|
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
It just shows that Hecht was right when he said standing waves probably don't deserve to be called waves. Maybe you should try to understand why Hecht would say such a thing. I think he might have said it because he's not particularly good with words. If anything, he probably should have said that standing waves should just be called interference patterns. From Websters: wave - a shape or outline having successive curves; an undulating line or streak or a pattern created by such lines; something that swells and dies away There is no need to sketch or calculate anything. A diagram showing the relationship of the E-field vector and the H-field vector is in every E&M and optics book I have ever seen. Yes, and that diagram is for a *TRAVELING WAVE*, not for a standing wave. Please find a reference with the E-fields and H-fields diagrammed for a standing wave and get back to us. Better yet, consider there is a need to sketch the fields if for no other reason, just to prove me wrong. I could be wrong, but don't E-fields and H-fields from traveling waves superpose to form net E-fields and H-fields? Wouldn't the net fields have vectors whose direction and magnitude are determined by the vectors which correspond to the traveling wave fields? Wouldn't the net field generated by a radiator having these waves traveling on it look like a standing wave? Is there any reason to consider standing waves on an antenna other than as a simple way to analyze its radiation pattern? ac6xg |
Standing morphing to travelling waves, and other stupid notions
Jim Kelley wrote:
I think he might have said it because he's not particularly good with words. If anything, he probably should have said that standing waves should just be called interference patterns. I'll buy that, Jim. I believe that Hecht left out the adjective, "EM". If he meant standing waves don't deserve to be called EM waves, I agree 100%. However, standing waves seem to meet the broad definition of "wave". I could be wrong, but don't E-fields and H-fields from traveling waves superpose to form net E-fields and H-fields? Wouldn't the net fields have vectors whose direction and magnitude are determined by the vectors which correspond to the traveling wave fields? Of course. Now try to convince Gene of that fact of physics. In spite of his earlier assertions about the differences between traveling waves and standing waves that agreed with my side of the argument, he seems to have switched sides. (For political reasons)? -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
Jim Kelley wrote: I think he might have said it because he's not particularly good with words. If anything, he probably should have said that standing waves should just be called interference patterns. I'll buy that, Jim. I believe that Hecht left out the adjective, "EM". If he meant standing waves don't deserve to be called EM waves, I agree 100%. However, standing waves seem to meet the broad definition of "wave". I could be wrong, but don't E-fields and H-fields from traveling waves superpose to form net E-fields and H-fields? Wouldn't the net fields have vectors whose direction and magnitude are determined by the vectors which correspond to the traveling wave fields? Of course. Now try to convince Gene of that fact of physics. In spite of his earlier assertions about the differences between traveling waves and standing waves that agreed with my side of the argument, he seems to have switched sides. (For political reasons)? Cecil, I have no idea why you would introduce "political reasons" into this, but no matter. My head hurts from pounding it into the brick wall, so I will give up. It would be really amusing to see you scramble to rotate the vector axis of the magnetic field (or the E-field) as it reflects from an interface. Since the E-field and H-field are related by curl relationships as shown in the Maxwell equations, it would be interesting to see how one could have related E-fields and H-fields at "0 degrees" and "180 degrees" as you claim. As a self-proclaimed math expert I am sure you understand the properties of the curl operator. This is very basic stuff, and it is in the standard textbooks, probably even in Hecht. 73, Gene W4SZ |
Standing morphing to travelling waves, and other stupid notions
On Jan 15, 6:54*pm, Cecil Moore wrote:
Keith Dysart wrote: It would be valuable if you could indicate which of the possible definitions of "*NET* energy moving" you mean. Net energy is the difference between the average forward energy and the average reflected energy. Okay. Option 2. This is the same as subtracting the indications that a Bird wattmeter would provide for the forward and reflected power. I like this definition for NET energy transfer. Please forget instantaneous values. Instantaneous voltage and current are obviously valuable concepts. Now the next question. When the instantaneous power is always 0, is any energy transferred? ...Keith |
Standing morphing to travelling waves, and other stupid notions
Gene Fuller wrote:
It would be really amusing to see you scramble to rotate the vector axis of the magnetic field (or the E-field) as it reflects from an interface. Since the E-field and H-field are related by curl relationships as shown in the Maxwell equations, it would be interesting to see how one could have related E-fields and H-fields at "0 degrees" and "180 degrees" as you claim. As a self-proclaimed math expert I am sure you understand the properties of the curl operator. This is very basic stuff, and it is in the standard textbooks, probably even in Hecht. It certainly applies to EM waves but what you are missing is that it doesn't apply to standing waves which are NOT EM waves. Tomorrow I will list the Ramo & Whinnery characteristics of an EM wave. Standing waves don't meet those characteristics. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Keith Dysart wrote:
Now the next question. When the instantaneous power is always 0, is any energy transferred? Now for the real question. When the net instantaneous power is 0 at a point with non zero power on each side of that point, is any energy transferred? The answer is - of course - equal amounts in either direction. The sum of the two Poynting vectors is zero. Until you can provide a reference or example of a reflection occurring in a homogeneous medium, you have proven nothing except that you can fantasize. Ramo & Whinnery imply that reflections are impossible unless the reflection coefficient changes magnitude which it doesn't with a constant Z0. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
On Tue, 15 Jan 2008 14:18:15 -0800
Roy Lewallen wrote: Roger Sparks wrote: I can see why you find "no power" at the zero voltage point, but does that imply that there is no energy flow and no power from every perspective? As I write, I am struggling how to clearly differentiate between "power" as "work done" and energy as "capacity to do work", and what "network" are we defining. Power at a particular point on the line is the rate of energy flow past that point. It does no imply that any work is done anywhere, since any energy flowing past the point can be stored. That is, in fact, exactly what happens with the open circuited line in my analyses and illustrated with TLVis1. You can see from the TLVis1 demo 4 that power is present at all times and places along the line except a few select points. No work is being done; energy is simply moving back and forth along the line and between the E and H fields. Are you objecting to my link between power and work? I can understand how we might think of a moving voltage wave (on a transmision line) somewhat like a battery that moves along a straight line. With that view, there would be no power acting on the line, no work, and there would be no evidence of current. If a capacitor discharges, work is done on the circuit receiving the discharge. It takes work to charge a capacitor. Are you thinking that on a continuous capacitor like a transmission line the energy just "slides" along (like a train on tracks) without change of energy, like a battery moving along? In my view, logic demands a smooth flow of power and energy from source to load. We should be able to account for both energy and power for every instant of time, over every inch of distance. I thought you were doing that in TLVis1 demo 4. . . . I personally define power as a state/condition where "work 'is being' done", . Power must act over time and have a physical movement component. Voltage by itself does not fulfill this definition because no movement is observed. Current is movement, voltage is only an indication of where a concentration of charges is found. Of course you're free to define anything in any way you choose. But you've chosen a definition that's different from the one accepted in all of electrical circuit analysis and all textbooks. So you can expect to have a good deal of difficulty communicating with people who are acquainted with the universally understood definition and assume that's what you mean, rather than your own personal definition. To them, power is the time rate of energy flow, dE/dt, period. Are you again objecting to my link between power and work? This definition sounds consistant with power flowing on the transmission line. We seem to fulfill the power definition of energy flow on a transmission line but you make the statement "No work is being done". Would you object to my example of requiring work to charge a capacitor? . . . Roy Lewallen, W7EL 73, Roger, W7WKB |
Standing morphing to travelling waves, and other stupid notions
Roger Sparks wrote:
On Tue, 15 Jan 2008 14:18:15 -0800 Roy Lewallen wrote: Roger Sparks wrote: I can see why you find "no power" at the zero voltage point, but does that imply that there is no energy flow and no power from every perspective? As I write, I am struggling how to clearly differentiate between "power" as "work done" and energy as "capacity to do work", and what "network" are we defining. Power at a particular point on the line is the rate of energy flow past that point. It does no imply that any work is done anywhere, since any energy flowing past the point can be stored. That is, in fact, exactly what happens with the open circuited line in my analyses and illustrated with TLVis1. You can see from the TLVis1 demo 4 that power is present at all times and places along the line except a few select points. No work is being done; energy is simply moving back and forth along the line and between the E and H fields. Are you objecting to my link between power and work? I have to correct my statement. The strict definition of work is the same as energy. So moving energy is technically doing work, even if no energy is being dissipated or being put to any useful purpose. What I meant but failed to say accurately is that no net work is being done. All energy being moved is being moved back. None is being converted to heat (dissipated), mechanical energy, or other useful work. Consider a resonant circuit or, for that matter, an open or short circuited transmission line. Energy is moved back and forth each cycle, resulting in non-zero power, but without any *net* work being done. It's possible that by "power" you mean "average power", which is not the same as (instantaneous) power. (This is exactly the mistake I made, using "work" to mean "net work".) The average power (and net work done) is non-zero whenever the amount of energy moved in one direction during one half the cycle isn't equal to the amount moved the other way during the other half of the cycle. I can understand how we might think of a moving voltage wave (on a transmision line) somewhat like a battery that moves along a straight line. With that view, there would be no power acting on the line, no work, and there would be no evidence of current. Sorry, that doesn't make sense to me. A traveling voltage wave on a transmission line is always accompanied by a current wave, and the ratio of voltage to current is equal to the line's Z0 at every point and every time. If a capacitor discharges, work is done on the circuit receiving the discharge. That's true. No net work is necessarily done -- if it's discharged into an inductor, the energy is simply stored in the inductor, and returned later by the inductor doing an equal amount of work on the capacitor. It takes work to charge a capacitor. Yes, in the strict instantaneous sense. Are you thinking that on a continuous capacitor like a transmission line the energy just "slides" along (like a train on tracks) without change of energy, like a battery moving along? A transmission line has both distributed capacitance and inductance. Energy moves between the two. The little program TLVis1 I created and posted a link to shows this graphically in demo 4, with the energy stored in the capacitance being in one color and the energy stored in the inductance another color. You can clearly see how the energy moves back and forth between the two each cycle. In my view, logic demands a smooth flow of power and energy from source to load. Your logic is flawed. A load which contains both resistance and reactance has energy flow in one direction during half the cycle and energy flowing the other direction during the other half. Because of the resistance, the two aren't equal; the difference is the energy being dissipated each cycle. If the load is an open or short circuit, no energy flows to the load at all. If the load is purely reactive, it stores the energy for half the cycle and returns it during the other half. We should be able to account for both energy and power for every instant of time, over every inch of distance. I thought you were doing that in TLVis1 demo 4. I am indeed. It shows exactly that. If you'll look carefully at the graphs, you'll see that it demonstrates what I've said above. . . . I personally define power as a state/condition where "work 'is being' done", . Power must act over time and have a physical movement component. Voltage by itself does not fulfill this definition because no movement is observed. Current is movement, voltage is only an indication of where a concentration of charges is found. Of course you're free to define anything in any way you choose. But you've chosen a definition that's different from the one accepted in all of electrical circuit analysis and all textbooks. So you can expect to have a good deal of difficulty communicating with people who are acquainted with the universally understood definition and assume that's what you mean, rather than your own personal definition. To them, power is the time rate of energy flow, dE/dt, period. Are you again objecting to my link between power and work? I apologize for my careless use of "work". Instantaneous power is the rate of flow of energy, or work. Average power is the average rate of flow of energy or work. If the average power is non-zero, net work is being done, e.g., energy is being dissipated in a resistance or being radiated. But instantaneous power can be non-zero without this occurring. This definition sounds consistant with power flowing on the transmission line. Which definition, yours or the one used by everyone else involved with electrical circuits? I maintain that power doesn't "flow". Energy flows, and power is the rate of that flow. The standard definition says nothing about power "flowing", on a transmission line or anywhere else. We seem to fulfill the power definition of energy flow on a transmission line but you make the statement "No work is being done". Please correct that to be "no *net* work is being done. It was made to refer to the open-circuited line in my example. The average power everywhere is zero, as you can see from demo 4 - the power waveform oscillates equal amounts on both sides of zero. No net energy is being transferred or dissipated. Would you object to my example of requiring work to charge a capacitor? I stand corrected - work is required. But the work can be returned. Roy Lewallen, W7EL |
Standing morphing to travelling waves, and other stupid notions
On Jan 16, 12:59*am, Cecil Moore wrote:
Keith Dysart wrote: Now the next question. When the instantaneous power is always 0, is any energy transferred? Now for the real question. When the net instantaneous power is 0 at a point with non zero power on each side of that point, is any energy transferred? The answer is - of course - equal amounts in either direction. So you seem to be claiming that the following two statements can be simultaneously true: 1. Power [recall p(t)=v(t)*i(t)] is the rate at which energy is transferred. 2. Energy can be transferred when the power is zero. To my simple intellect, one of these statements must be false. ...Keith |
Standing morphing to travelling waves, and other stupid notions
Roy Lewallen wrote:
Which definition, yours or the one used by everyone else involved with electrical circuits? I maintain that power doesn't "flow". Energy flows, and power is the rate of that flow. The standard definition says nothing about power "flowing", on a transmission line or anywhere else. I agree with you. If energy is measured in joules and energy flow is measured in joules/sec, then it seems to me that if power is measured in watts, then "power flow" would have the dimensions of watts/sec or joules/sec^2, which doesn't make any technical sense. The units of the power-flow vector are watts/unit-area. That's a value fixed in space-time and that value is not moving. However, most of my college textbooks from the 50s refer to "power flow" as do some folks on this newsgroup. For instance, Ramo & Whinnery talk about an "electromagnetic theorem concerning *flow of power*". A transmission line has both distributed capacitance and inductance. Energy moves between the two. The little program TLVis1 I created and posted a link to shows this graphically in demo 4, with the energy stored in the capacitance being in one color and the energy stored in the inductance another color. You can clearly see how the energy moves back and forth between the two each cycle. Now it is my turn to wax technically correct. If the energy in a standing wave is indeed flowing back and forth between an inductance and a capacitance, then a standing wave is *NOT* an EM wave just as the EM energy flowing in a tank circuit doesn't meet the definition of a wave. Ramo & Whinnery list the properties of a uniform plane wave: [begin quote] 1. Velocity of propagation, v = 1/SQRT(permeability*permittivity). 2. No electric or magnetic field in direction of propagation. 3. Electric field normal to magnetic field. 4. Value of electric field is the intrinsic impedance (ii) times the magnetic field at each instant. 5. Direction of propagation given by direction of ExH. 6. Energy stored in electric field per unit volume at any instant and any point is equal to energy stored in magnetic field per unit volume at that instant and that point. 7. Instantaneous value of Poynting vector given by E^2/ii = ii*H^2, where E and H are the instantaneous values of total electric and magnetic field strengths. [end quote] A standing wave doesn't satisfy any of those properties. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Keith Dysart wrote:
1. Power [recall p(t)=v(t)*i(t)] is the rate at which energy is transferred. Since we are dealing with superposed waves that would be the rate at which net energy is transferred. 2. Energy can be transferred when the power is zero. To my simple intellect, one of these statements must be false. Using the rules for superposition, treat each wave separately and superpose them for a net result. And it certainly depends upon what definition of "transfer" that you are using. I am using, from Webster's: "transfer - move" Would you please post your definition of "transfer". The forward wave is moving energy across the zero power point. The reflected wave is moving an equal magnitude of energy in the other direction across the zero power point. The Poynting vectors for the forward wave and reflected wave are equal in magnitude and opposite in direction. There is of course zero net power transfer and points where the net instantaneous power equals zero. I'm going to keep reminding you that, until you provide a reference or example of reflections occurring within a homogeneous medium, nothing that you have to say about the subject is linked to reality. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
On Jan 15, 2:27*pm, Roger Sparks wrote:
On Tue, 15 Jan 2008 06:44:05 -0800 (PST) Keith Dysart wrote: [snip] Well I start with P = V * I, so whenever the current or the voltage is zero, there is no power. Specifically, V and I are measured at the terminals of a network and P will be the power flowing into or out of the network. I can see why you find "no power" at the zero voltage point, but does that imply that there is no energy flow and no power from every perspective? *As I write, I am struggling how to clearly differentiate between "power" as "work done" and energy as "capacity to do work", and what "network" are we defining. Let's begin with the network. *Drawing from your words below, we have two networks, one to the left and one to the right of our zero voltage point. *When we test voltages on either side of the zero point, we find voltage. *The question now is: "Which network did we join when we measured voltage?". *The answer is: "We joined the network that we measured.". *When we measure exactly in the center between networks, we join neither network. * That is the best way. And that way we can measure the flow between the networks. For another way of looking at the two networks, *let us place our voltage probes on each side of the zero voltage point on a/the wire connecting the two networks. *We will detect a voltage and a current for any of the standing wave systems we are discussing. *By changing our points of reference, we find that power is applied to the zero voltage zone during the instant of time the measurement is made. But if we move the probes, we have changed the amount of 'network' on either side. I personally define power as a state/condition where "work 'is being' done", . *Power must act over time and have a physical movement component. *Voltage by itself does not fulfill this definition because no movement is observed. *Current is movement, voltage is only an indication of where a concentration of charges is found. I am not convinced about 'physical'. Consider heat, light. In the case under discussion, there are two networks, one to the left of the point on the line and one to the right and we are measuring the power flowing between these two networks. For an example of current without power, consider a loop of superconductor with a current flowing in it. No voltage, no power, but there is current. I agree. *We could place voltage probes between any two points on the superconducting loop and not find voltage. *Power is not being applied nor extracted from the superconducting loop system. *I think we would all agree that energy is stored in the superconducting loop with current flowing. Current is defined as movement of charges, and charges have energy by definition (how can they be charges without energy?). Consider an object flying through space. No work is being done (and therefore there is no power), but the object still has kinetic energy. Another point, the current is observed to change directions during the cycles, polarity also changes on each side of the zero voltage point. *Where might the polarized energy come from if it does not cross the zero voltage point? A thought experiment I have found useful is to consider a simple resonant circuit made of an ideal capacitor and inductor. Charge the capacitor to 10 volts and then connect the inductor. A sinusoidal voltage and current will appear in the circuit. Just as the inductor is connected: - all the energy is stored in the capacitor - the voltage on the capacitor is maximum - there is no current in the inductor After connecting the inductor: - energy starts to transfer to the inductor - the voltage on the capacitor is dropping - the current in the inductor is increasing Some time later: - the voltage on the capacitor is 0 - the current in the inductor is maximum - there is no energy stored in the capacitor - all the energy is stored in the inductor - no energy is moving from the capacitor to * the inductor But the inductor insists that current continue to flow: - the capacitor begins to charge with a negarive * voltage - energy begins to transfer from the inductor * back to the capacitor (note the change in the * direction of energy flow) - the voltage on the capacitor is increasing * negatively - the current in the inductor is dropping Sometime later: - the current in the inductor has dropped to * zero - the capacitor has a maximum negative voltage - all the energy is in the capacitor And this continues forever at the resonant frequency of the capacitor and inductor circuit. But no energy is moving from the capacitor to the inductor when the voltage on the capacitor is zero and the current in the inductor is maximum. It is at these times that the direction of energy flow is changing, as well as when the voltage in the capacitor is maximum and the current is zero. When the voltage on the capacitor is zero, the voltage on the entire system is zero, no matter our reference point. *The system energy is completely contained in the moving current with a direction of energy flow completely defined. For an instant, the inductor is like a superconducting loop. From a traveling wave standpoint, the resonant capacitor/inductor system contains a positive wave and a negative wave, equally balanced energy wise. *When the capacitor is completely charged, the positive and negative waves are at the reversal/mid point of the cycle where each wave is maximally displaced from center (which is at the electrical center of the inductor). *When the capacitor is completely discharged, the two waves superimpose and both reside in the inductor at identical times. *The energy of both waves is completely contained in the electromagnetic field that exists outside the wires containing the two traveling waves. *Do the waves exist on the wire at this instant, or have they completely desolved into a space field we observe as magnetic force? *The current seems to be flowing so I would say the waves both continue to exist. When using lumped elements, I do not think I would try to write a description in terms of waves. I can kinda see how like charges could repell so that waves of like polarity might "bounce" but I can't see how waves of opposite polarity might "bounce". *If waves of opposite polarity "bounced", why would the polarity change during the cycle on each side of the "bounce" point? An excellent counter-example. I may have fallen into the trap of looking at the examples that support the argument rather than looking for the ones that don't. This will take some cogitating. Maybe its the end of the line for the "bounce hypothesis". To me, it is much more rewarding to work with traveling waves that pass through one another, *interacting to create standing waves. I don't object to this view, as long as the waves are viewed as having voltages or currents but no power. Have you considered how energy is transfered between elements of the transmission line over time if we do not have an ongoing application of power? *Doesn't one section of line apply power to the next successive section of line an instant of time later after it received applied power? We agree that a transmitter applies power at the input of a transmission line. *Isn't the first section of transmission line just the power source for the second piece of line? Yes. And that is especially visible when the line is excited with a pulse. I think of the traveling waves as transporting power and energy through time and physical distance. *The highest voltage points physically "move" (found in a new location) as time passes, as do the highest current points, and always together in phase. * The difficulty is that some waves definitely transport energy while others do not and I do not see a good explanation for what turns the former into the latter, as happens, for example, when the pulses collide. Some waves transport energy, and some do not! *That distinction bothers me less now that I have participated in this thread for a while. *For me, the traveling wave always has current and voltage in phase, and always carries power. *If I can not find power, then we must have a standing wave. *For me, traveling waves is all that we really have, they are primary. *All other waves flow/result from the traveling waves. * But then do the two travelling waves that make up the standing wave transport energy? When no energy crosses the voltage or current zeroes? And when there are multiple reflections, there are multiple travelling waves in each direction. Do each of these multiple travelling waves independantly transport energy? And even a standing wave has energy moving. Just not past the voltage and current zeroes. [snip] ...Keith |
Standing morphing to travelling waves, and other stupid notions
Keith Dysart wrote:
But then do the two travelling waves that make up the standing wave transport energy? Does a light wave from Alpha Centauri that never encounters anything except free space transport energy? It certainly depends upon your definition of "transport". It has an E-field, a B-field, and a Poynting vector but is it "transporting" energy if it never encounters a load to which to transfer energy? -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
On Tue, 15 Jan 2008 23:35:16 -0800 Roy Lewallen wrote: Roger Sparks wrote: On Tue, 15 Jan 2008 14:18:15 -0800 Roy Lewallen wrote: clip........... In my view, logic demands a smooth flow of power and energy from source to load. Your logic is flawed. A load which contains both resistance and reactance has energy flow in one direction during half the cycle and energy flowing the other direction during the other half. Because of the resistance, the two aren't equal; the difference is the energy being dissipated each cycle. If the load is an open or short circuit, no energy flows to the load at all. If the load is purely reactive, it stores the energy for half the cycle and returns it during the other half. My logic is sound, but perhaps my statement was too brief to convey my meaning. By smooth flow of power and energy from source to load, I do not mean a DC like flow. Instead, I mean that we should be able to trace the time slice that contains the peak energy level of any wave. The energy in this time slice MUST follow the rules of conservation of energy so it will not disappear. The flow of power and energy that I was speaking of is the physical movement of this slice of energy followed through time. Your mention of energy flowing "in one direction during half the cycle and energy flowing the other direction during the other half" would be in reference to a reflection from any source. My contention is that the reflected energy comes first from a source and is traceable to that source. In the case of lumped reactance, we can still trace the peak through time while recognizing that the physical location may not move during the time the peak is within the reactive component. A reactive element can easily return the stored energy any time after the peak has passed, not waiting until the second half of the cycle. Therefore, your emphasis on "If the load is purely reactive, it stores the energy for half the cycle and returns it during the other half." is misleading. I think you want to more simply say something to the effect of "If the load is purely reactive, it stores the energy for some period of time before returning the energy". We should be able to account for both energy and power for every instant of time, over every inch of distance. I thought you were doing that in TLVis1 demo 4. I am indeed. It shows exactly that. If you'll look carefully at the graphs, you'll see that it demonstrates what I've said above. clip..... 73, Roger, W7WKB |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
Now it is my turn to wax technically correct. If the energy in a standing wave is indeed flowing back and forth between an inductance and a capacitance, then a standing wave is *NOT* an EM wave just as the EM energy flowing in a tank circuit doesn't meet the definition of a wave. Ramo & Whinnery list the properties of a uniform plane wave: [begin quote] 1. Velocity of propagation, v = 1/SQRT(permeability*permittivity). 2. No electric or magnetic field in direction of propagation. 3. Electric field normal to magnetic field. 4. Value of electric field is the intrinsic impedance (ii) times the magnetic field at each instant. 5. Direction of propagation given by direction of ExH. 6. Energy stored in electric field per unit volume at any instant and any point is equal to energy stored in magnetic field per unit volume at that instant and that point. 7. Instantaneous value of Poynting vector given by E^2/ii = ii*H^2, where E and H are the instantaneous values of total electric and magnetic field strengths. [end quote] A standing wave doesn't satisfy any of those properties. Cecil, There is at least partial progress. You have quietly dropped the embarrassing confusion between phasors and field vectors. Unfortunately, you are still suffering from a problem in understanding ordinary English language. "Properties" is not the same as "requirements". The "requirements" are simply that Maxwell's equations are obeyed. By the way, a standing wave meets at least 5 of those 7 properties. 73, Gene W4SZ |
Energy and Work
On Tue, 15 Jan 2008 23:35:16 -0800, Roy Lewallen
wrote in the standing wave thread: snip The strict definition of work is the same as energy. So moving energy is technically doing work, even if no energy is being dissipated or being put to any useful purpose. snip How is the word "moving" being used in this quote? Is it used as a gerund meaning "causing to move" or as a participle describing energy that is in motion? I can accept that causing energy to move, as in accelerating charges to launch an EM wave, requires work be done. And that the existence of moving energy in an EM wave implies work was done at some previous time. But the mere movement of energy (say, in free space) does not seem to involve work. If it does, is that work in addition to the work done to launch the energy? Is the amount of work done per unit time (or distance) constant? It cannot be the work done by the moving-while-alternating E-field on all the charges in the universe, since it is claimed that no energy is being "dissipated." Is some transformation of EM energy taking place? TIA for any elucidation. 73, Chuck NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Standing morphing to travelling waves, and other stupid notions
On Wed, 16 Jan 2008 07:00:15 -0800 (PST)
Keith Dysart wrote: On Jan 15, 2:27*pm, Roger Sparks wrote: On Tue, 15 Jan 2008 06:44:05 -0800 (PST) Keith Dysart wrote: [snip] The difficulty is that some waves definitely transport energy while others do not and I do not see a good explanation for what turns the former into the latter, as happens, for example, when the pulses collide. Some waves transport energy, and some do not! *That distinction bothers me less now that I have participated in this thread for a while. *For me, the traveling wave always has current and voltage in phase, and always carries power. *If I can not find power, then we must have a standing wave. *For me, traveling waves is all that we really have, they are primary. *All other waves flow/result from the traveling waves. * But then do the two travelling waves that make up the standing wave transport energy? When no energy crosses the voltage or current zeroes? I can see that my question of how polarity changes on either side of a zero voltage point, and my example of a measurement accross the zero voltage point, did not shake your assumption that no energy crosses the zero voltage point. Having the assumption that energy does not pass the zero voltage point strikes at the heart of the traveling wave concept. I can not see what would reflect the waves to prevent energy passage at the zero voltage point, nor can I see a way to get the results we see between reflection points, if we disallow energy passage at zero voltage points. And when there are multiple reflections, there are multiple travelling waves in each direction. Do each of these multiple travelling waves independantly transport energy? Yes. They merge if they are of one frequency, so tracing of multiple traveling waves is reduced to just the last forward and reflected wave. If the waves are of different frequency, they would each be traced by frequency. And even a standing wave has energy moving. Just not past the voltage and current zeroes. Again, I would consider the traveling wave concept defeated if energy is not allowed to pass the zero voltage point. I think that the change of polarity on each side of the zero voltage point is a convincing argument that energy does pass. A change in measurement point to measure across the voltage point is also convincing to me, that energy must pass. I would hope that those arguments convince you as well. [snip] ...Keith 73, Roger, W7WKB |
Energy and Work
On Wed, 16 Jan 2008 12:26:20 -0500, Chuck
wrote: How is the word "moving" being used in this quote? Is it used as a gerund meaning "causing to move" or as a participle describing energy that is in motion? Hi Chuck, Your question is as about as free of the ongoing myopic failures as any to come down the pike. To put it in the terms of Feynman: "If the force, for instance, is in one direction and the object on which the force is working is displaced in a certain direction, then ONLY THE COMPONENT OF FORCE IN THE DIRECTION OF THE DISPLACEMENT does any work. [emphasis in the original] .... "The rule is 'force times distance,' but we really mean only the component of force in the direction of the displacement times delta s or, equivalently, the component of displacement in the direction force times F. It is evident that no work whatsoever is done by a force which is at right angles to the displacement." I have had the benefit of especially good and rigorous instruction in Physics, and I have long noted the religious storms that have swirled about the topic of "conservation of ____" (fill in the prayer book blank). I have also long noted the complete absence of any actual complete balance which necessarily requires both forms of energy, kinetic and potential. In fact, kinetic energy has seemed to be the uninvited guest to any discussion - treated as some poor relation consigned to the oblivion of consideration. If anyone is really pursuing the topic of fields and work, then they should at least visit the authority on the topic, Feynman, and read his chapters wholly devoted to the topic: 13 Work and Potential Energy (A) and 14 Work and Potential Energy (conclusion) and specifically: 14-5 Potentials and fields I include chapter 13 because within it, in a subordinate almost parenthetical aside, we find (on page 13-2) Power: "Because the concepts of kinetic energy, and energy in general, are so important, various names have been given to the important terms in equations such as these [referring to material preceding the statement]. F·v is called POWER: the force acting on an object times the velocity of the object (vector DOT product) is the power being delivered to the object by that force. We thus have a marvelous theorem: THE RATE OF CHANGE OF KINETIC ENERGY OF AN OBJECT IS EQUAL TO THE POWER EXPENDED BY THE FORCES ACTING ON IT." [emphasis in the original] Feynman is not generally available, but he is certainly held by many of those stumbling over the terms of their own invention. 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves, and other stupid notions
On Wed, 16 Jan 2008 09:30:35 -0800, Roger Sparks
wrote: =20 [snip] =20 ...Keith 73, Roger, W7WKB All this embedded markup makes it exceedingly difficult to read in a plain text reader for a plain text forum. 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves, and other stupid notions
Gene Fuller wrote:
Cecil Moore wrote: 1. Velocity of propagation, v = 1/SQRT(permeability*permittivity). 2. No electric or magnetic field in direction of propagation. 3. Electric field normal to magnetic field. 4. Value of electric field is the intrinsic impedance (ii) times the magnetic field at each instant. 5. Direction of propagation given by direction of ExH. 6. Energy stored in electric field per unit volume at any instant and any point is equal to energy stored in magnetic field per unit volume at that instant and that point. 7. Instantaneous value of Poynting vector given by E^2/ii = ii*H^2, where E and H are the instantaneous values of total electric and magnetic field strengths. [end quote] A standing wave doesn't satisfy any of those properties. By the way, a standing wave meets at least 5 of those 7 properties. 1. A standing wave doesn't propagate. From "Optics", by Hecht. "[A standing wave] doesn't rotate at all, and the resultant wave it represents doesn't progress through space -" 2. A standing wave doesn't propagate. 3. The electric field is either 0 or 180 degrees apart from the magnetic field. I proved that with math equations in an earlier posting which I invited you to disprove and you declined. Hint: see R&W quote below. The pure standing wave Poynting vector is known to be zero. The only way for that to happen (when E and H are both not zero) is for the E and H vectors to be mutually parallel, i.e. 0 or 180 degrees apart. 4. The ratio of electric field to magnetic field is not constant so it cannot be equal to the intrinsic impedance of the medium. 5. A standing wave doesn't propagate. 6. At any instant, at a point, all the energy may be stored in either electric or magnetic field while the other is zero. At the nodes, energy is never stored in one of the fields. 7. At a point where E=0, H will sometimes be maximum. Again, the intrinsic impedance is not the ratio of E to H. Sorry, 0 for 7. A standing wave is NOT a uniform plane wave. As Hecht said, it is questionable whether a standing wave deserves to be called a wave. Also from Ramo & Whinnery: "It is also instructive to consider the cases for which there will be no power flow through the electromagnetic field. Accepting the foregoing interpretation of the Poynting vector, we see it will be zero when either the E-field or H-field is zero, or when the two vectors are mutually parallel." see item 3 above. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
Jim Kelley wrote: I think he might have said it because he's not particularly good with words. If anything, he probably should have said that standing waves should just be called interference patterns. I'll buy that, Jim. I believe that Hecht left out the adjective, "EM". If he meant standing waves don't deserve to be called EM waves, I agree 100%. However, standing waves seem to meet the broad definition of "wave". I could be wrong, but don't E-fields and H-fields from traveling waves superpose to form net E-fields and H-fields? Wouldn't the net fields have vectors whose direction and magnitude are determined by the vectors which correspond to the traveling wave fields? Of course. Now try to convince Gene of that fact of physics. In spite of his earlier assertions about the differences between traveling waves and standing waves that agreed with my side of the argument, he seems to have switched sides. (For political reasons)? In the case of a radiator, the emanating energy is a result of the superposition of fields radiated by the currents traveling on the antenna. I could be mistaken, but it seems to me that superposition should yield the same result by either approach. If so, then for a single element radiator, the field pattern would appear as though a standing wave on the antenna had created the field. ac6xg |
Standing morphing to travelling waves, and other stupid notions
Roger Sparks wrote:
Having the assumption that energy does not pass the zero voltage point strikes at the heart of the traveling wave concept. I can not see what would reflect the waves to prevent energy passage at the zero voltage point, nor can I see a way to get the results we see between reflection points, if we disallow energy passage at zero voltage points. The medium at the zero voltage point is homogeneous. Nobody has produced a reference for or example of reflections occurring in a homogeneous medium. Until such evidence is introduced, it is probably safe to assume that reflections in a homogeneous medium in the real world are impossible (except in a human mind where anything is possible). -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Richard Clark wrote:
Roger Sparks wrote: All this embedded markup makes it exceedingly difficult to read in a plain text reader for a plain text forum. Just instruct Agent to display in plain text. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Jim Kelley wrote:
In the case of a radiator, the emanating energy is a result of the superposition of fields radiated by the currents traveling on the antenna. I could be mistaken, but it seems to me that superposition should yield the same result by either approach. If so, then for a single element radiator, the field pattern would appear as though a standing wave on the antenna had created the field. ac6xg The field created by any conductor is proportional to the current flowing on the conductor. You can divide this current into "forward" and "reverse" waves, or any combination of currents you want, just as long as they all add up to the total current. Assuming the conductor is immersed in a linear medium (e.g., air), you'll get exactly the same result by finding the fields from each of the individual currents you've chosen and adding them together, as you will by adding the currents first to get the total current and finding the field it creates. That's an example of the application of superposition. Roy Lewallen, W7EL |
Standing morphing to travelling waves, and other stupid notions
Jim Kelley wrote:
In the case of a radiator, the emanating energy is a result of the superposition of fields radiated by the currents traveling on the antenna. I could be mistaken, but it seems to me that superposition should yield the same result by either approach. If so, then for a single element radiator, the field pattern would appear as though a standing wave on the antenna had created the field. On a 1/2WL dipole, for instance, of the total amount of average energy existing on the antenna, approximately 80% of that energy is in the standing wave. The other 20% is radiated as real power presumably from the traveling waves because standing waves contain no real power. Like impedance transformation on a transmission line with reflections, the standing wave on the dipole is used to transform the relatively high Z0 of the antenna wire down to the relatively low feedpoint impedance of the antenna. The source re-supplies the radiated power to keep the average standing wave energy constant. Since the standing wave energy is being used to transform impedances, it cannot also be used for radiation purposes - like the energy in a standing wave on a transmission line cannot be used both to transform impedances and to heat up a load. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote: Since the standing wave energy is being used to transform impedances, it cannot also be used for radiation purposes - like the energy in a standing wave on a transmission line cannot be used both to transform impedances and to heat up a load. Would you care to elaborate on the idea that "energy is being used to transform impedances"? ac6xg |
Energy and Work
On Wed, 16 Jan 2008 18:53:44 -0500, "AI4QJ" wrote:
the wording in your statement above may need some modification such as: I think not. What this leads to is Cecilaboration that informs none of the discussion. This thread alone could turn into further amendments of what Feynman authored (and all scrambling to lay intellectual claim for his Oscar). Simple case in point, it may need some modification such as: 1. accounting for the force of viscosity; 2. accounting for the force of magnetism (ferro, para, and the rest); 3. accounting for the force of gravity; 4. accounting for the force of angular momentum; 5. accounting for the force of local tide; 6. accounting for the force of wind shear; 7. accounting for the force of advertising...... The arguments already filling the tea cup can't even raise the temperature for a decent brew. 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves, and other stupid notions
Jim Kelley wrote:
Cecil Moore wrote: Since the standing wave energy is being used to transform impedances, it cannot also be used for radiation purposes - like the energy in a standing wave on a transmission line cannot be used both to transform impedances and to heat up a load. Would you care to elaborate on the idea that "energy is being used to transform impedances"? If reflections are nonexistent, no transformation takes place, i.e. there is no SWR circle, just a point at the center of the Smith Chart and the system is flat. If reflections exist, then the superposition of the forward wave and reflected wave transforms the load impedance to some other impedance on the SWR circle. A 1/4WL transformer, for instance, will not transform unless there are reflections present. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Keith Dysart wrote:
So you seem to be claiming that the following two statements can be simultaneously true: 1. Power [recall p(t)=v(t)*i(t)] is the rate at which energy is transferred. 2. Energy can be transferred when the power is zero. To my simple intellect, one of these statements must be false. The second statement is an oversimplification - it switches between two inconsistent sets of boundaries. Energy is being transferred within the system as a whole, even though the power p(t) at some individual points within the system is zero. If you look consistently at the system as a whole, there are no contradictions. -- 73 from Ian GM3SEK |
Standing morphing to travelling waves, and other stupid notions
On Jan 17, 2:07*am, Ian White GM3SEK wrote:
Keith Dysart wrote: So you seem to be claiming that the following two statements can be simultaneously true: 1. Power [recall p(t)=v(t)*i(t)] is the rate at * which energy is transferred. 2. Energy can be transferred when the power is zero. To my simple intellect, one of these statements must be false. The second statement is an oversimplification - it switches between two inconsistent sets of boundaries. Energy is being transferred within the system as a whole, even though the power p(t) at some individual points within the system is zero. If you look consistently at the system as a whole, there are no contradictions. Expanding on statement 1) from above.... p(t) = v(t) * i(t) computes the power moving between two networks separated by the point at which v and i are measured. Expanding on statement 2... Cecil's claim is that the "energy in" the forward and reflected waves travel from end to end on the transmission line. Applying statement 1) to any point on an open circuited transmission line where the current or voltage is always 0 will yield a power that is always 0. Applying statement 2) to this same point yields that energy is crossing this point. This seems to me to be a definite contradiction between 1) and 2) for the specific situation under consideration. ...Keith |
Standing morphing to travelling waves, and other stupid notions
Keith Dysart wrote:
Expanding on statement 2... Cecil's claim is that the "energy in" the forward and reflected waves travel from end to end on the transmission line. The forward wave and reflected wave each possess energy and momentum which must be conserved. Assuming the transmission line is a homogeneous medium, i.e. a constant Z0, there is nothing anywhere along the line that can possibly cause a reflection. A reflection is necessary to reverse the momentum of a wave and reflections are impossible in a homogeneous medium. By the process of elimination, there must be something wrong with statement #1. This is easy to demonstrate on the bench using a TV signal. Even though there are points of zero power in the standing wave, ghosting will be clearly visible proving that the forward wave has made a round trip to the end of the stub and back. The superposition principle allows us to analyze the forward wave and reflected wave separately. When we do that, it is obvious that energy is flowing both ways across that zero power node location and at all other points on the line. If the reflected wave is equal in magnitude to the forward wave, the net power is zero at every point on the line, not just at the nodes. The Poynting vector for the forward wave is equal in magnitude and opposite in direction to the Poynting vector for the reflected wave. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
3. The electric field is either 0 or 180 degrees apart from the magnetic field. I proved that with math equations in an earlier posting which I invited you to disprove and you declined. Hint: see R&W quote below. The pure standing wave Poynting vector is known to be zero. The only way for that to happen (when E and H are both not zero) is for the E and H vectors to be mutually parallel, i.e. 0 or 180 degrees apart. Oops, I am afraid I must retract my previous congratulatory progress report. You are obviously still confusing phasors with field vectors. Until you get that terrible misconception sorted out, there is no hope for further progress. I assume that Hecht covers the equations and such. I am sure that Born and Wolf cover this subject in detail. Check out page 277 in the 6th edition or page 308 in the 7th edition. You will quickly observe that the H-field is always perpendicular (90 degrees) to the E-field, even for standing waves. There is no "0 or 180 degrees" involved. Is there anything else you plan to teach me about physics? There is still a whole lot I don't know. I think I may seek out another source, however. 8-) 73, Gene W4SZ |
Standing morphing to travelling waves, and other stupid notions
On 9 Jan, 19:27, Cecil Moore wrote:
On Jan 9, 3:13 pm, Jim Kelley wrote: On what page has Dr. Hecht written "a standing wave is a different kind of electromagnetic wave"? Since I didn't say that Dr. Hecht said that, it must be a rhetorical question. Here's what Dr. Hecht did say: In "Schaum`s College Physics Outline" by Bueche & Hecht on page 214 is written: "Standing Waves:....These might better not be called waves at all since they do not transport energy and momentum." (Thanks to Richard Harrison for that quote.) I agree with Dr. Hecht. Standing waves should not be called waves at all since they do not meet the definition and requirements for EM waves. I asserted that expression for the sum of traveling waves and the expression for the resulting standing wave pattern are related by trig identity, as per page 140 of the 28th Edition of the CRC Standard Mathematical Tables Handbook. Sorry Jim, that's not what you said. You asked if I recognized the trig identity that (presumably) equated a standing wave to a traveling wave. If that was not your meaning, it is time to say exactly what meaning I was supposed to assume. The 'wave' which stands is merely an amplitude envelope for the waves which move. Key word there is "waves". A standing wave is NOT self sufficient - it requires the superposition of a forward-traveling wave and a reverse- traveling wave. A standing wave loses its EM wave identity in the process of that superposition and apparently creates an illusion capable of mass hysteria. To alleviate that hysteria, one has only to compare the equations for standing waves and traveling waves or the corresponding graphs of those functions to see that they are hardly anything alike. -- 73, Cecil, w5dxp.com Cecil' How can one focus so long on travelling and standing waves when the radiation portion of the subject has not been explained? If waves is the subject it cannot be discussed coherently if you cannot describe the mechanism of radiation, and that subject is inexplicitely bound up with this whole discussion. All of this is pure conjecture based on what is happening behind a closed door which cannot continue until that door is opened. Only then will this discussion be revealed for what it truely is, which is all the things that could be happenning where the winner, if there is one,will be picked when the door is finally opened. Until then every thing is pure guess work. Best regards Art |
Standing morphing to travelling waves, and other stupid notions
Gene Fuller wrote:
Oops, I am afraid I must retract my previous congratulatory progress report. You are obviously still confusing phasors with field vectors. Until you get that terrible misconception sorted out, there is no hope for further progress. Let's skip your objection for the moment and let you answer this simple technical question. Poynting vector = ExH = E*H*sin(A) The Poynting vector for a pure standing wave = 0. It is always zero even when both E and H are not zero. So here is the question for you. Assuming that neither E nor H is equal to zero: When E*H*sin(A) = 0 (Poynting vector) What are the possible magnitudes of angle 'A'? This is a simple technical question having absolutely nothing to do with confusing phasors with field vectors. Please provide an answer. I assume that Hecht covers the equations and such. Yes he does. He also recognizes when the EH fields incident upon a plane can be validly represented by phasors. Apparently, Hecht also "confuses phasors with field vectors". (SIC) -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
art wrote:
How can one focus so long on travelling and standing waves when the radiation portion of the subject has not been explained? If waves is the subject it cannot be discussed coherently if you cannot describe the mechanism of radiation, ... The mechanism of radiation is pretty simple from a quantum electrodynamic standpoint. Accelerated electrons emit photons. Some of the photons escape the antenna. The energy lost by the escaping photons must be replaced by the source. QED. :-) Art, if you would replace electrons with photons in your blast-off theory, you will be closer to the facts. -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Gene Fuller wrote:
Oops, I am afraid I must retract my previous congratulatory progress report. You are obviously still confusing phasors with field vectors. Until you get that terrible misconception sorted out, there is no hope for further progress. Draw a plane through which a plane EM wave is passing normal to the plane. Now please explain exactly why the E-field and H-field cannot be represented by phasors. I posted this separately to keep from confusing simple issues with complex issues. Get it? Complex issues? :-) -- 73, Cecil http://www.w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
On 17 Jan, 09:51, Cecil Moore wrote:
art wrote: How can one focus so long on travelling and standing waves when the radiation portion of the subject has not been explained? If waves is the subject it cannot be discussed coherently if you cannot describe the mechanism of radiation, ... The mechanism of radiation is pretty simple from a quantum electrodynamic standpoint. Accelerated electrons emit photons. Some of the photons escape the antenna. The energy lost by the escaping photons must be replaced by the source. QED. :-) Art, if you would replace electrons with photons in your blast-off theory, you will be closer to the facts. -- 73, Cecil *http://www.w5dxp.com Thank you for your civil reply. What I am trying to say is that this long long thread has got a life of its own that it is excluding a lot of people. If it concentrated on say, a simple parallel circuit, a very simple circuit then the absolute physics of what is being discussed would be an immense help in explaining this wave discussion.ARRL states that an antenna is a simple parallel circuit but this concentration on antenna workings is blind siding every body as well as providing a means for twisting the discussion because the makings of radiation is not known. Why not illustrate waves in a simple parallel circuit so that observers can partake in this discussion which, if it ever comes to closure, could then be used to demonstrate their effect on radiation? Onlookers are more than willing to partake in the discussion but presently they are on the side lines because as presented it is limited to only those whose intent is to argue without obtaining closure and their feeding habits are insatiable as you are finding out. Best regards Art Unwin KB9MZ......XG |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
Gene Fuller wrote: Oops, I am afraid I must retract my previous congratulatory progress report. You are obviously still confusing phasors with field vectors. Until you get that terrible misconception sorted out, there is no hope for further progress. Let's skip your objection for the moment and let you answer this simple technical question. Poynting vector = ExH = E*H*sin(A) Incorrect. The Poynting vector is defined as E x H*. The vector directions are critically important. It is absolutely incorrect to try to reduce to some scalar type equation. (The '*' means complex conjugate, but this detail is not always important.) The Poynting vector for a pure standing wave = 0. Says who? Perhaps the time and space averages or "net", whatever that means, but not the local instantaneous Poynting vector. It is always zero even when both E and H are not zero. Nonsense. It is E x H* at every point. If E or H is zero then the Poynting vector is zero. Otherwise it will not be zero. So here is the question for you. Assuming that neither E nor H is equal to zero: When E*H*sin(A) = 0 (Poynting vector) What are the possible magnitudes of angle 'A'? This is a simple technical question having absolutely nothing to do with confusing phasors with field vectors. Please provide an answer. The answer is that you have started with incorrect equations. I assume that Hecht covers the equations and such. Yes he does. He also recognizes when the EH fields incident upon a plane can be validly represented by phasors. Apparently, Hecht also "confuses phasors with field vectors". (SIC) You have obviously misunderstood what Hecht is saying. A phasor does not carry any vector information. It is a representation of magnitude and phase angle only. That says absolutely nothing about the direction of the field vector. The phase angle is completely unrelated to the vector direction of the E-field and/or H-field. 73, Gene W4SZ |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
Gene Fuller wrote: Oops, I am afraid I must retract my previous congratulatory progress report. You are obviously still confusing phasors with field vectors. Until you get that terrible misconception sorted out, there is no hope for further progress. Draw a plane through which a plane EM wave is passing normal to the plane. Now please explain exactly why the E-field and H-field cannot be represented by phasors. I posted this separately to keep from confusing simple issues with complex issues. Get it? Complex issues? :-) Cecil, The phasor has nothing to do with spatial direction of the field vector. It has everything to do with the amplitude and the (wt-kx) term in the wave equation. (The 'x' is simply a distance measure in the propagation direction. It does not say anything about the field vector directions, since the fields are transverse to the propagation direction.) This is really, really basic E&M stuff. If you still disagree, then you are own your own. 73, Gene W4SZ |
Standing morphing to travelling waves, and other stupid notions
art wrote:
Why not illustrate waves in a simple parallel circuit so that observers can partake in this discussion which, if it ever comes to closure, could then be used to demonstrate their effect on radiation? This discussion, to a large extent, is concerned with the nature of RF waves. There are no RF waves in a simple parallel circuit. I posted a list of characteristics of an EM plane wave. A parallel circuit doesn't match those characteristics. -- 73, Cecil http://www.w5dxp.com |
| All times are GMT +1. The time now is 02:03 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com