Does a magnetic field rotate with a magnet...the answer!
in [Physics]
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From: BURT on 2 Mar 2010 01:36 On Mar 1, 9:54 pm, Salmon Egg <Salmon...(a)sbcglobal.net> wrote: > In article <tF_in.301043$8K4.182...(a)newsfe15.ams2>, > > "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > > > And if you do that you find that currents are a source. They create > > magnetic fields and they also create electric fields (which is called > > induction). Since they create both things at once people often jump to > > a mistaken conclusion that magnetic fields cause E fields and vice > > versa. > > If you want to be accurate and precise, current is a source of VECTOR > POTENTIAL. To find the magnetic field you use the current distribution > subject to boundary conditions to calculate the vector potential. Take > the curl of this potential to get the B field. > > Now if you do use vector potentials, how does the vector potential from > the equivalent surface currents of a cylindrically symmetric bar magnet > change the vector potential as it is spun about its axis? > > Maybe I should entitle this blurb with: Does the vector potential of a > spinning magnet produce a variable vector potential? > > Bill > > -- > An old man would be better off never having been born. Maybe you're not as smart as you look? Mitch Raemsch
From: Benj on 2 Mar 2010 01:56 On Mar 2, 12:54 am, Salmon Egg <Salmon...(a)sbcglobal.net> wrote: > If you want to be accurate and precise, current is a source of VECTOR > POTENTIAL. To find the magnetic field you use the current distribution > subject to boundary conditions to calculate the vector potential. Take > the curl of this potential to get the B field. Yes, a current IS a source of Vector Potential. However A is NOT the source of the magnetic field OR the induced E field. You can see that because the Vector Potential, A, is retarded as is the magnetic field at the point of the induced E field. Hence since E, B, and A all happen at the same time, one cannot cause one of the others by the rules of causality! Now if you take the curl of A you do indeed get that VALUE of B but it only says the two quantities have a relationship not that A causes B! > Now if you do use vector potentials, how does the vector potential from > the equivalent surface currents of a cylindrically symmetric bar magnet > change the vector potential as it is spun about its axis? Good question! I don't know the answer, but I do know what you'd have to do. First you'd have to find the magnetic vector potential for points outside a neutral current moving in or opposite to its direction of flow at a constant velocity V. We already know that a neutral current moving at constant velocity in the direction of flow creates not only an induction E field but also an ordinary electrostatic E field because of the motion. For the E field we know that since it's a neutral current we expect no electrostatic E field due to the charges. But we can show that what we find is an induced E field whose value is equal to v x B at the E field observation point. Thus if we want to examine the B field there we have to note that the B field measured outside a moving neutral current is changed by the relationship H*=H - v x D. Thus we find that the B field there is reduced according to the E field induced (E is related to D in free space) and the velocity! That obviously will be identically reflected in our calculation of A! Hence we note that A indeed must also be affected when a neutral current is made to move at a constant velocity in its direction of flow. Thus we can see that if you spin a current (solenoid or equivalently a permanent magnet) on it's axis the velocity will indeed show up in all three quantities: E, B, and A! Interesting stuff that few people seem to have bothered to calculate! In fact that seems to be the problem. Everybody knows that retardation is the proper way to calculating Maxwell's equations to get the correct answers, but the calculations with delays introduced are bears. And it seems that very few people (with a couple of exceptions) have had the grit to dig in and try to actually see what is going on! > Maybe I should entitle this blurb with: Does the vector potential of a > spinning magnet produce a variable vector potential? Good point. Since a moving current element creates E, B, and A the question is therefore clearly what does a spinning magnet do with regard to each of these. So far we have asserted that a spinning current loop induces an E field in nearby conductors (Faraday Generator) And we do know that the B field is also present, even though we haven't yet figured out if it actually rotates or not. (Whatever that might mean) And likewise we see that A is generated by the moving current loop and modulated by it's velocity. And even though we haven't calculated A we do know it's related to B so finding what A does just may give us a hint as to what B is doing!
From: Vince Morgan on 2 Mar 2010 03:27 "Benj" <bjacoby(a)iwaynet.net> wrote in message news:cac97edc-1745-4d16-bad6-b4ff27456d38(a)v20g2000yqv.googlegroups.com... On Mar 1, 3:18 am, "Vince Morgan" <vin...(a)TAKEOUToptusnet.com.au> wrote: > IDIOCY! My appologies. > I'll try again. > Could it be that Lorentz force, being directional, is what we have percieved > as magnetic dipoles? It pushes at one end and sucks on the other, so to > speak. I can see the Lorentze force dong this. And I see the accumulation > of many Lorentz force vectors making one larger, errrr, magnetic field. > I mean, if there is no unique entity as a 'magnetic filed' then any magnetic > dipole (All 'magnetic fields' are an aggragate of 'magnetic dipoles' aren't > they?) is simply the same phenomena. Ie. Lorentz interactions. > Wrong? > Highest regards, > Vince [quote] I'm not saying there is no such thing as a magnetic field! At least I don't think I am. What we are doing is trying to see what causes what! And if you do that you find that currents are a source. They create magnetic fields and they also create electric fields (which is called induction). Since they create both things at once people often jump to a mistaken conclusion that magnetic fields cause E fields and vice versa. The truth is that their VALUES are related to each other because they both come from the same source. But if we have a ring of current it creates a magnetic field. And if the ring is small and you look at the shape of the field it makes, it's exactly the same analog to the electric field made by a close-spaced + and - charge. In other words its a "dipole" field. Since all permanent magnets seem to be made as a result of currents (electrons) circulating around atoms, we see that magnetic dipoles are the source of that magnetism. I suppose since all magnetic fields come from currents and currents require that the circuit form a loop one might argue that all magnetic fields are dipole fields (at least at a large distance). But the magnetic field close to a straight wire isn't in the shape of a dipole field. [/quote] Well, I was being very lazy I have to admit. The thought of eliminating magnetic fields as an 'entity' was, well, silly. I'll just keep reading as this subject progresses, and re emerges from time to time, and hope it soaks in eventualy. If only it were as simple as I tried to make it :) Thank you, Vince
From: bert on 2 Mar 2010 18:07 On Feb 25, 6:15 pm, bert <herbertglazie...(a)msn.com> wrote: > On Feb 23, 8:44 pm, Salmon Egg <Salmon...(a)sbcglobal.net> wrote: > > > > > > > In article > > <050688a2-85ed-44db-b8a3-98a0e46e5...(a)h17g2000vbd.googlegroups.com>, > > > bert <herbertglazie...(a)msn.com> wrote: > > > Field flows from south pole to north pole,and is in constant motion. > > > This is shown to us by its "lines of force" (compass) Turn > > > mechanically an iron rotor into this field and pickup electrons and > > > you have a generator. Have electrons enter this field and the iron > > > rotor will turn,and you hhave an electric motor.Thus you see how both > > > are the same. Two sides to the same coin. Both just hum,as they > > > receive or transfer energy in the nicest way. Just one moving > > > part. TreBert > > > Field flows? How can such flow be demonstrated? Can fllowkng field be > > accumulated in a reservoir? > > > Bill > > > -- > > An old man would be better off never having been born. > > Bill No electric field can not be stored. It has to be keeped flowing. > Charge can be built up(like lighning) Electricity will not flow > unless it has a conducter.(copper wire) Magnetizim and electricity > two sides to same coin. Antenna and transmeter Two sides to the same > coin. Best to store magnets north and south. TreBert- Hide quoted text - > > - Show quoted text - Electric wire has a rotating field around it. I think it rotates clock wise. A looped (coil) wire has magnetic poles on each end I think the bottom part has the field goingcounter clock wise and top of coil clock wise Just think of all the coiled wire the LHC has. Some of it is splicedOi vay TreBert
From: Szczepan Bialek on 3 Mar 2010 04:42
"bert" <herbertglazier79(a)msn.com> wrote news:fcc91712-6f8b-4447-b711-7c87a01f6bd8(a)15g2000yqa.googlegroups.com... On Feb 25, 6:15 pm, bert <herbertglazie...(a)msn.com> wrote: > On Feb 23, 8:44 pm, Salmon Egg <Salmon...(a)sbcglobal.net> wrote: > > > In article > > <050688a2-85ed-44db-b8a3-98a0e46e5...(a)h17g2000vbd.googlegroups.com>, > >> > bert <herbertglazie...(a)msn.com> wrote: > > > Field flows from south pole to north pole,and is in constant motion. > > > This is shown to us by its "lines of force" (compass) Turn > > > mechanically an iron rotor into this field and pickup electrons and > > > you have a generator. Have electrons enter this field and the iron > > > rotor will turn,and you hhave an electric motor.Thus you see how both > > > are the same. Two sides to the same coin. Both just hum,as they > > > receive or transfer energy in the nicest way. Just one moving > > > part. TreBert > >> > Field flows? How can such flow be demonstrated? Can fllowkng field be > > accumulated in a reservoir? > >> Bill No electric field can not be stored. It has to be keeped flowing. > Charge can be built up(like lighning) Electricity will not flow > unless it has a conducter.(copper wire) Magnetizim and electricity > two sides to same coin. Antenna and transmeter Two sides to the same > coin. Best to store magnets north and south. TreBert- Hide quoted text - > > - Show quoted text - > Electric wire has a rotating field around it. I think it rotates clock wise. J. C. Maxwell wrote: "The mechanical conditions of a medium under magnetic influence have been variously conceived of, as currents, undulations, or states of displacement or strain, or of pressure or stress." From: http://en.wikisource.org/wiki/On_Physical_Lines_of_Force Rotating field is a flow (currents). It was Maxwell's choose. Kelvin chose strain and stresses: "In the Cambridge and Dublin Mathematical Journal for January 1847, Professor William Thomson has given a " Mecha- nical Representation of Electric, Magnetic, and Galvanic Forces,^' by means of the displacements of the particles of an elastic solid in a state of strain." Who is right? Kelvin or Maxwell? >A looped (coil) wire has magnetic poles on each end I think the bottom part has the field going counter clock wise and top of coil clock wise Just think of all the coiled wire the LHC has. Some of it is splicedOi vay TreBert What the state of strain is there? S* |