abhilash

Hello everyone, welcome Consider a straight long tube CD which on conduction electro-deposition of copper takes place at the cathode (-). The cathode is in contact with a long piece of wire AB (as shown in fig 3) which is connected to the negative terminal of the battery and the anode is connected to the positive terminal. PQRS is a piece of wire or a metal plate shaped as shown and is placed near this (AB – CD) arrangement. We all agree with relativity, its two postulates and we all agree with the effects of Lorentz contraction on things moving with respect to us. but why is the effect of Lorentz contraction on moving electrons in a wire often neglected ? Often this question is answered this way - well, we know the wire is not charged, so let’s not speak about Lorentz contraction here (and let's neglect the first postulate of relativity here). Another reason I have encountered is that electrons are considered as point charges, so again let’s not speak about Lorentz contraction here - (relativistic redistribution of electric field lines are possible even there and what about Lorentz contraction of the “lengths” between these points). Aren't’t these like saying “you can disregard relativity in-order to support relativity” or as I quoted in my first post “even though the laws of physics are the same for all inertial reference frames, we can have different laws of physics (for the same phenomenon) in the same inertial reference frame”. Now when you consider Lorentz contraction of moving electrons -if there is an increase in charge density of the moving electrons, shouldn't’t the wire acquire a net positive charge? Yes, they will attract positive charges from the outside of the wire.Then if we place a metal strip then it should repel the electrons to the other end of the strip and hence we should measure a potential difference across the strip ? No and the reasons why we can't directly measure its effect that (with reference to the figure)- 1) The electric field which acts on the metallic strip CD is also acting on the probes of the potentiometer (Fig 3) which develops the same potential across it (i.e., the probes of the wire that are equi-distant from the wire AB are at equi -potential and hence the potentiometer reads zero potential. This creates a situation where the voltage developed can’t be measured directly. Moreover, 2) The calculated potential developed in case 2) is generally of the order of Pico-volts (for a few amps) and this clubbed with the above fact (1) makes it even harder to detect this increase in charge density. If this is confusing, please see my orginal post where this is written in terms of force.of magnetic effect and please scroll down a bit until you see the above figure. This was the conditions outside of the wire. Now, will the increased charge density of the conducting electrons draw more (+) charges from a possible reservoir (earth) along the length of the wire? There can’t be any effect to due to increase in charge density of the electrons inside the wire, because this is offseted by the redistribution of the electric lines of force of the moving charges as shown in the figure and hence it will not draw opposite charges from the reservoir . (This answer is only partly answered here and I am not quite satisfied with this explanation since there has to be other effects of relativity in this –but this kind of reasoning has the decency that it does not disregard the theory of relativity in order to support it). Now,would you please answer this question - would there be a potential developed across PS in the first figure ? Thank you.

Ok, but what about the distance or length between those point charges? Shouldn’t they contract too effectively increasing charge density of the electrons? Thank you Swansont.

Thank you Swansont for yor reply and sorry for the delay. is this what you meant with your reply? in case 1 - there is a magnetic field , there is no electric force and there is no magnetic force. and in case 2, where there is a relative velocity between the long wire and CD, there are two cases. a) for an observer who is at rest with respect to the wire sees a magnetic force, Fm. and B) for an observer who is moving along with the electrons in the wire, there will be an Electric force , Em such that Em = Fm. my question is 1) in case 1) of course the wire is neutral, but why isnt there any lorentz-contraction taking place, After all the electrons are moving? thank you.

Thank you Swansont for your reply. what is the cause of the magnetic field in - case 1 - where the electrons are at motion with respect to Q and case2 - where the net nuclear positive charge is moving. Since the second part of the previous post is not connected to the orginal post I am re-posting this. sorry if this troubled you. thank you.

Ok and thank you swansant for replying to me. Let me modify case 1 and case 2 as two different (sets) in a single system. Here CD is in between AB and XY as shown in the fig-a. AB is stationary with respect to CD and a current is flowing in AB as shown. CD is at rest with respect to the non-conducting charges in AB and the conducting electrons in AB are moving with a positive velocity Vd. However with XY, the potential across XY is reversed to that of AB causing the electrons in XY to move with a negative drift velocity, and at that very instant, XY starts to move with a positive drift velocity. (please see it this way, at the very instant the electrons in XY starts to move with an incrementally small negative velocity, XY also starts to move with an equally but positive incremental velocity). So essentially, CD is at rest with respect to conducting electrons in XY while it is moving with respect to non conducting charges in XY). So in this frame with respect to CD, exactly identical conditions exist, CD is at rest with respect to one kind of charge and is in motion with respect to the opposite kind of (net) charge and there is just one frame of reference which is at rest with respect to Q. But in set {AB-CD} system*, there is NO force where as in set {XY-CD} system there is. This is the anomaly, two different results for a similar or same cause. * with this it only means that current in conductor XY has no magnetic or any other effect on CD in set{AB-CD} system which is in fact a subset of set{AB-CD-XY} system and is equivalent to case 1. Moreover, saying that there isn’t a potential developed in one and on the other there is like saying -even though the laws of physics are the same for all inertial reference frames, we can have different laws of physics (for the same phenomenon) in the same inertial reference frame. In another thought experiment, consider a straight long wire, a portion of which is wound around a freely rotating pulley-wheel (so that this arrangement can move along the length of the wire –rotating, winding on one side and unwinding at the other as it is dragged) and this in turn forms the coil of a galvanometer which can deflect a magnetic needle). Fig b. Now consider, a long current carrying wire MN which is connected to two such galvanometers G and H in series and these can move along the length of the wire as shown in the fig b. consider two observers GO and HO each with a watch. GO is at rest with respect to the conductor MN and G . Observer HO and H is moving along with the conducting electrons in MN. So, when asked to measure their time, GO will look at his watch and denote his time. Similarly, HO too will look at his watch which his moving along with him and tells the time which of course agrees with relativity. Now if GO is asked to measure the current and find the cause of the magnetic field, GO will observe it rightfully with the help of G which is in his frame of reference and deciphers that the magnetic field is caused by the flow of electrons. However if this question is asked to HO, HO instead of looking at H, HO will look at G measures the current and says that magnetic field is caused by the flow of electrons. It is equivalent to HO looking at G’s watch and calling out G’s time. Instead, shouldn’t it be like this- HO should look at H, and measure the current (which is of course has the same magnitude as in G but because of a different reason). H Should notice that the current is caused by the flow of net positive charge and decipher that this is the cause of the magnetic field. Since for H and HO, conducting electrons are at rest and it will not cause a time-variance in electric field. And hence no magnetic field is caused by those electrons. After all we all know that it only charge of the nucleus (just like electronic charge) that we should be concerned with in these scenarios. Why should we give more preference to one of the type of charges over the other just because nucleus makes the bulk of the material? Moreover we often comes to the situation where (if we group the charges of a conductor into two (+) and (-) groups), with respect to an observer, motion of one type of charge group produce a magnetic field while the motion of the other type of charge group doesn’t (and its vice versa where a stationary charge which is not producing any time-variance in its electric field produces a magnetic field). Aren’t these examples for “different laws of physics (for the same phenomenon) in the same inertial reference frame”. (let me stress again that, I do not have any intentions to argue against the theory of relativity. I do believe it’s accurate prediction of various things , from Lorentz contraction to relating energy to mass, to time dilation etc is possible only because it is true and because of this I do believe that Michelson-Morley experiment is interpreted in the right way itself). It’s only against the concept of magnetism that I am arguing with and if this is to change anything regarding relativity, it will be just a few mis-concepts regarding the theory of relativity. The reason for saying that is this, even though theory of relativity wasn’t written with this concept of magnetism in mind, the basic underlying concepts, reasoning and the mathematics associated with it holds true. Thank you Farsight for your reply Farsight in fig3, the current is flowing from positive to neagtive and it is the direction of the current that I have shown in both AB and CD section, ofcouse electrons flow in the opposite direction in AB. If you still see a problem with this do please reply. And regarding the experiment, I just thought of more practical one. either should equally suffice. and there is a bit more in today's post and I dont know how much you will agree with this. Anyway I am waiting for your reply. Thanks Pardon me for my possible typing errors in this but do please bring it into my notice so that not only it will help me in eliminating these errors, but also others who are in a way into this post. Thanking you.

THANKS a lot Farsight for your reply and especially for remarking it as “Interesting” for this article was often misleadingly interpreted (by almost everyone) as something that was against the well established theory of relativity in majority of the newsgroups and hence ridiculed. And I do completely agree with your comments regarding the facts 1) and 2). The purpose I added these four (incomplete) facts was because of the experience I had got from other newsgroups and believing that this should help me in expressing my viewpoint. Since this article wasn’t concerned with displacement current and since I wanted this article to be as concise as possible, I didn’t give much relevance to it which I should have. (Your comment definitely fills this gap –thank you). Similarly is the case with expressing fact 2)- I do agree with your opinion regarding this context sensitive “producing or creating” magnetic field terminology and even now I am running out of words (perhaps its because its late night two now). And thankyou for referring me to Jefimenko's equations and the abstract is really interesting since it’s my pleasure to be with these kinds of stuff especially regarding induction on which I wish to write an article. Thank you.

This article is an abridged version of the original article posted in google groups. For further proofs or clarifications please download the file titled electrodynamics and magnetism.pdf from the link that is given at the last part of this article. As a preface – this experiment is based on these well established facts that 1) Current is the rate of flow of charge – any charge, not just the flow of electrons. 2) This flow of charge produces a magnetic field around itself/conductor. 3) Classical physics is purely deterministic and that definite causes should have definite results. 4) Observers in the same frame of reference (and who are at the same point and stationary to each other) should agree with same or similar incidents (ie, all parameters remaining the same). Before coming to the experiment, the reasons for this experiment are explained otherwise its necessity would not be appreciated. THE ANOMALY:- Consider the setup - AB is an infinitely long current carrying conductor carrying current I. let CD be a metal strip positioned near to the conductor. Case 1) The conductor AB is at rest with respect to the metal strip CD (fig 1A) Here there will be a magnetic field in and around the metal strip CD, but there won’t be any potential developed across it (since there is no magnetic force acting on the electrons in CD). Case 2) the potential applied to AB is reversed (so drift velocity is negative), and CD is moving with a negative drift velocity– i.e., here essentially CD is at rest with the conducting electrons in AB and moving with respect to non conducting charges. Here, there will be a magnetic field and there will be magnetic force acting on the conducting electrons of the metallic strip CD. This causes a potential to be developed across CD. Now, it can be seen that in both cases the metal strip is under exactly similar conditions as shown in Fig 2- CD is stationary with respect to one kind of charges in AB and is moving with respect to the other (opposite) kind of charge. In case1) the metallic strip CD sees a current due to the flow of electrons in the conductor AB and in case 2) the metallic strip CD sees a current due to the (net) flow of nuclear positive charge in conductor AB. In case1) the flowing electrons in AB produce a magnetic field. In case2) it is the net nuclear positive charge that is moving. Shouldn’t they produce a magnetic field? However it is well known fact that the potential developed in the two cases are different. Now if one observes closely, this anomaly of measuring different potential under identical situation can be easily explained. 1) The magnetic field which acts on the metallic strip CD is also acting on the probes of the potentiometer (Fig 2B) which develops the same potential across it (i.e., the probes of the wire that are equi-distant from the wire AB are at equi -potential and hence the potentiometer reads zero potential. This creates a situation where the voltage developed can’t be measured directly. 2) The calculated potential developed in case 2) is generally of the order of Pico-volts (for a few amps) and this clubbed with the above fact (1) makes it even harder to detect. Assuming it is due to these reasons that the measured potential was different, one can straightforwardly come to the conclusion that the force (in this case and at “atomic” level) acting on the electrons in CD has to be of the form – F=k q Q V^2/r (force in case 2 which has to be true in case 1 also)* Where k = a constant, q = charge of the electrons (in CD), Q = concerned conducting Charge in AB, V = drift velocity of electrons (relative velocity between the charges in motion). (* it can be seen seen that at the “macroscopic” level this still retains the equation for net force as F= Bqv which is independent of the relative velocity of the moving charges and is described in the orginal version of this article and it's link is given at the final part of this article). (It should be noted that force between charges in motion are not always related to square of their relative velocities, which is mentioned in the later part of this article**). What was said above can be easily proved with the help of an experiment as described below. THE EXPERIMENT:- (This experiment is based on above equation that this force on the electrons is proportional to square of the relative velocity and sign of the concerned charges. So materials with different drift velocity (or with different current carriers) should exert different force on charges placed near to them). Consider a straight long tube CD which on conduction electro-deposition of copper takes place at the cathode (-). The cathode is in contact with a long piece of wire AB (as shown in fig 3) which is connected to the negative terminal of the battery and the anode is connected to the positive terminal. PQRS is a piece of wire or a metal plate shaped as shown and is placed near this (AB – CD) arrangement. On the tube, the carriers of current are the positive ions where as in the wire; it is the electrons that conduct electricity. On conduction (as per the equation-given above), the conducting electrons in AB repel electrons in PQRS away from it whereas the moving cat ions on the tube attract electrons towards it. This causes a potential to be developed in PQRS and can be measured directly. (Here the length of QP/RS has to be much smaller than the length of AB and CD preferably QP=1cm and QR= 200cm). In the above experiment, in place of AB and CD, n-type and P-type semiconductors can be used which should develop much more voltage across PS (of the order of nano-volts) since the drift velocity of electrons in semiconductors is much greater. So the question is –would there be a potential developed across P-S? ======================================================== ** Consider a straight long wire AB carrying current I and a charge Q is moving perpendicular to it with a velocity V as shown in the figure 4. Here as the particle moves, it can be seen that its “r”, the distance between AB and Q that varies and hence the magnitude of the magnetic field changes and thus, it is magnetic induction that plays here and is very different from the above case. V = dr/dt Here clearly the equation for the force take the form F= BQV which is independent of the square of their relative velocities. For a detailed description about this article please download the file titled Electrodynamics and Magnetism.pdf from the site http://groups.google.com/group/electrodynamicsandmagnetism Please see this experiment as a classical one since I prefer a rational and logical answer thats in agreement with the four facts that was quoted at the beginning of this article. Additionally, I request you to see me as a person who believes in the theory of relativity and sees it with great awe and respect. (If you wish to chat with me regarding the content of this article, please reply to me with your expected/preferred time (in GMT) so that we can share our views). Many thanks in advance Abhilash j pillai.