Re: rotating magnetic field




+ADw-phil-news-nospam+AEA-ipal.net+AD4- wrote in message news:gvitah01gv5+AEA-news1.newsguy.com...
+AD4- On Tue, 26 May 2009 12:21:52 -0700 Don Kelly +ADw-dhky+AEA-shaw.ca+AD4- wrote:
+AD4-
+AD4- +AHw- If you are looking at the internal voltage E as measurable on open +AD4- circuit
+AD4- +AHw- and then for a current I, write Z+AD0-E/I you have now defined a useless +AD4- term
+AD4- +AHw- which can tell you nothing. In order to find the current, you do need to +AD4- use
+AD4- +AHw- E as well as the series impedance of the machine, line and load (which,
+AD4- +AHw- except for purely RLC may also not obey Ohm's Law).
+AD4- +AHw- Once you have found the current-then you can find this Z- why? it gives +AD4- no
+AD4- +AHw- useful information (and apparently it gives you
+AD4- +AHw- isinformation). --------------
+AD4-
+AD4- Any time you are talking about certain ratios, you are talking about +AD4- certain
+AD4- things. When you are talking about the ratio between distance and time, +AD4- you
+AD4- are talking about velocity. When you are talking about the ratio between
+AD4- energy and time, you are talking about power. When you are talking about +AD4- the
+AD4- ratio between voltage and current, you are talking about impedance (or if +AD4- you
+AD4- prefer, resistance). This is just part of the basics of understanding +AD4- units
+AD4- and systems of measure.
-------------
Sure, the term impedance can be used because the units are such, but it is not meaningful. You don+AGA-t have such an impedance. What you have is a voltage source behind some finite resistance connected to a load through some finite impedance. The load impedance may be anywhere from 0 to infinity.
So you have a fundamental equation E +AD0-Zi+ACo-I +-Zl+ACo-I +-ZL+ACo-I and knowing E and the impedances (which are all measurable) you can find I. You have nowall the information that you need. None of this infinite line nonsense. Dividing by I puts both sides in an +AGAAYA-impedance+AGAAYA- form but no more useful information is obtained. So you have a Z that varies with load and is of no use for finding the load current or system voltages.
Sure you can then write Zs+AD0-Zi+-Zl+-ZL which is the total external impedance seen by an ideal voltage source- lovely-but it serves absolutely no purpose that is not served by the original expression. If high or low it simply means that the total external impedance is high or low and doesn+AGA-t indicate anything about the relative values of the internal, line and load impedances-all that you have is a useless and nonsensensical term.
-------
+AD4-
+AD4- Have you ever just sat and thought about what E+AD0-mc+AF4-2 means as units? A +AD4- lot of
+AD4- people think it absurd to think about a velocity squared. But, in fact, +AD4- it
+AD4- makes complete sense once you try to understand what this really is in +AD4- terms
+AD4- of its units. Compare this to the formula for kinetic energy. See a +AD4- pattern?
+AD4- See a relationship? Can you see a meaning in the difference (more +AD4- correctly,
+AD4- the ratio)?
--------
The only relationship is that both express energy in Joules. So does mgh and E+ACo-I+ACo-time and f+ACo-x (force times distance), B+ACo-H for a magnetic field , etc etc etc. While they all express energy there is no pattern as they deal with different forms of energy.

+AD4- I don't worry about numbers so much. I think about the relationships +AD4- between
+AD4- the units. This is the basis of existance+ADs- not the numbers (or the +AD4- arbitrary
+AD4- scales of the units).
-----
I realize that you don+AGA-t want to deal with numbers but relationships between units can also lead you astray. In this case, as well as the energy relationships, it has done so. What you want to know is the fundamental concepts that are behind the whole thing and this is where you have a problem.
Case closed,

--
Don Kelly
dhky+AEA-shawcross.ca
remove the x to reply
+AD4-
+AD4- -- +AD4- +AHw-WARNING: Due to extreme spam, googlegroups.com is blocked. Due to +AD4- ignorance +AHw-
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+AD4- +AHw- Phil Howard KA9WGN (email for humans: first name in lower case at +AD4- ipal.net) +AHw-

.

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