What is your EM crankosity?
in [Relativity]
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From: Androcles on 23 Sep 2009 21:17 "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message news:7hvhimF2tnfrjU1(a)mid.individual.net... > > "Androcles" <Headmaster(a)Hogwarts.physics_o> wrote in message > news:T_uum.184169$_Q3.136829(a)newsfe20.ams2... >> >> "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message >> news:7hvbgtF2vr29rU1(a)mid.individual.net... >>> > <snip> >>> One interesting side note is that we are all taught that a >>> capacitor/resistor network *always* charges and discharges in an >>> exponential fashion. As such, there are two absolutely true statements >>> (we are taught.) >>> >>> First, the voltage across a capacitor in an RC network can *never* >>> exceed the supply voltage. >>> >>> Second, the voltage can *never* go to ZERO nor to 100% of the supply >>> voltage. >>> >>> Both of the above can be shown to be false for specific capacitor >>> configurations. And they are easy (and kinda fun) to model in SPICE. >>> >>> Bill >> >> Nobody ever taught me the voltage across a capacitor in an >> RC network can *never* exceed the supply voltage. I expect you are >> thinking DC in which case it would be true, but clearly if one applies >> AC the voltage across a capacitor approaches the peak-to-peak voltage. >> > > Well, if the supply voltage is AC OR DC, we are taught No no, Bill... YOU are taught. *You* are not "we". *I* am not "we". *I* have a different teacher. > that the voltage across the capacitor cannot exceed the supply voltage. > What you may be thinking about is an RC circuit in a rectifier > arrangement. In that case, The voltage across the capacitor can approach > the peak value of the incoming signal. That value is higher, of course, > than the RMS value. > > Otherwise, my comment stands. You can say you what you were taught all you want to, Bill, and I will offer no argument. Just don't say "we". I did not attend any dumb American schools, *I* was educated in England. "We" were not. Nobody ever taught me the voltage across a capacitor in an RC network can *never* exceed the supply voltage, even if some American idiot taught you that.
From: Androcles on 23 Sep 2009 21:26 "Bill Miller" <billmillerkt4ye(a)worldnet.att.net> wrote in message news:7hvhucF2vl87lU1(a)mid.individual.net... > > "Benj" <bjacoby(a)iwaynet.net> wrote in message > news:304e3b17-a155-40e2-9687-9db1202a029a(a)z34g2000vbl.googlegroups.com... > On Sep 23, 2:53 pm, "Bill Miller" <billmillerkt...(a)worldnet.att.net> > wrote: >> "Benj" <bjac...(a)iwaynet.net> wrote in message > > ======================= > > DING! DING! DING! DING! DING! > > Folks we have a WINNER! > (and it wasn't the Jewish heritage of Uncle Al, the jargon glossary). > (It also wasn't ANY of the ad hominems who spend their days calling > everyone else stooopid who were scared to enter) > > ======================= > > ALL statements are demonstrably false! > > Score: = number of statements you said were false > > 10.You are a major kook and are the crankiest. You know nothing about > science and should go read a freshman physics text book. Don�t forget > your tinfoil �reading helmet� when doing that. You�ll be lucky to stay > alive. > > 9. You are very much out of the mainstream and know nothing about > science. You�re fired. And you�ll never work or publish in science > again. > > 8. You have major problems in your profession. You just got a memo > from the boss to come to his office to see if you can be �brought > round� before it�s too late. > > 7. Your paper has been rejected for publication even though none of > the topics covered here were mentioned in it. > > 6. You have serious gaps in your electromagnetic understanding. To > keep your job you�d better tell everyone your specialty is acoustics. > > 5. You have a pretty good understanding of science but half your > answers are wrong. But that�s OK since you probably teach high > school. > > 4. Your traditional science is pretty good, but you made a handful of > �mistakes�. You are probably an engineer. > > 3. Since you only made three �mistakes�, you probably are a college > physics professor whose primary responsibility is teaching freshman > physics. > > 2. Making just two deviations from traditional understanding likely > means you are a college physics professor, but your primary > responsibility is to teach, �physics appreciation� to education > majors. > > 1. You are a post-doc employed on a government funded research > project on which you are doing all the work and thinking and for which > the full professor whose name and reputation are on the original > proposal will take all the credit. > > 0. You are a highly paid government project administrator with a > perfect understanding of traditional science. You have a Ph. D., you > have hundreds of patents with your name on them and thousands of > papers that list you as one of the authors. You are an ultimate > authority ready to debunk any crank science when asked to do so by the > major media. > ****************** > > Um... > > I hate to ask, but... > > Well... > > That is... > > Are there any openings at the Burger King where you work? > > Bill I understand the janitor was fired for mopping the toilet bowl with a burger bun and then ate the evidence with fries, ketchup and a healthy dose of salt. It wasn't his lunch break so he had to be dismissed.
From: Benj on 24 Sep 2009 00:30 On Sep 23, 7:29 pm, "Mary" <inva...(a)invalid.com> wrote: > you failed to state your intent in OP Hey, "Mary" it's obvious that the intend of any post is to stimulate discussion on the topic. > You know very little about EM or physics. Care to elaborate why you feel that way? Proof of how any or all of the statements are true would be a good start on showing us what you know. Otherwise it's just one more anonymous opinion worth what we paid to get it.
From: Inertial on 24 Sep 2009 00:42 "Benj" <bjacoby(a)iwaynet.net> wrote in message news:58ef53b4-fb4e-4c90-87c9-71acbe7ba2d4(a)r36g2000vbn.googlegroups.com... > On Sep 23, 7:29 pm, "Mary" <inva...(a)invalid.com> wrote: > >> you failed to state your intent in OP > > Hey, "Mary" it's obvious that the intend of any post is to stimulate > discussion on the topic. > >> You know very little about EM or physics. > > Care to elaborate why you feel that way? Proof of how any or all of > the statements are true would be a good start on showing us what you > know. Otherwise it's just one more anonymous opinion worth what we > paid to get it. > Personally, I don't see the problem with posing some questions to test readers understanding of EM theory.
From: Benj on 24 Sep 2009 02:19
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). > #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. 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. 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. Cheers. |