What is your EM crankosity?
in [Relativity]
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From: Androcles on 24 Sep 2009 17:30 "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message news:7i26beF2vho02U1(a)mid.individual.net... > > "Androcles" <Headmaster(a)Hogwarts.physics_o> wrote in message > news:k2Qum.117169$tM2.101859(a)newsfe23.ams2... >> >> "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message >> news:7i1r50F2v3gcgU1(a)mid.individual.net... >>> >>> "Androcles" <Headmaster(a)Hogwarts.physics_o> wrote in message >>> news:ovMum.150320$Xh5.91831(a)newsfe01.ams2... >>>> >>>> "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message >>>> news:7i1dqvF2vn8paU1(a)mid.individual.net... >>>>> >>> <snip>> >>>> For an RC circuit, >>>> >>>> a-----/\/\/\/\/\/----b-----||------c >>>> >>>> merely allow the voltage across bc to reach the value across ac >>>> (charge the capacitor) and then reverse the polarity across ac >>>> and measure bc before the cap discharges. >>>> It's called voltage doubling and you can block the discharge >>>> of the cap with a diode. >>>> http://en.wikipedia.org/wiki/Voltage_multiplier >>>> >>>> If you disagree then I do not care what your opinion is. >>>> Actually I don't care what your opinion is even if you agree, >>>> it won't prevent voltage multipliers working. >>>> >>> Well... lets add a few MORE components and make the simple RC circuit >>> into an inverter so that you can get whatever value that you wish across >>> the capacitor. >> >> There ya go. Who said it couldn't be done? >> >> <snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip> >> >> Oops, nothing left. >> Do not bother to reply, I shall snip it first. >> <snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip>
From: Androcles on 24 Sep 2009 17:30 "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message news:7i26fcF2vem52U1(a)mid.individual.net... > > "Androcles" <Headmaster(a)Hogwarts.physics_o> wrote in message > news:l2Qum.117170$tM2.110504(a)newsfe23.ams2... >> >> "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message >> news:7i1u2eF2vqaeaU1(a)mid.individual.net... >>> >>> "Androcles" <Headmaster(a)Hogwarts.physics_o> wrote in message >>> news:D7Mum.182214$I07.168057(a)newsfe04.ams2... >>>> >>> <snip> >>>> E and B are 90 degrees out of phase in radio waves! >>>> One causes the other, energy is conserved. >>> <snip> >> >> Gladly. Always pleased to provide a snip when requested. >> There ya go, mission accomplished. >> Anything else I can snip for you? >> >> <snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip><snip>
From: Bill Miller on 24 Sep 2009 18:10 "Don Kelly" <dhky(a)shawcross.ca> wrote in message news:ZxRum.442702$Ta5.326405(a)newsfe15.iad... > > > -- > > "Don Kelly" <dhky(a)shawcross.ca> wrote in message > news:UZCum.12091$tG1.1922(a)newsfe22.iad... >> >> >> -- >> >> "Benj" <bjacoby(a)iwaynet.net> wrote in message >> news:5e4d53b6-63ae-46f3-8396-6f7e58e26a25(a)f10g2000vbf.googlegroups.com... >> On Sep 22, 11:40 pm, "Don Kelly" <d...(a)shawcross.ca> wrote: >> >> >> As to the questions- >> #1 Poynting points the way- I would suggest that there is a double >> frequency power component which has a 0 time average. This is somewhat of >> an intuitive answer. > -- > I now have the problem that the described wave is apparently a TEM wave > for which E and H are 90 degrees out of phase. Since the E and H > components are related by root(muo/epso) which is real, it would appear > that the 90 degree phase shift is a wee problem. thrown into the picture. > I should have spotted this before. > > -- > Don Kelly > dhky(a)shawcross.ca > remove the x to reply Exactly! If you can find a diagram that "illustrates" a TEM wave, you'll note that the two waves are "mechanically" at 90 degrees, but they are in temporal phase. The Field Theory book that I use is by Guru and Hiziroglu and the illustration there is figure 8.3 on page 312. In other words, when the E field is maximum, so is the H field. And *that* indicates that neither one can possibly be "causing" the other. There are much more rigorous ways of proving this, but this should do for starters. All the best, Bill
From: Don Kelly on 24 Sep 2009 18:49 -- "Benj" <bjacoby(a)iwaynet.net> wrote in message news:efa75854-a215-4a6e-abc1-dc3d8eb7134d(a)g6g2000vbr.googlegroups.com... On Sep 24, 12:56 am, "Don Kelly" <d...(a)shawcross.ca> wrote: > As to the questions- > #1 Poynting points the way- I would suggest that there is a double > frequency > power component which has a 0 time average. This is somewhat of an > intuitive > answer. What you say is true. The Poynting vector shows that the wave is transporting energy. However the essence of the question has to do with whether E and B lag each other by 90 degrees (they do not) and whether or not wave propagation is the result of energy ping-ponging back and forth between E an B. (it does not because they are in phase). ------------ I have already sent an additional note recognizing this. ------------------ > #2 False: there is no such thing as an induced current. Faraday's Law > deals > with induced voltage. No, that isn't the idea. Induction is where an electric field is generated in space. That field can produce forces on free charges (as in wires) to create a current. Actually we talk about "emf" which represents potential that is the integral of the field with a test charge over distance. A tricky aspect is that this field is not conservative. Faraday's law deals with all these things. ---- And Faraday's law deals with induced emf's (or voltages) . Certainly the field is not conservative ( this is something discussed several months ago. Recognizing what you say, consider a nearly closed loop of 0 impedance and close it with a resistance in parallel with as close to an ideal voltmeter as possible. Vary the resistance and plot the voltage and current (calculable) against the resistance (yes corrections for meter resistance can be made) and note that as the resistance increases, the voltage remains constant --in other words behaving like an ideal voltage source. It is true that the act of measurement does involve a current but, from a working point of view, Faraday's law fits quite well for any practical purpose and fits observed data. Where the problem comes in, is I said that it is a CHANGING MAGNETIC FIELD that creates this induced E field. This is flat out wrong. Faraday's law may be a true relationship, but it's NOT a causal relationship. The actual true mechanism is that a changing current (charges) creates BOTH a magnetic field AND the induced electric field that can produce the induced current in wires etc. Both the magnetic field AND the electric fields travel away from the changing source current at the speed of light and hence are simultaneous and therefore cannot "cause" one another. --------------- Certainly that is correct- moving charges produce the magnetic field - But, again, the magnetic field can be expressed in terms of the moving charges and, while not causal, is that for practical purposes, for physicists as well as engineers, expressing B as a factor, in some cases, of some unknown charge moving at an unknown velocity (and, at least in one example, involving a v cross E relationship) is rather inconvenient. Again, it is the changing magnetic field that is observable and related to the induced E field. One coud also say that a battery produces an emf because of some (known) chemical reaction but we don't actually deal with the chemistry involved in dealing with the application of a battery unless there is some overriding reason to do so. Ditto with the application of EM theory in the case of the magnetic field. --------------------- Thus, Answer is "false", but not for the reason you say. > #3 False: any emf induced will depend on the rate of change of the flux > enclosed. Given that, Maxwell's appropriate equation is usually written > (in the integral form) with the time derivative term inside the integral > but > can be written with the time derivative outside the integral allowing for > coil area changes - this is the basis for taking the circuit form for > inductances as d(Li)/dt allowing for speed voltage (L changing) as well as > transformer voltage (i changing) in modelling electric machines- and the > speed voltage (often due to changes in the effective area of the coil) is > dominant in most machines. Guess what-it coincides with reality! So you are saying the statement is true? Nope. Wrong. The statement is usually true but not ALWAYS true. You sort of have the idea but not quite. It has to do with HOW you change the amount of flux enclosed within the circuit. If you have a wire loop and just grab it and bend it to a new outline, indeed the changing flux will always relate to an emf created in the circuit. On the other hand if the circuit changes shape with a SWITCHING scheme, you find that great flux changes can occur but there will be ZERO emf induced in the circuit. For an example see Feynman Lectures Vol II Section 17-2 "exceptions to the flux rule". Especially look at the rocking plate apparatus Fig. 17-3. Feynman doesn't really explain how this apparatus "works" but if you think about it carefully you'll see it is a disguised "switching" device. Switching devices do not follow the "flux rule", because a requirement of Maxwell's Equations is that functions be continuous and differentiable. Switching setups are not. ---- and how does one build such an ideal switching machine that has no transition period and no radiation? In other words, Maxwell's Equations as well as their approximation, circuit theory, fail mathematically in such situations (although there are ways around this- all mathematical). The ideal switch also fails- in implementation. I do not have Feynman so I cannot look up your references (and the nearest library that may have them is 200Km away. Do you have a reference on line to such a switched circuit? Anyhow, thanks for the information, I have heard some of it before but it is good to get a refresher and some new tid-bits Don Kelly dhky(a)shawcross.ca remove the x to reply
From: Bill on 24 Sep 2009 21:43
----- Original Message ----- From: "Androcles" <Headmaster(a)Hogwarts.physics_o> Newsgroups: sci.physics,sci.physics.relativity,sci.physics.electromag Sent: Thursday, September 24, 2009 6:21 PM Subject: Re: What is your EM crankosity? > > "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message > news:7i28trF2vnc2vU1(a)mid.individual.net... > > >> If you can find a diagram that "illustrates" a TEM wave, you'll note that >> the two waves are "mechanically" at 90 degrees, but they are in temporal >> phase. > > Really? > http://www.androcles01.pwp.blueyonder.co.uk/AC/Photon.gif > > If both E and M are zero at the same instant, energy is not conserved. > I have two comments. Since Androcles will immediately <snip> this, I am addressing this -- instead -- to any that are interested in understanding more about EM. 1. In my previous post, I referenced a diagram in a respected textbook recommended to me by a UK EM Professor and friend. Androcles replied with a diagram of unknown antecedents that came from his own website. I wonder which of the two might have higher credibility? 2. Androcles is missing the point when he says (from above) that, "If both E and M are zero at the same instant, energy is not conserved." The point that Androcles is missing is that, at the time that E and M are zero, *there is no energy to conserve.* "E and M are zero" means that at that specific time, and location, *no energy whatsoever is present.* This lack of understanding is, I suspect, based on one of a physics student's first encounters with oscillation. This is the classic spring with a weight. In this embodiment, we pull the weight down, thus storing potential energy in the spring. We let go, and the weight rebounds gaining kinetic energy until gravity pulls it down. This swapping of kinetic for potential energy is essential for the weight to bounce up and down. From this we learn about *one* way to generate a sine wave. The EM case is different. Although we usually look at an EM wave as a pair of sinusoidal waveforms (like what we get with the idealized spring) it is important to understand that an EM field is *not* oscillatory. Both the E and the H fields are independent, and are caused by and at the same source, at the same time. OK...If the Spring's sinusoidal waveform comes about because of initial conditions and a swapping of energy between potential and kinetic energy sources, where does the energy come from to establish an EM wave's sinusoidal nature and propel the EM wave outward? It comes from a "transmitter" that continuously feeds new energy into the "antenna" so that an EM wave is emitted into space. This is not very complicated. All that is required is to think about the difference between a wave whose existence depends on the "swapping" of energy to sustain it, and a wave whose existence depends on an external power source of some sort. Here, Androcles, let me save you the effort: <snip> <snip> <snip> <snip> <snip> <snip> <snip> <snip> All the best, Bill |