icester Posted September 10, 2018 Share Posted September 10, 2018 Hello, I have made an experiment based on mathematical model of EMF generated in segment of wire moving in constant velocity in uniform magnetic field: Here is the link to the mathematical model: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/genwir3.html#c1 My problem is that I am not getting any voltage out of wire at any speed up to 100 m/s. The field is 0.5 T and the wire length L is 0.02m... Please advice... Link to comment Share on other sites More sharing options...
quiet Posted September 10, 2018 Share Posted September 10, 2018 10 hours ago, icester said: I am not getting any voltage out of wire at any speed up to 100 m/s. The field is 0.5 T and the wire length L is 0.02m... Hi icester. I will run the risk of asking a question without knowing your preparation in physics. Have you studied, mathematically or conceptually, the properties of electromagnetic induction? If you have not studied them, we can talk a bit about it. Link to comment Share on other sites More sharing options...
studiot Posted September 10, 2018 Share Posted September 10, 2018 a speed of 100 metres per second! That's 225 miles per hour. How are you achieving this? Link to comment Share on other sites More sharing options...
icester Posted September 11, 2018 Author Share Posted September 11, 2018 Yes, I have studied all. I will post a picture of the experiment equipment in few hours. The magnet rotates up to 12000 rpm it is 101 mm diameter and 60 mm inner diameter... https://magnes.com.pl/duze-powyzej-20-mm/489--mp-101x60x4-1860578191932.html And the wire is 0.2mm diameter 20 mm long... I do not see how induction is possible in constant field and constant velocity but it looks consistent with Lorentz force phenomena... Link to comment Share on other sites More sharing options...
icester Posted September 11, 2018 Author Share Posted September 11, 2018 Here is my setup with rotating magnet a stationary wire connected to 1 mega ohm scope probe at 50 mV per division scale and there is 0 DC offset at maximum rpm of 10000 or less... Link to comment Share on other sites More sharing options...
quiet Posted September 11, 2018 Share Posted September 11, 2018 Have you tried another wire length? If thre is no error in your experimemt, then the case is very interesting. Link to comment Share on other sites More sharing options...
icester Posted September 11, 2018 Author Share Posted September 11, 2018 Yes, tried wires, coils but I have also noticed that it looks like Faraday's Paradox the case: when magnet rotates but disk is stationary... Maybe it only works with electrostatic voltmeter but at such low voltage (0.8V calculated using the formulae in the link) the only available instrument would be the non contact electrostatic low voltage/field meter which I do not have it yet... Link to comment Share on other sites More sharing options...
quiet Posted September 11, 2018 Share Posted September 11, 2018 Is disk magnetized? If it is, another question. Is a face of the disk one manetic pole and the other face the opposed pole? Link to comment Share on other sites More sharing options...
icester Posted September 11, 2018 Author Share Posted September 11, 2018 Yes, that is neodymium magnet 1 Tesla at the surface and direction of field is parallel to rotation access (visible face is one pole and back face is the other)... Link to comment Share on other sites More sharing options...
quiet Posted September 11, 2018 Share Posted September 11, 2018 (edited) Is the 2 cm wire placed at static position respect to the magnet? Edited September 11, 2018 by quiet Link to comment Share on other sites More sharing options...
icester Posted September 11, 2018 Author Share Posted September 11, 2018 (edited) Yes, magnet is rotating at 10000 rpm... If I make the magnet wobble then scope shows AC voltage but that is due to induction and not the Lorentz force... Also if such setup would work it would be better than Hall sensor since it does not require bias current... A College Text-Book of Physics_ 2nd Ed_ Arthur L Kimball_ 1917 also has such theoretical setup where 1m long wire moves at constant velocity cutting magnetic force lines of the Earth, but could not find a single experimental setup that would confirm such EMF voltage... Edited September 11, 2018 by icester Link to comment Share on other sites More sharing options...
quiet Posted September 11, 2018 Share Posted September 11, 2018 (edited) Let's go slowly. Let's look at the vector expression of Loretz's force. [math]F_{_L}= q \left( \vec{E} + \vec{v} \times \vec{B} \right)[/math] You know that the vector product is equal to zero when the vectors are parallel. And it is maximum when they are perpendicular. You only use a magnet. So the first term inside the parenthesis does not exist and remains [math]F_{_L}= q \ \vec{v} \times \vec{B}[/math] This means that the direction of wire movement can not be parallel to the direction of the magnetic field. The best condition is that they are perpendicular directions. --------- Outside of what was previously commented, what remains is conceptual understanding. In this phenomenon, the relative movement between the charge and the lines of the magnetic field is of interest. It is true that the description of the electromagnetic field devised by Faraday, in terms of field lines, is now considered obsolete. But for the concept that interests us I can not find a better description. From the questions you have answered, I understand that you have set up the experiment in the following way. 1. It is a magnet is a disk, with the poles on the sides of the disk. 2. The disk has uniform magnetization. Or at least, although it varies radially, it does not vary with the angular coordinate. 3. There is no relative movement between the disc axis and the 2 cm wire. The disk rotates but the axis remains fixed with respect to the wire. --------- With such an assembly, the wire sees no relative movement between itself and the magnetic field lines, regardless of whether the disk is rotating or still. Why ? Think of two contiguous circular sectors 1 and 2. When the disk rotates, the place that sector 1 leaves is occupied by sector 2. Both sectors are magnetically identical. Then the rotation of the disk does not cause a rearrangement of the lines of force of the magnetic field. The lines remain invariant, regardless of having the disk still, or spinning rapidly. The wire is still relative to the axis of the disk. Then it see invariant magnetic field lines, which remain motionless with respect to that wire. For that reason there is no potential difference between the ends of the wire, regardless of the angular velocity of the disk. --------- If you want to deepen the topic, you can ask the following. What would happen if instead of the oscilloscope you had an exquisitely sensitive instrument capable of measuring signals of atomic frequencies? In that case, when the disk rotates, the place left by an atom, an ion, a proton, an electron, can be occupied by a particle that is not magnetically identical to the previous one. Your esquisite instrument would react to the rearrangement of lines at the atomic scale and detect an irregular signal that, developed in a Fourier series, would have a fundamental component of atomic frequency. In other words, the spectrum of the signal would begin in that frequency order. --------- I hope I have understood the assembly well, otherwise the writing in this note is not valid. Edited September 11, 2018 by quiet Link to comment Share on other sites More sharing options...
icester Posted September 11, 2018 Author Share Posted September 11, 2018 Here is the magnet by itself : and from what I understood you claim that constant velocity motion of uniform magnetic field does not allow for induction in stationary conductor. If so then I agree but then what is going on with Lorentz force based EMF as claimed in mathematical model in : http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/genwir3.html#c1 Also I found this patent that has the same motion arrangement and it claims the same type of EMF: https://patents.google.com/patent/US5977684 Finaly I found this paper which is hard to understand for me but has links to many relevant devices and concepts : https://arxiv.org/pdf/1601.07750.pdf This study claims that brush less DC homopolar generators are not possible to construct: https://www.research.manchester.ac.uk/portal/files/54538050/FULL_TEXT.PDF Link to comment Share on other sites More sharing options...
quiet Posted September 11, 2018 Share Posted September 11, 2018 It seems an interesting topic. It also seems that I am completely uninformed about it. If you are not a member of the research group, have you tried to contact these people? Link to comment Share on other sites More sharing options...
icester Posted September 12, 2018 Author Share Posted September 12, 2018 No, I only just found the related material and the demo is just 3 days old... Also, after reading about Faraday's Law deficiencies at : https://arxiv.org/pdf/1601.07750.pdf I noticed that they have jumped the conclusion by assuming that homopolar generator works based on induction so to me it is not a credible volume of research... So, I am back with Lorentz and why the voltage is not observed as calculated by 100 year old mathematical model of trivial setup which is currently taught at universities around the World... Link to comment Share on other sites More sharing options...
icester Posted September 12, 2018 Author Share Posted September 12, 2018 (edited) This morning I decided to check the Homopolar DC Brush-less Generator Patent: https://patents.google.com/patent/US5977684 So I've made a toroidal coil with plastic bobbin and at 10000 rpm scope probe of 1Mohm 15pf connected to my HP 54602A scope again delivered 0 DC offset voltage at 50mV/division range... Since no existing brush-less Homopolar Generator physical device exist I conclude that the invention is a non-worker! Also according to the mathematical model at: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/genwir3.html#c1 There should be around 800v since there is 1000 turns on the toroidal coil... Next I shell write a letter to MIT since they are teaching student that there is an EMF at the output of wire segment moving in uniform magnetic field... http://web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide10.pdf Just found a video also reporting 0 EMF voltage: Edited September 12, 2018 by icester Link to comment Share on other sites More sharing options...
quiet Posted September 12, 2018 Share Posted September 12, 2018 If you think in cold way, is good idea to do more research before to say to university that something is wrong. Faraday, like you say, was the pioneer of homopolar generator. Tesla have introduced deep modifications, using a disk constituted by insulated partial pieces. I never have delivery time to study this issue. You did? Link to comment Share on other sites More sharing options...
icester Posted September 12, 2018 Author Share Posted September 12, 2018 No, if one asks for help to resolve the issue then it is nothing more than move in progress direction... Now my knowledge base has new practical experience and I can move on to design useful device with confidence... Thank you for helping... Link to comment Share on other sites More sharing options...
quiet Posted September 12, 2018 Share Posted September 12, 2018 Want you to be free with much energy? Link to comment Share on other sites More sharing options...
icester Posted September 12, 2018 Author Share Posted September 12, 2018 Sorry, I do not understand... Link to comment Share on other sites More sharing options...
Enthalpy Posted September 18, 2018 Share Posted September 18, 2018 You can't get a voltage with that setup. But that's tricky, as electromagnetism uses to be. Essentially, the moving magnet induces zero voltage in your closed loop as is. The setup nearest to yours is a homopolar generator, see Wiki. It has moving and immobile conductors, plus (uneasy) sliding electric contacts. More generally, it takes sliding contacts to produce a DC voltage from induction. A collector for instance. Link to comment Share on other sites More sharing options...
icester Posted September 30, 2018 Author Share Posted September 30, 2018 On 18.09.2018 at 10:18 PM, Enthalpy said: You can't get a voltage with that setup. But that's tricky, as electromagnetism uses to be. Essentially, the moving magnet induces zero voltage in your closed loop as is. The setup nearest to yours is a homopolar generator, see Wiki. It has moving and immobile conductors, plus (uneasy) sliding electric contacts. More generally, it takes sliding contacts to produce a DC voltage from induction. A collector for instance. There is no paradox and no induction (induction requires changes in magnetic field direction and or intensity)... Due to magnetic field copper disk experiences radial emf and brushes simply collect charges in both cases.. The emf is dynamic (rotation speed dependent) but based on static charge and radial path of the virtual conductor has very small amount of charge but faster the brush action more charges are collected thus emf potential is proportional to the brush rotation... The rule of Lorentz force defines the direction of EMF of the rotating virtual current path... Finally, Faraday's motor effect creates torque, thus no free energy generator possible... Induction works on neutral copper and Lorentz fores needs excess charge of one or the other sign... To produce detectable EMF... Link to comment Share on other sites More sharing options...
Enthalpy Posted October 11, 2018 Share Posted October 11, 2018 With a brush, a machine can work. That' a typical homopolar machine. But you show a measuring loop on the photo, completely static and without any sliding contact. This can't produce a DC voltage. Link to comment Share on other sites More sharing options...
Doug Jones Posted October 19, 2018 Share Posted October 19, 2018 You only have one magnetic field near coil. Try placing a coil of wire across the magnet edge near both sides (polls). Both fields must be used in order to induce voltage not just one I believe. Also voltage will be AC at the frequency of rotation not DC. You would have to rectify the output to get DC and the barrier potential of the diode is .65 volts so induced must be higher than that to get a DC meter reading on DC. Use a scope since all meters are calibrated to 60 cycle AC not 1000 cycles. Scopes only barrier to overcome to read is the bottom noise level. Link to comment Share on other sites More sharing options...
Strange Posted October 19, 2018 Share Posted October 19, 2018 28 minutes ago, Doug Jones said: polls poles Link to comment Share on other sites More sharing options...
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