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Cecil Moore wrote:
John Popelish wrote: Cecil Moore wrote: That is not what the formula says. Pick and X and you get a constant phase angle with respect to the zero degree reference. But that phase angle is not zero as it is for standing waves. You seem to be talking in circles. How can the phase shift between the traveling wave and the source reference ever be zero at a point 90 degrees away from the source? I said the phase was was fixed, not zero, at a given position. If it cannot, then you have evidence that the traveling wave is NOT identical to the standing wave as evidenced by their different equations. I agreed that the pattern of amplitude and phase is different along a line for traveling and standing waves. But at any given point, there is a very similar kind of phasor ( one with an amplitude value and a phase value) that describes what is happening at that point. That difference in amplitude distribution and phase shift with respect to position is what the two functions describe. You keep claiming that there is something fundamentally different about the kind of phasor describing a single point (rotating versus non rotating), depending on whether the phasor is describing a point on a standing or traveling wave. That is where we disagree. Let's cut to the bottom line. You seem to believe that standing wave current is identical to traveling wave current. At a point, it certainly can be. How current varies (amplitude and phase) over length is what is different. If that's your point, just say so. I have said so as emphatically as I can, at least a half dozen times. You keep saying I am wrong and refer to rotating phasors and non rotating phasors. The only rotating phasor I know if is when a different (from the reference frequency and phase) frequency is described by phasor notation. That phasor rotates. Otherwise, please tell us the difference between the standing wave current and the traveling wave current which seems obvious to me from the equations. I have, already. But here goes once again. A current produced by a traveling wave has a constant (RMS) amplitude along the line. The phase of the current (relative to some arbitrary phase reference) varies linearly along the line. If the line is a wavelength or more long, you can find any relative phase you want, just by moving along the line. There is energy moving along the line during this process, but no net (averaged over a cycle) current moving along the line. this is similar to how wave energy moves along the surface of water, without the water traveling along with the wave. The water just moves up and down as the wave passes along its surface. Likewise, charge moves back and forth, locally, within a half wavelength of the line as the wave passes, and the local current is a measure of the rate of this charge movement. In the case of a pure standing wave, you have the super position of two equal and opposite traveling waves. The current (RMS) magnitude can vary anywhere from zero to twice the (RMS) magnitude of that produced by either of the two traveling waves. The RMS amplitude envelope will vary in a [absolute value of sine] way along the line. The relative phase of the current will have one of two values (the actual angle depending on what phase is chosen as the reference) that are 180 degrees apart. The phase switches between these two values each time you pass through a node in the amplitude distribution. There is no net energy movement, since the movement in one direction is canceled by energy movement in the other direction. There is, however, energy storage on the line. Since the charge movement in a standing wave is the superposition of the charge movement of two traveling waves, in a standing wave, charge also moves back and forth only within a half wavelength interval of the line. And the standing wave current is the measure of the rate of change in this charge movement as it sloshes back and forth within that half wavelength. If you have any corrections to any of this, please quote enough of what you what you are correcting for the context to be clear, and have at it. I want to get this right. |
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