W5DXP wrote:
wrote:
So when I use my voltmeter to measure a voltage, I actually have
two voltages present which sum to the reading.
Yes, that's why you need a directional voltmeter or directional
wattmeter to separate the forward wave from the reflected wave
when reflections exist.
When I do this on a D-cell, what are these two voltages?
Reflected voltage is zero during DC steady-state.
But how did you know this little cylinder with a bump on the
end produced DC? And why can't DC circuits have net voltages
derived from superposition? Seems that in your model you need
extra information before you know what your voltmeter is telling you.
I observe that you did not provide an answer for the other examples.
What about that power plug on the wall? Too difficult?
Feel free to assume that you own an abstract voltmeter which will
tell you the voltage as a function of time (an oscilloscope maybe?).
It would seem that this belief will lead to some serious decidability
issues.
If standing waves exist, there is one forward wave component and one
reflected wave component. If standing waves do not exist, there is
no reflected wave component. Shirley, you can tell whether standing
waves exist or not so you will know whether you are dealing with one
or two waves.
And don't ever trust your voltmeter again.
Do you use a DC voltmeter to measure AC? Do you use a 60HZ AC voltmeter
to measure 1 GHz RF voltages? Do you use a 100MHz o'scope to look at
a light wave?
Since we are discussing the world of the ideal, we can assume the
existence of ideal voltmeters.
If reflections exist and you are using a non-directional voltmeter, you
will read the NET voltage. USE THE APPROPRIATE MEASURING INSTRUMENTS!
So I will rephrase my question for your benefit:
When we measure a voltage using an ideal voltmeter, how do we know if
this voltage is composed of components (I generalize, since similar
difficulties arise in situations without reflections) so that we can
do extra measurements and computations to learn the 'real' voltages
and 'powers'?
If you wish, the wall outlet provides an excellent opportunity for
explanation by example.
....Keith