Re: Einstein's Doppler equation wrong?

From: Androcles (dummy_at_dummy.net)
Date: 10/31/04 

Date: Sun, 31 Oct 2004 15:27:55 GMT

"sal" <pragmatist@nospam.org> wrote in message
news:pan.2004.10.31.02.51.53.84314@nospam.org...
: On Sat, 30 Oct 2004 03:19:49 +0000, Androcles wrote:
:
: >
: > "sal" <pragmatist@nospam.org> wrote in message
: > news:pan.2004.10.30.02.22.31.661633@nospam.org...
: > : Just a few odds and ends.
: > :
: > : On Thu, 28 Oct 2004 13:13:26 +0000, Androcles wrote:
: > :
: > : > "sal" <pragmatist@nospam.org> wrote in message
: > : > news:pan.2004.10.28.01.58.30.58603@nospam.org...
: > : > : On Wed, 27 Oct 2004 22:07:57 +0000, Androcles wrote:
: > : > :
: > : > :
: > : > : > : If pressure impulses in air did that, we wouldn't be
able to
: > : > : > : understand each other when we talked!
: > : > : >
: > : > : > They do. An organ pipe resonates.
: > : > :
: > : > : That's not _quite_ the same effect, though, I think.
: > : >
: > : > I'll refer you to Christiaan Huyghens. Take ANY point ...
: > :
: > : Hmmm .... you may be right. This deserves more thought than I'm
: > likely to
: > : give it...
: >
: > Well, give thought to this.
: > 'j' is used as the sqrt(-1) to avoid confusion with 'i' which
represents
: > current, and you've done a pretty good job at confusing it. 'j' is
NEVER
: > current.
:
: Right -- it's current _density_, not current. Here are a couple of
: references; I'm just quoting the definitions, but trust me, I'm not
"quote
: mining" here:
:
: Griffiths, Intro to Electrodynamics, p. 212, second paragraph
:
: " ... we describe it by the volume current density, J, defined as
: follows..."
:
: This J, the volume current density, is the J in Maxwell's equations,
which
: are also discussed at length in Griffiths.
:
: Purcell, Electricity and Magnetism (from the Berkeley Physics
Series),
: inside back cover where the units are defined:
:
: ...
: CURRENT DENSITY J (esu/sec)/cm^2, defined by I = integral(J da)
: ...
:
: Purcell's definition makes it more explicit that I is current, and J
is
: current density.
:
: Dorf, The Electrical Engineering Handbook, CRC Press, 1993, page
1132,
: under "Dielectrics and Insulators", second paragraph,
:
: " ... sigma is equal to the leakage current density J_l ... "
:
: Finally, I'll mention that this is not universal -- some texts use I
for
: the current density. But it seems to be very common. Of the first
four
: places I looked, three of them used J for current density; the
fourth used
: I.
: Again, Maxwell's equations have a J in them, but it's current
density.
: There are no imaginary numbers in dear old Maxie.
:
: If you prefer to go on believing otherwise, without looking it up to
: actually check the definitions of the symbols in any textbook that
lays
: them out, I can't very well change your mind, of course. I know
perfectly
: well you won't be convinced by quotes I choose. :-)
:
I prefer to go on believing otherwise.
I = E/R --- Ohm.
That defines 'I' to my satisfaction, even if not yours.

In an RC circuit with DC applied as a step, current is maximized when
the voltage is zero, i.e dE/dt is at its greatest, and ceases when the
capacitor is fully charged, i.e. when dE/dt = 0.

o-------\/\/\/\/------o------||-------o
                      <-------E------->

There is volt drop E = IR across R, the capacitor is effectively a
short circuit. It becomes (after time has elapsed) an open circuit and
the volt drop across R is zero.

In an RL circuit with a DC step applied, the current is zero when the
voltage is first applied, dE/dt = is at its greatest, and is maximized
(to become steady DC which means for Direct Durrent) when dE/dt = 0.

o-------\/\/\/\/------o-----()))-----o
                      <-------E------->

There is volt drop across L, the coil is effectively an open circuit.
It becomes (after time has elapsed) a short circuit and the volt drop
across R is E = IR.

In an LC circuit at resonance, (no R) the voltage at the mid-point of
L and C lags the voltage across LC by pi.

o-------| |------o-----()))-----o
                 <-------E------->

Apply a step voltage to this circuit and it will ring, just as a bell
will when struck with a clapper. Just as a mass suspended on a spring
will oscillate.
Just as your car will when you go over a bump. That's why it is fitted
with
dampers misnamed "shock-absorbers" and if you want to misname
I = current you are using what Newton would call "vulgar" terminology.

I do not need to go quote mining on the internet.
I = E/R. --- Ohm.

To suggest that Maxwell did not know this is an affront to Jimmy
Clerk.
I can't very well change your stubborn mind, of course, but staring at
equations you do not fully understand is no comparison to direct hands
on experience.
Where did you not learn physics?

: > I agree with Maxwell, and Maxwell says the current is phase
shifted,
: > leading 90 degrees from the voltage, whatever the assistant
professor, the
: > fumble mumbler, yourself or anyone else says. Say "uncle":-)
: >
: >
: > : [ ... ]
: > :
: > : > :[SAL, on transmission line echoes:]
: > :
: > : > : Again, it's the bounce from the end that gives the echoes.
: > Terminate
: > : > : it properly, so there's no "bounce", and the signal comes
out
: > the
: > : > : other end perfectly "clean".
: > : >
: > : > I disagree. I consider there to be two boundaries, one at each
: > end, with
: > : > a resonant standing wave between antenna and "resistor". In
: > reality we
: > : > do not use a resistor anyway, we use an impedance. That is
known
: > as
: > : > "terminating properly". Just because the units of impedance
are
: > the same
: > : > as the units of resistance does not imply a terminating
resistor
: > is
: > : > employed.
: > :
: > : Ever done anything with ethernet, using the old thinnet drop
cables?
: > If
: > : you unplug the computer, you _must_ plug in a terminator in its
: > place (or
: > : somebody from network operations comes and yells at you). The
: > terminator
: > : consisted of a connector with a small resistor tying the core
and
: > shield
: > : of the coax together. At least in the ones I've seen, it really
was
: > just a
: > : simple resistor; I think it was either 50 or 75 ohms.
: > :
: > : Without the terminator, the thinnet cable spits back echoes into
the
: > : network, and the whole segment either goes dead or gets really
slow
: > as a
: > : result of errors and "ghost" collisions. With the terminator,
: > packets run
: > : down to the end of the cable and just vanish.
: > :
: > : A dead short at the end would act just like an open, as far as
: > scrambling
: > : the network goes, except that the echoes would come back
"reversed",
: > with
: > : the voltage inverted versus the outbound signal.
: > :
: > : (The vampire taps didn't have the same problem, of course --
pull
: > out the
: > : needle and you're all set, no terminator required.)
: > :
: > : Similarly, a SCSI bus needs to be terminated to avoid echoes.
: > Nowadays
: > : the termination is active and involves a hunk of circuitry. In
the
: > "old
: > : days", fifteen years ago, passive terminators were typically
used:
: > it was
: > : just a resistor pack, plugged onto the second SCSI connector on
the
: > last
: > : device in the chain. (I don't know what the values were.)
: >
: > Something needs looking into, because a 100 kW transmitter doesn't
use a
: > resistive load, the signal still goes up a pipe to the antenna at
the top
: > of a ruddy great tower and we are talking about the same frequency
as the
: > receiver is tuned to.
:
: Well, sure -- a resistive load would melt! :-)

Engineers know how to prevent that.
Ever heard of wire wound resistors? Tungsten has a high melting point.
You can make it glow white hot without melting.
Lighthouses are towers that are used for communication using
radiation.
It's an older technology that will be revived for interplanetary comms
later, once the light accelerator has been constructed. No funding for
it is available for it yet, people still believe Einstein's silly
statement about the velocity of light in a vacuum being independent of
the motion of the source,
and those with the capital to develop such a device trust the word of
the faithful.

You can quite effectively terminate the coax with a suitable LC
and lose nothing as heat in the resistor. However, because the
frequencies of digital signals are irregular, a resistor is a
compromise
to dampen the ringing, just a so-called "shock absorber" fitted to a
car
is a compromise. We have no idea what the frequency of bumps
in the road will be, but I COULD arrange resonance as an experiment.
The main shock absorbers are the tyres, backed up by the springs. The
dampers are the resisitive "shock absorbers".

:
: The current and voltage are in phase going into the antenna and the
power
: goes out into the aether ... ER oops I mean onto the air ... anyway
it
: goes away from the antenna.

When the current is running up the antenna it is charging a capacitor,
the "plates" of which are the top and bottom of the rod. dE/dt is at a
maximum
when E = 0. dI/dt = 0 when the current is maximized.
In the factory, we want to PREVENT radiation and utilize the energy as
motion.
In the broadcasting studio we want to radiate the energy and lose
nothing as heat.
One is the opposite of the other.

:
: With the ethernet and SCSI examples, I was just pointing out a
couple
: cases where a resistive load is used.

In your SCSI you do not care about the losses to heat. It is of no
significance. If you have ringing in a cable, damp it. Waste the
energy.
Engineering is always a compromise.

:
: > 50 ohms resistance at 100 kW is gonna be a stinking
: > hot coil of metal radiating 100 kW of heat, not FM, whichever end
of the
: > pipe you place it, and your reciever had better be close to the
tower,
: > not 100 miles away. Where is that current going? Up one side of
the pipe
: > and down the other.
: >
: > Capacitors are added to inductive loads in industry to reduce
current in
: > the cables and switchgear leading to the motors.
:
: Right -- the caps get the current back in phase with the voltage, so
it's
: actually doing something useful rather than just heating the wires.
Don't
: they use something like that in long transmission lines, too?

Coax is a "long" transmission line. :-)

:
: > Motors use minimum
: > resistance or energy is wasted as heat.
:
: >
: >
: >
: > : [ ... ]
: > :
: > : > Kitchen science:
: > : > Add a few drops of vegetable oil to a saucer of water, then
add
: > dish
: > : > washing liquid and watch what happens.
: > :
: > : I think I know the answer but I may try it anyway.
: > :
: > : > Here's another. Dice a carrot and potato. Mix. Now separate
the
: > carrot
: > : > from the potato. No, not by hand. Do it the easy way.
: > :
: > : Uh .... Drop them in a bowl of water, and one of them will float
but
: > not
: > : the other?
: >
: > Yep. Carrots float. Potatoes sink.
: > Just thought you might like to amuse your youngster.
: > Salt and sand, of course, everyone knows that one.
: >
: >
: > : If that doesn't work, offer the whole mess to a rabbit. After a
: > while
: > : only the potato will be left on the plate.
: > :
: > : If it's not either of those then I really don't know.
: > :
: > :
: > : --
: > : I can be contacted through http://www.physicsinsights.org
: > :
: > :
:
: --
: I can be contacted through http://www.physicsinsights.org
:

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