Does a magnetic field rotate with a magnet...the answer!
in [Physics]
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From: Darwin123 on 23 Feb 2010 12:50 On Feb 23, 4:35 am, Benj <bjac...(a)iwaynet.net> wrote: > On Feb 23, 3:46 am, "Cwatters" > > <colin.wattersNOS...(a)TurnersOakNOSPAM.plus.com> wrote: > > "Benj" <bjac...(a)iwaynet.net> wrote in message > > >news:201803fa-a4f9-437b-9a55-9294a391e8de(a)q29g2000yqn.googlegroups.com.... > > Perhaps you can explain why the power handling capability of a transformer > > core depends on it's volume.. > > That would be because saturation of magnetic materials is a material > property. > Any more questions? Why does the inductance of an air filled solenoid increase with volume? Why does the inductance of a vacuum filled solenoid increase with volume?
From: Darwin123 on 23 Feb 2010 12:55 On Feb 23, 4:35 am, Benj <bjac...(a)iwaynet.net> wrote: > On Feb 23, 3:46 am, "Cwatters" > > <colin.wattersNOS...(a)TurnersOakNOSPAM.plus.com> wrote: > > "Benj" <bjac...(a)iwaynet.net> wrote in message > > >news:201803fa-a4f9-437b-9a55-9294a391e8de(a)q29g2000yqn.googlegroups.com.... > > > As far as is known ALL magnetic fields come from currents. A permanent > > > > magnet can be seen to be a set of currents flowing around atoms. These > > > circular currents cancel where they touch throughout the body of the > > > magnet. They don't cancel on the outer surface. > > > Perhaps you can explain why the power handling capability of a transformer > > core depends on it's volume.. > > That would be because saturation of magnetic materials is a material > property. > Any more questions? 1) How come the inductance of a solenoid made of copper wires and filled with vacuum increase with volume? 2) How does an antennae, with no magnetic materials, manage to generate electromagnetic waves? 3) How come the electric field and the magnetic field are perpendicular in a collimated electromagnetic wave in a vacuum?
From: Benj on 23 Feb 2010 17:39 On Feb 23, 12:55 pm, Darwin123 <drosen0...(a)yahoo.com> wrote: > On Feb 23, 4:35 am, Benj <bjac...(a)iwaynet.net> wrote: > > That would be because saturation of magnetic materials is a material > > property. > > Any more questions? > > 1) How come the inductance of a solenoid made of copper wires and > filled with vacuum increase with volume? The inductance of ANY conductor in space is determined by it's geometry which is to say the way the path of the current goes through it. One could also ask why does a straight wire bent into a circle increase the inductance? The answer is each current element in the wire induces an E field in all the rest. If you move them closer they couple tighter and hence create more inductance. On the other hand if you have a solenoid of a certain size and make it twice the diameter it takes twice as much wire. Also if you make it twice as long it takes twice the wire. Hence there are twice as many current "elements" coupling to each other. > 2) How does an antennae, with no magnetic materials, manage to > generate electromagnetic waves? Um, that would be antennas (antennae are on bugs). The reason is totally straight-forward. Electromagnetic waves are created by CURRENTS. Electric and magnetic fields DO NOT create each other. Charges and currents are the source for BOTH! Which now creates an even more interesting question: How do antennas made out of nonconducting dielectric materials create EM radiation? > 3) How come the electric field and the magnetic field are > perpendicular in a collimated electromagnetic wave in a vacuum? I presume that the quick answer is that those are the directions that their source (currents) created them both. And then they propagate out into space at the speed of light. I'm not sure what you mean by "collimated" wave. Something like a TEM single mode laser perhaps?
From: Bill Miller on 23 Feb 2010 17:56 "Benj" <bjacoby(a)iwaynet.net> wrote in message news:201803fa-a4f9-437b-9a55-9294a391e8de(a)q29g2000yqn.googlegroups.com... > From the time of Faraday the question has remained "does a magnetic > field rotate with a rotating magnet? Rotate a cylindrical magnet on > it's axis and the question is does the field move with the magnet? In > other words in qV x B is relative motion between the test charge q and > the "postion" of the magnetic field B (whatever that means)? > > The answer it seems (like so many correct ideas that expose the lax > thinking of modern physics) is found in Jefimenko. In this case in his > book on causality and electromagnetic induction. The answer is ... it > doesn' matter! > > Jefimenko clearly derives the causality conditions for electric and > magnetic fields. Electric and magnetic fields clearly DO NOT create > each other. Faraday "magnetic induction" has NOTHING to do with a > magnetic field! A changing magnetic field does NOT induce a current or > voltage in a conductor! And even worse, the magnetic field related to > a moving magnet does NOT create the vxB Lorentz forces. This is strong > stuff. > > Instead what happens is that it is a current and it's variations that > creates the E field about itself in space. And further more it is a > current moving at constant velocity in the direction of it's flow that > not only creates an induced E field but a static "ordinary" one as > well. The VALUE of the combination of these two E fields is given by > VxB. > > As far as is known ALL magnetic fields come from currents. A permanent > magnet can be seen to be a set of currents flowing around atoms. These > circular currents cancel where they touch throughout the body of the > magnet. They don't cancel on the outer surface. Hence the equivalence > between say a cylindrical magnet and a current-carrying solenoid. Both > represent current flow around the outside of the cylinder. > > Hence in a Faraday generator, if one wants to know the relative motion > between parts it relates to the motion between the circular currents > of the permanent magnet and the rest of the apparatus. The relative > motions that count are between the magnet BODY and the Disk and wires > of the rest of the generator. The magnetic field is actually > irrelevant and it doesn't matter what it does! > > Jefimenko does it again! > > Hi Benj... Nice job. I *knew* you'd get it as soon as you discarded what you were taught and started applying what you'd learned! Bill
From: Bill Miller on 23 Feb 2010 18:09
"Benj" <bjacoby(a)iwaynet.net> wrote in message news:6846ec57-658a-4f2b-9858-b347239faf19(a)z35g2000yqd.googlegroups.com... On Feb 23, 12:55 pm, Darwin123 <drosen0...(a)yahoo.com> wrote: > On Feb 23, 4:35 am, Benj <bjac...(a)iwaynet.net> wrote: <snip> > 2) How does an antennae, with no magnetic materials, manage to > generate electromagnetic waves? Um, that would be antennas (antennae are on bugs). The reason is totally straight-forward. Electromagnetic waves are created by CURRENTS. Electric and magnetic fields DO NOT create each other. Charges and currents are the source for BOTH! Which now creates an even more interesting question: How do antennas made out of nonconducting dielectric materials create EM radiation? BONG! BONG! BONG! This is a common mis-perception. An antenna does not create EM radiation. I "guides it." The actual generation of the EM wave occurs where electrons are accelerated. This may be as electrons flow between a cathode to the anode of a vacuum tube, across the gap in a klystron, or in the "innards" of a sold state device -- to name just a few sources. Once the EM signal is "made" it is then guided by a transmission line that is specifically designed to *inhibit* radiation. Once the energy reaches the antenna, the EM energy will radiate in accordance with the antenna's inherent characteristics. It is interesting to calculate and view the "streamlines" of the Poynting Vector as they flow through the transmission line to the antenna and thence outward. They are unbroken from the source to as far out as you care to plot them. Bill Miller <snip> |