

quote: "From the above, assuming all other variables in magnetic breaking effect observed as negligible..."

It is supposed to be a rough estimate to allow us to see some magnetic breaking effect with the graphite taking into account only the electric resistivity of the pipe.

Nevertheless, thank you for the information, references and inside you shared.

Kind Regards,

Emmanouil

Dear Emmanouil,

I know that these values are very small and I only suggested you the measured using a self inductance as a mean of seen what could be the Lenz currents if you could manage to design it. That is to say, my question is, could you put the conditions to distinguish the different physical magnitudes involved in the magnetic breaking? The difference between the diamagnetism and the paramagnetism is obviously very small and I suppose that its role on the transport is negligable, but I'm not sure. Could you find any form to distinguish what you have introduced in your thread? Notice that I am not restricting to the devise that you have at this moment but to a new one where you could add an electronic device amplificating the signals. This was my idea, but I understand very well that you don't do it.

Found this little gem:

https://www.youtube.com/watch?v=copZj1WF0Y8

What is your theory about the magnet's poles flipping inside the channel?

Emmanouil Markoulakis > What is your theory about the magnet's poles flipping

When the poles are oriented sideways it is obviously a stability effect. A difference between north-south pole oriented upwards is more difficult to explain; that ought to be equivalent due to symmetry. A couple of possible explanations: i) The Earth magnetic field breaks the symmetry; quantitative analysis is required to check if that leads to a sufficiently large difference (or one may check experimentally by comparing identical setups in say Europe and Australia/Antarctica), ii) Manufacturing asymmetries; if these are random the preferred pole should vary from magnet to magnet.

Dear All,

1) An important observation: About the graphite pipe experiment. Notice the possibility that the 1mm thick copper pipe used in this experiment not to be diamagnetic at all but actually paramagnetic (even higher than the aluminum pipe)

We notice that this copper pipe used is quite highly oxidized. From the bellow table:

https://www.reade.com/reade-resources/reference-educational/reade-reference-chart-particle-property-briefings/31-magnetic-properties-a-susceptibilities-chart

We can see that although copper element has a diamagnetic susceptibility of -5.46X10-6 cm3/mol, copper oxide is actually quite strong paramagnetic with susceptibility of +259.6X10-6 cm3/mol !! Even higher paramagnetic than aluminum element which has +16.5X10-6 cm3/mol and its aluminum oxide is actually diamagnetic at -37X10-6 cm3/mol.

This would also explain why all the experiments done with copper pipes are producing a magnetic breaking effect. It would be interesting to see how an unoxidised fresh made copper pipe would respond comparatively to an oxidized one, to determine quantitatively how the diamagnetic or paramagnetic property of a material affects the Lenz Law magnetic breaking effect.

Overall, at this stage of the discussion I'm not totally convinced that a strong diamagnetic material, pipe like graphite will ever demonstrate the Lenz Law magnetic breaking effect unless I see the experiment done with the thicker 15 mm graphite pipe.

I don't see how this is possible with diamagnetism of a material hindering EM induction which is a necessary for the generation of eddy currents and the Lenz Law.

2) About the sphere magnet flipping poles video. I believe it is because the open front side of the channel, this creates asymmetries in the generated eddy currents and therefore a torque is produced. The magnet flips immediately after it enters the channel. Its kinetic gravitational momentum created is enough to counter the initial magnetic dipole moment, so it flips. If the channel was longer I don't believe it would flip again. The magnetic dipole moment would eventually stabilize the magnet's fall.

Kind Regards,

Emmanouil

Dear Emmanouil,

There are only two stable copper oxides: Cu2O and CuO. The first is diamagnetic and only the last is paramagnetic (optically is easy to distinguish by its black color). Therefore it would be necessary to identify this component and let me to repeat that the influence of this magnetism is very small in the electric transport, in case that its influence would exist. I think that the simple device that you use is not enough and you are going to help with one external circuit the measurements to enhance their effect.

Again I repeat, my main arguments in this discussion here are:

Are strong diamagnetic materials immune to eddy currents Lenz Law, even if they are highly electrically conductive like silver for example?

and...

Is it possible, if magnetic breaking is finally observed in strong diamagnetic materials and very electrically conductive, like silver or cold for example, this to be attributed not to eddy currents Lenz Law but to diamagnetism of the material producing apparently the same magnetic breaking effect?

The magnetic breaking effect produced for example by a pure silver piece sliding through a very strong magnet slide ramp could easily explained also not by eddy currents but by diamagnetism alone repelling the silver piece all the time as it slides and not leaving it to free slide, thus the same apparent magnetic breaking effect will be produced:

https://www.youtube.com/watch?v=8gLB2uMAMYM

Unfortunately, in the above video the creator does not say how pure the silver pieces are, he is using.

There is however a fast way experiment to distinguish between eddy currents Lenz Law and diamagnetism. Since diamagnetism always repels an external magnetic field, but Lenz Law eddy currents opposes an external magnetic field, using the above principle, if you retract away very fast a strong magnet from an electric conductor materiel, then the material should be attracted by the magnet according to the Lenz Law and the eddy currents formed inside it.

But if an electrically conductive and diamagnetic material is immune to eddy currents Lenz Law, then the same fast magnet retraction movement should not cause any attraction effect at all since diamagnetism always repels an external magnetic field contrary to the Lenz Law magnetic effect, which can repel but also attract an external field relative to its motion and amplitude variation:

https://www.youtube.com/watch?v=Kink-XO4X1s

The above video is the only I could find that describes the above method. However, unfortunately again the creator of this video does not include any information about the purity of the silver he is using.

Also I'm not sure if this Lenz effect spring motion observed is purely due to magnetic Lenz Law and not due to the spring mechanical force produced by the elastic test surface he is using since he is initially pushing the magnet against it.

Emmanouil

p.s. This here is an excellent video series demonstrating the individual magnetic properties of the elements of the periodic table:

https://www.youtube.com/watch?v=I2pmV_jjC7c

Dear Emmanouil,

Let me try to answer your initial question:

Are strong diamagnetic materials immune to eddy currents Lenz Law, even if they are highly electrically conductive like silver for example?

No. This effects are independent. In Landau diamagnetism (for metals) what you have is one dependence with the paramagnetism.

Dear Professor Baldomir,

quote: "No. This effects are independent. In Landau diamagnetism (for metals) what you have is one dependence with the paramagnetism."

I agree. At least now after this investigation here, if copper is observed in some cases, to have a larger Lenz Law magnetic breaking effect than the more conductive silver when all calculations conclude that it shouldn't, we will know that this is possible because copper oxide CuO contribution, which turns the copper from being diamagnetic to relative strong (more than aluminium) paramagnetic! Specially for 1-2 mm or less thin layers of copper.

I don't know if a quantitative and qualitative analysis of this contribution to the overall magnetic breaking effect of copper compared to other conductors and free electrons Lenz Law magnetic breaking compared to paramagnetic breaking effect of oxidized copper will have any appeal to the science community and earning a publication?

Thank you for your precious inside and info shared.

Kind Regards,

Emmanouil Markoulakis

Technological Educational Institute of Crete

Done. :)

Preprint Paramagnetic braking effect contribution to the overall magn...

I am open to collaborations for this possible project.

The answer might be due to the amorphous nature of graphite versus the crystalline nature of metals. The statistical organization of back emf in graphite is net zero.

Michael,

That is why I need to see the 15 mm thick graphite experiment results. I will be very surprised if there is not any,

It has to be investigated the degree with which the static magnetic properties (i.e. diamagnetic, paramagnetic) of an electrical conductor contribute to the overall magnetic breaking phenomenon compared to the breaking due to the dynamic eddy currents.

Specially, with paramagnetic conductors which are usually more magnetically reactive in general than diamagnetic (i.e. paramagnetic materials attraction is stronger than diamagnetic materials repulsion to an external magnetic field).

Also notice that the static paramagnetic reaction of an material on a moving or variable external magnetic field or magnet in no way can be regarded as a static event but as a dynamic magnetic transient reaction which will will be many times stronger than the static. In other words, dynamic magnetism specially at short transient events (i.e. pulsed signals) produces a greater forces and attractive reaction.

This possibility can not be dismissed and must be investigated.

The first thing I will do is to compare to identical conductors for magnetic breaking with one of the two heavy oxidized.

I think the answer can be found in the granular structure of the sintered graphite. The small grains sizes (separated by thin insulating layers) do not allow the eddy currents to occur.

Dear I.G.Deac

I think this has been already accounted for in the calculations presented in this thread here by taking the parallel to the basal plane value of the special resistivity of carbon graphite reported to be ρg= 3.75 μΩm @20C in average.

reference: https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_and_conductivity_of_various_materials

The electrical conduction in granular materials and in bulk is very different. The eddy currents have a sort of circular paths. If the grain size is smaller than the diameter of these paths, the eddy current cannot form. See the cases of the cores of electrical transformers and of the copper bars used for adiabatic nuclear demagnetization. When you apply a dc voltage across this material, the electrical field is enough high and the electrical current can pass through the barrier between grains.

If that is true, then a pyrolytic graphite pipe of the same dimensions shown here with the normal graphite pipe would create a strong magnetic braking effect. I have to do this experiment.

Nice made video demonstrating paramgnetism and diamgnetism of various elements:

https://www.youtube.com/watch?v=u36QpPvEh2c

Lenz Magetic Braking explained:

https://www.youtube.com/watch?v=BIsKthqeKSo

Impressive and thorough video about Eddy currents testing:

https://www.youtube.com/watch?v=oriFJByl6Hs

THE GRAPHENE HAS ITS OWN PROPERTY DOFFERENT THEN OTHER METALS. CONDUCTIVITY IN GRAPHANE FOLLOW DIFFERENT FUNDAMENTL PRINCIPLE OF PHYSICS.

Dear Professor Dillip KUMAR Bisoyi ,

We are talking specifically about graphite not graphene.

Can you please elaborate more on your answer?

Are you referring to that atomic lattice structure of graphite may don't allow the formation of Eddy currents?

Kind Regards,

Emmanouil Markoulakis

Hellenic Mediterranean University

(prior Technological Educational Institute of Crete)

As you can see the eddy current formed in a graphite pipe by a falling magnet is parallel to the basal plane of the graphite therefore the special resistivity is reported to be ρg= 2.5 μΩ which is not that low as copper (about 20 times more resistiive) however a thick graphite pipe should produce eddy currents and therefore magnetic braking effect.

The questions here is, will say a 1cm thick graphite pipe exhibit any magnetic braking effect?