Does a magnetic field rotate with a magnet...the answer!
in [Physics]
|
From: Salmon Egg on 23 Feb 2010 20:44 In article <050688a2-85ed-44db-b8a3-98a0e46e57d8(a)h17g2000vbd.googlegroups.com>, bert <herbertglazier79(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.
From: Benj on 24 Feb 2010 00:06 On Feb 23, 6:09 pm, "Bill Miller" <billmillerkt...(a)worldnet.att.net> wrote: > 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. I know what your are saying but I'm not sure I "buy" it. It's certain that power in a DC sense changes to RF in a tube or klystron etc. and it's also certain that the resulting currents of that tube also create RF fields that are guided from it to an antenna and into space. But my point would be that from the tube to an antenna the power is in fact a DUAL entity. There are CURRENTS flowing in the transmission line and antenna as well as fields about or within those entities. And time- changing currents are the source for the electric and magnetic fields measured by the Poynting vector. Hence there is something of a quandary there in that one can consider the power in the current or the power in the fields. HOWEVER, beyond the surface of the antenna that changes. Beyond the antenna there are no currents in space. Hence we see two critical "turning" points in our transmitter. One is at the tube where DC power changes to high frequency power and another at the antenna where actual currents are left behind and pure fields are propagated onward! This then leaves a question. Are the fields of the transmission line propagating on the antenna and then launched into space or do the currents from the transmission line create an excitation of a resonant "circuit" which is the conductive antenna structure of which the currents flowing upon that structure are the source (charges and currents are the ONLY sources for EM fields) for the EM fields launched into space. I suggest that in the case of many antennas of the classic kind (dipoles etc) it is the latter. Of course as I intimated above, the other situation can also occur. This is when fields from the transmitter are guided to dielectric antennas where they are then guided into space. These are called "traveling wave antennas". The fact that charges and currents are the source of E and H fields makes things like transmission lines and antennas where both fields and currents are present an interesting case. It's sort of like arguing which is the more "fundamental" field, A or B. Since changing currents are the cause of fields, I argue that current is the fundamental quantity. That's my assessment.
From: Szczepan Białek on 24 Feb 2010 12:29 "Bill Miller" <billmillerkt4ye(a)worldnet.att.net>wrote news:7uj5baFagaU1(a)mid.individual.net... > > "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? Electric waves propagate in nonconducting dielectric materials also. > > BONG! BONG! BONG! This is a common mis-perception. An antenna does not > create EM radiation. I "guides it." The transmission line guides it to the end. The end radiate. > > 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. In the sources the electrons start oscillate. > > 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. Once the electrons reaches the antenna end, the voltage is doubled and the end radiate (alternate electric field). > > 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. It is like the Stokes drift: http://en.wikipedia.org/wiki/Stokes_drift The electrons are expeled (field emission) and absorbed but the netto effect is not zero. >They are unbroken from the source to as far out as you care to plot them. S*
From: Bill Miller on 24 Feb 2010 13:39 "Benj" <bjacoby(a)iwaynet.net> wrote in message news:2bb0aba3-6837-48aa-bf34-83fee8cbf5a7(a)a18g2000yqc.googlegroups.com... On Feb 23, 6:09 pm, "Bill Miller" <billmillerkt...(a)worldnet.att.net> wrote: > BONG! BONG! BONG! This is a common mis-perception. An antenna does not > create EM radiation. I "guides it." <snip> I know what your are saying but I'm not sure I "buy" it. It's certain that power in a DC sense changes to RF in a tube or klystron etc. and it's also certain that the resulting currents of that tube also create RF fields that are guided from it to an antenna and into space. But my point would be that from the tube to an antenna the power is in fact a DUAL entity. There are CURRENTS flowing in the transmission line and antenna as well as fields about or within those entities. And time- changing currents are the source for the electric and magnetic fields measured by the Poynting vector. Hence there is something of a quandary there in that one can consider the power in the current or the power in the fields. HOWEVER, beyond the surface of the antenna that changes. Beyond the antenna there are no currents in space. Hence we see two critical "turning" points in our transmitter. One is at the tube where DC power changes to high frequency power and another at the antenna where actual currents are left behind and pure fields are propagated onward! This then leaves a question. Are the fields of the transmission line propagating on the antenna and then launched into space or do the currents from the transmission line create an excitation of a resonant "circuit" which is the conductive antenna structure of which the currents flowing upon that structure are the source (charges and currents are the ONLY sources for EM fields) for the EM fields launched into space. I suggest that in the case of many antennas of the classic kind (dipoles etc) it is the latter. Of course as I intimated above, the other situation can also occur. This is when fields from the transmitter are guided to dielectric antennas where they are then guided into space. These are called "traveling wave antennas". As I said before, it's a popular misconception. To begin, let me suggest you re-read Poynting's original paper on what we now call the Poynting Vector. (Get a version using current scientific characters, rather than his original wherein the formulas look like they had been copied from over the gates to Mordor.) This *may* be the first widely published declaration that conductors do not conduct. They guide. In the process, they detract from energy transmission by absorbing some of the energy. All conductors radiate. Some do it more efficiently than others. Sometimes transmission lines are made deliberately "leaky." Others "morph" from being non-radiating devices to radiating devices. "Horn" microwave antennas and large wire devices like rhombics and "Vee" antennas do a nice job of smoothly transforming energy from "contained" to radiating. Qualitatively, there is no difference between the energy that is present at the output a transmitter, the energy around the transmission line(s) and the energy that is present at an antenna. >The fact that charges and currents are the source of E and >H fields makes things like transmission lines and >antennas where both >fields and currents are present an interesting case. It's >sort of like >arguing which is the more "fundamental" field, A or B. >Since changing >currents are the cause of fields, I argue that current is the >fundamental quantity. >That's my assessment. Yep. Changing currents and accelerating charges cause the E and H. But this is done in the "transmitter." From that point on, including the transmission lines, any matching networks, the antenna and free space, everything is passive. All the best, Bill
From: Cwatters on 25 Feb 2010 05:03
"Benj" <bjacoby(a)iwaynet.net> wrote in message news:4704dd32-fd8f-46cd-a3d0-01b1c81f600d(a)u9g2000yqb.googlegroups.com... 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? but it also depends on the volume not the surface area. |