| Topic: |
Science > Physics |
| User: |
"Peter peter21wilsonYahooCom" |
| Date: |
15 Dec 2004 09:09:08 PM |
| Object: |
Questions on electron transport in metals |
Hello:
I have a couple of questions on electron transport (in metals):
1. Consider a metal wire connecting the two terminals of a power
source. What exactly happens? Is it correct to say that electrons
behave as particles and flow in the wire at the drift velocity (v)
amidst random thermal motion to produce the required current? [I =
n*(-e)*v*A; I: current, n: free electron density, e: electronic charge,
A: cross section of the wire]
2. What exactly "makes" the electrons to flow? If it is the electric
field, what causes the electric field? Would it be correct to say that
the electrons at one end of the terminal have a higher ionization
potential compared to the other end and that the electric field is just
a convenient way to express this difference in the "potential energy"?
3. Don't electrons themselves, being charged particles, create an
electric field? Shouldn't the electrons so rearrange themselves to
counteract this external field and so stop the flow of current?
4. Does one terminal keep supplying electrons steadily into the wire to
prevent the stagnation of current as mention in Q3 above? If so, is
there a concentration gradient of electrons along the wire from the
source terminal to the drain terminal?
5. What happens if there is a bend in the wire? Shouldn't that affect
the field created by the electrons? Shouldn't it affect the current
flow? In other words will the following two structures have the same
resistance (assume they have the same total length):
S________________D
S____/\______D
S: Source , D: Drain
What, in particular, if the wire dimensions are comparable to the
electron mean free path?
6. I know that the energy of the electron in a metal (or in any
periodic lattice) is related to its momentum through the band
structure. How does this actually affect the particle picture of
electron flow in a metallic wire?
7. I know that, for low electric fields, wave packets of electrons in a
band can be considered to behave as particles obeying Newtons laws to
describe the time dependence of their (crystal) momentum. Please
correct me if my understanding is incorrect/incomplete.
Any answers to enlighten me will be sincerely appreciated.
Peter
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| User: "" |
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| Title: Re: Questions on electron transport in metals |
17 Dec 2004 01:26:40 PM |
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Peter <peter21wilsonYahooCom> wrote:
2. What exactly "makes" the electrons to flow? If it is the electric
field, what causes the electric field?
In other words, "Why does a battery produce a potential difference,"
or "why does a generator produce a potential difference," or "why does
a solar cell produce a potential difference," or ...
The answer is different for each. The reason for the e-field depends
on the type of energy source.
Would it be correct to say that
the electrons at one end of the terminal have a higher ionization
potential compared to the other end and that the electric field is
just
a convenient way to express this difference in the "potential
energy"?
Yes, a few electrons at one end of the wire were originally in a low-
energy state, and these electrons were removed. Electrons in a high-
energy state are placed at the other end of the wire. In some
respects
the long copper wire behaves as a single gigantic atom: electrons
in a high-energy location will travel to a low-energy location,
emitting
phonons as they do (and the wire becomes warm.)
3. Don't electrons themselves, being charged particles, create an
electric field? Shouldn't the electrons so rearrange themselves to
counteract this external field and so stop the flow of current?
Correct. The current exists in the wire BECAUSE the electrons are
trying to rearrange themselves. But no matter what the electrons do,
there is a charge-pump device which scoops electrons out of one end
of the wire, pushes them up into a higher-energy state, and deposits
them into the other end of the wire.
4. Does one terminal keep supplying electrons steadily into the wire
to
prevent the stagnation of current as mention in Q3 above? If so, is
there a concentration gradient of electrons along the wire from the
source terminal to the drain terminal?
Yes and yes. But note that, since electrons repel each other,
they will all move slightly in order to force the "region of electron-
imbalance" outwards. The electron-excess at the negative-charged
end of the wire will be found on the surface of the metal. The same
is true of the electron-deficeit on the positive-charged end.
5. What happens if there is a bend in the wire? Shouldn't that affect
the field created by the electrons? Shouldn't it affect the current
flow? In other words will the following two structures have the same
resistance (assume they have the same total length):
Yes, this is a major issue. It is treated in the paper I referenced in
my earlier message.
What, in particular, if the wire dimensions are comparable to the
electron mean free path?
In nano-sized semiconductors and in macro-sized vacuum tubes the
mean free path is long. The usual "circuit rules" break down in
both these situations. The electrons in a Klystron or in a CRT
behave very differently than in a resistor. The same is true of
"ballistic transistors."
6. I know that the energy of the electron in a metal (or in any
periodic lattice) is related to its momentum through the band
structure. How does this actually affect the particle picture of
electron flow in a metallic wire?
Except for explaining how resistors work, this issue is mostly ignored
in circuitry explanations. The velocity of electrons during an
electric
current is very low (they move like a clock's minute-hand!)
The energy which is being transferred by electric circuits is not
transferred by electrons, instead it is stored in the EM fields
surrounding the wires, and it does not travel within the metal.
There *is* some EM energy-flow within the metal, but it is directed
radially inwards as the external EM fields lose a bit of energy and
the metal is heated.
((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty(a)chem.washington.edu UW Chem Dept, Bagley Hall RM74
billb(a)eskimo.com Box 351700, Seattle, WA 98195-1700
ph206-543-6195 http//staff.washington.edu/wbeaty/
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| User: "Bob Masta" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 09:43:35 AM |
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On 17 Dec 2004 11:26:40 -0800, wrote:
6. I know that the energy of the electron in a metal (or in any
periodic lattice) is related to its momentum through the band
structure. How does this actually affect the particle picture of
electron flow in a metallic wire?
Except for explaining how resistors work, this issue is mostly ignored
in circuitry explanations. The velocity of electrons during an
electric
current is very low (they move like a clock's minute-hand!)
The energy which is being transferred by electric circuits is not
transferred by electrons, instead it is stored in the EM fields
surrounding the wires, and it does not travel within the metal.
There *is* some EM energy-flow within the metal, but it is directed
radially inwards as the external EM fields lose a bit of energy and
the metal is heated.
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Best regards,
((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty(a)chem.washington.edu UW Chem Dept, Bagley Hall RM74
billb(a)eskimo.com Box 351700, Seattle, WA 98195-1700
ph206-543-6195 http//staff.washington.edu/wbeaty/
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
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| User: "Franz Heymann" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 02:56:35 PM |
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"Bob Masta" <NoSpam@daqarta.com> wrote in message
news:41c44f7a.1431423@news.itd.umich.edu...
On 17 Dec 2004 11:26:40 -0800, wrote:
[snip]
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Not quite instantly.
The pressure you apply at the input end is propagated at the speed of
sound in the marble column
Franz
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| User: "" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 03:05:42 PM |
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Not quite instantly.
The pressure you apply at the input end is propagated at the speed of
sound in the marble column
It is? This seems very un-intuitive to me. Dont know why, it just seems
wrong. Sure, sound is vibration in a medium (?) so it kind-of makes
sense. I guess the speed of sound in very hard materials is very high?
---
John Bäckstrand
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| User: "Franz Heymann" |
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| Title: Re: Questions on electron transport in metals |
22 Dec 2004 04:43:44 PM |
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"John Bäckstrand" <newsmdhmajs.100.sandos@spamgourmet.com> wrote in
message news:41C49BA6.10907@spamgourmet.com...
Not quite instantly.
The pressure you apply at the input end is propagated at the speed
of
sound in the marble column
It is? This seems very un-intuitive to me.
That is irrelevant. It just means that you need to hone your
intuition.
{:-))
Dont know why, it just seems
wrong.
I would assure you in all sincerity that it is quite correct.
Sure, sound is vibration in a medium (?) so it kind-of makes
sense. I guess the speed of sound in very hard materials is very
high?
Yes. That is so.
Franz
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| User: "Androcles" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 07:52:56 PM |
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"John Bäckstrand" <newsmdhmajs.100.sandos@spamgourmet.com> wrote in
message news:41C49BA6.10907@spamgourmet.com...
Not quite instantly.
The pressure you apply at the input end is propagated at the speed of
sound in the marble column
It is?
Yep.
This seems very un-intuitive to me.
Can't think why. If you hit one end of a rubber rod with a hammer
will the other end move instantaneously?
Androcles.
Dont know why, it just seems
wrong. Sure, sound is vibration in a medium (?) so it kind-of makes
sense. I guess the speed of sound in very hard materials is very high?
---
John Bäckstrand
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| User: "" |
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| Title: Re: Questions on electron transport in metals |
19 Dec 2004 10:06:54 AM |
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Androcles wrote:
If you hit one end of a rubber rod with a hammer
will the other end move instantaneously?
Androcles.
No. The information propagates at the speed of sound, as others have
said. It is the same physical process as sound transmission: adjacent
atoms colliding or exerting force on each other.
As for electric signals, they propagate at the speed of light in the
medium. For a typical BNC cable, it's about 2/3 times c.
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| User: "Doug" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 05:05:26 PM |
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John Bäckstrand wrote:
Not quite instantly.
The pressure you apply at the input end is propagated at the speed of
sound in the marble column
It is? This seems very un-intuitive to me. Dont know why, it just seems
wrong. Sure, sound is vibration in a medium (?) so it kind-of makes
sense. I guess the speed of sound in very hard materials is very high?
---
John Bäckstrand
Speed of sound in various solids in m/s from a web stie. I made no attempt
to confirm
Diamond 12000
Pyrex glass 5640
Iron 5130
Aluminum 5100
Brass 4700
Copper 3560
Gold 3240
Lucite 2680
Lead 1322
Rubber 1600
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| User: "John Larkin" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 03:28:51 PM |
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On Sat, 18 Dec 2004 20:56:35 +0000 (UTC), "Franz Heymann"
<notfranz.heymann@btopenworld.com> wrote:
"Bob Masta" <NoSpam@daqarta.com> wrote in message
news:41c44f7a.1431423@news.itd.umich.edu...
On 17 Dec 2004 11:26:40 -0800, wrote:
[snip]
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Not quite instantly.
The pressure you apply at the input end is propagated at the speed of
sound in the marble column
That speed will, I think, be lower than the speed of sound in an
equivalent solid cylinder of glass. The marbles only touch at small
places, so the coupling is low. Dispersion will be terrible because of
the many random-ish paths (unless they're nicely lined up) so the
pressure pulse at the outlet will be very sloppy. The waveform should
be interesting.
John
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| User: "" |
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| Title: Re: Questions on electron transport in metals |
19 Dec 2004 10:17:06 AM |
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John Larkin wrote:
That speed will, I think, be lower than the speed of sound in an
equivalent solid cylinder of glass. The marbles only touch at small
places, so the coupling is low. Dispersion will be terrible because
of the many random-ish paths (unless they're nicely lined up) so the
pressure pulse at the outlet will be very sloppy. The waveform should
be interesting.
Probably right about the speed of sound being lower than for a solid
object. But, random paths don't necessarily make for sloppy waveforms.
Sound travels through randomized collections of molecules (like air)
just fine, as people are able to speak and hear each other clearly.
.
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| User: "Mike" |
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| Title: Re: Questions on electron transport in metals |
18 Dec 2004 12:34:36 PM |
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Bob Masta wrote:
On 17 Dec 2004 11:26:40 -0800, wrote:
6. I know that the energy of the electron in a metal (or in any
periodic lattice) is related to its momentum through the band
structure. How does this actually affect the particle picture of
electron flow in a metallic wire?
Except for explaining how resistors work, this issue is mostly
ignored
in circuitry explanations. The velocity of electrons during an
electric
current is very low (they move like a clock's minute-hand!)
The energy which is being transferred by electric circuits is not
transferred by electrons, instead it is stored in the EM fields
surrounding the wires, and it does not travel within the metal.
There *is* some EM energy-flow within the metal, but it is directed
radially inwards as the external EM fields lose a bit of energy and
the metal is heated.
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Did you try that? Your intiition fails when the marbles get stuck. You
need a lot of lubrication to perform you 'intuitive' analogy for long
pipes. In contrast, while resistance of wires may increase depending on
dimensions, there is always a finite current flowing and electrons
never get 'stuck'. Thus, your analogy is false. It has no connection
whatsover to current generation and flowing, a phenomenon that its
causes are still subject to hypothesis whilst its effects are detected
experimentally.
Mike
Best regards,
((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty(a)chem.washington.edu UW Chem Dept, Bagley Hall RM74
billb(a)eskimo.com Box 351700, Seattle, WA 98195-1700
ph206-543-6195 http//staff.washington.edu/wbeaty/
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
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| User: "" |
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| Title: Re: Questions on electron transport in metals |
19 Dec 2004 04:47:19 PM |
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Mike wrote:
Bob Masta wrote:
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Did you try that? Your intiition fails when the marbles get stuck.
You
need a lot of lubrication to perform you 'intuitive' analogy for long
pipes.
Simply use frictionless marbles in your thought-experiment.
Or, build a 20cm version, then pretend that no new effects will
arise when applied to a 20KM version.
In contrast, while resistance of wires may increase depending on
dimensions, there is always a finite current flowing and electrons
never get 'stuck'. Thus, your analogy is false.
Your argument is fallacious. If you try to prove that a model is
not an model, by showing that it's imperfect... instead you have
only proved that it's NOTHING BUT a model!
By definition, a model is different than the real-world phenomenon
being modeled. If in the situation where the model is used, the
differences are irrelevant, then the model works well.
If you don't like the "marbles" analogy, here is how to defeat
it. First look at the purpose of the model: to explain electric
circuits to children in a simple way. Then find places in which
the model fails at its task. If the "marbles" analogy gives
more misconceptions to children than it gives them understanding,
then the "marbles" model fails, and nobody should use it.
But if the model gives them major insights, yet gives little or
no misconceptions, then the model is EXCELLENT, and all its
imperfections are irrelevant.
On the other hand, if the same "marbles" analogy was being used
to teach physics grad students about the details of quantum
mechanics of metals, then it would be a bad model.
It has no connection whatsover to current generation and flowing,
Yes. Your point? Sound is not an EM wave. That's what "analogy"
means.
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| User: "Bob Masta" |
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| Title: Re: Questions on electron transport in metals |
19 Dec 2004 07:57:38 AM |
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On 18 Dec 2004 10:34:36 -0800, "Mike" <eleatis@yahoo.gr> wrote:
Bob Masta wrote:
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Did you try that? Your intiition fails when the marbles get stuck. You
need a lot of lubrication to perform you 'intuitive' analogy for long
pipes. In contrast, while resistance of wires may increase depending on
dimensions, there is always a finite current flowing and electrons
never get 'stuck'. Thus, your analogy is false. It has no connection
whatsover to current generation and flowing, a phenomenon that its
causes are still subject to hypothesis whilst its effects are detected
experimentally.
Mike, it was an *intuitive* example, just to get across the
concept that the speed of information (energy) travel can
be much faster than the speed of the individual carriers.
In that respect it is a very good analogy, because the
reasons in both cases are the same: Each marble pushes
on the one ahead of it, and the force is transmitted
"instantly". (I used quotes to avoid getting into the speed
of sound issue.)
To demonstrate this to kids, I use a piece of PVC about
a foot long, filled with black marbles. A long rubber band runs
from end to end and holds in the marbles. When you
push a marble in one end, you have to overcome the
resistance of the rubber. That aspect may have no
particular analog, but it cause the marble on the far
end to "pop" out of the pipe like magic. When kids
first see this, it fits with the idea that electricity is
instantaneous. I repeat this a few times until they
expect to always see a black marble pop out, but
I've secretly put a white marble a few positions down
the pipe. So when they see a black marble go in
and a white marble pop out, they "get" the idea
that it's not the *same* marble coming out. That's
a very important concept, and leads to a discussion
of the amazing fact that they could *walk* faster
than the electrons move in most ordinary situations.
They can understand that after understanding the
pipe analogy.
Best regards,
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
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| User: "Mike" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 04:35:20 AM |
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Bob Masta wrote:
On 18 Dec 2004 10:34:36 -0800, "Mike" <eleatis@yahoo.gr> wrote:
Bob Masta wrote:
A good intuitive example is a pipe full of marbles. If you push
another marble into one end, a marble on the far end moves
out "instantly", even though it is a long way away.
Did you try that? Your intiition fails when the marbles get stuck.
You
need a lot of lubrication to perform you 'intuitive' analogy for
long
pipes. In contrast, while resistance of wires may increase depending
on
dimensions, there is always a finite current flowing and electrons
never get 'stuck'. Thus, your analogy is false. It has no connection
whatsover to current generation and flowing, a phenomenon that its
causes are still subject to hypothesis whilst its effects are
detected
experimentally.
Mike, it was an *intuitive* example, just to get across the
concept that the speed of information (energy) travel can
be much faster than the speed of the individual carriers.
In that respect it is a very good analogy, because the
reasons in both cases are the same: Each marble pushes
on the one ahead of it, and the force is transmitted
"instantly". (I used quotes to avoid getting into the speed
of sound issue.)
To demonstrate this to kids, I use a piece of PVC about
a foot long, filled with black marbles. A long rubber band runs
from end to end and holds in the marbles. When you
push a marble in one end, you have to overcome the
resistance of the rubber. That aspect may have no
particular analog, but it cause the marble on the far
end to "pop" out of the pipe like magic. When kids
first see this, it fits with the idea that electricity is
instantaneous. I repeat this a few times until they
expect to always see a black marble pop out, but
I've secretly put a white marble a few positions down
the pipe. So when they see a black marble go in
and a white marble pop out, they "get" the idea
that it's not the *same* marble coming out. That's
a very important concept, and leads to a discussion
of the amazing fact that they could *walk* faster
than the electrons move in most ordinary situations.
They can understand that after understanding the
pipe analogy.
Best regards,
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Bob, I understand your point but my point is that at the end of the day
this type of analogies have an adverse effect in the minds of those
people, the majority that is, who do not understand the purpose of
modelling. It has the potential to create ellusive connections in the
minds of people and eventually turn them into cranks.
I insist this whole approach is wrong although well motivated. There
are discussions going on on this recently and the need to change the
whole approach to teaching physics.
The model you described is problematic, I think highly. It does not
demonstrate how 'information' travels faster than individual carriers.
Simply because there is no indication in your example what kind of
information is transmitted. The information cannot be the carrier
itself. If you try to actually transmit information, you will find out
that dynamics enter into the picture and analogies start failing. As an
example, ask a student to paint the incoming ball a color of his
choice. What color is the ball coming out the other way? If it's not
the same, the information was not transmitted faster than the speed of
individual carriers but exactly at the speed of those carriers, as you
will have to push in several balls until you get the collor one out.
Mike
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| User: "" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 09:21:08 AM |
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Mike,
The model you described is problematic, I think highly. It does not
demonstrate how 'information' travels faster than individual
carriers.
Simply because there is no indication in your example what kind of
information is transmitted.
The transmitted information could be the simple fact that a ball was
either pushed in at one end, or it wasn't. This **bit** of information
does travel faster than the individual carriers.
At any rate, it seems you're trying to take the analogy farther than
was meant. It was just suggested as a simple way to picture
electrons moving in a conductor. Obviously it is not meant for
any serious, quantitative study of electrical conduction.
-- Mark
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| User: "Bob Masta" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 08:06:09 AM |
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On 20 Dec 2004 02:35:20 -0800, "Mike" <eleatis@yahoo.gr> wrote:
Bob, I understand your point but my point is that at the end of the day
this type of analogies have an adverse effect in the minds of those
people, the majority that is, who do not understand the purpose of
modelling. It has the potential to create ellusive connections in the
minds of people and eventually turn them into cranks.
Mike, this isn't about modelling, it's about conveying a very basic
and simple concept to people (kids) who haven't encountered it
before.
I insist this whole approach is wrong although well motivated. There
are discussions going on on this recently and the need to change the
whole approach to teaching physics.
If you don't give them an intuitive grasp, they may never "get it".
You can't bombard them with all the gritty details right at the
start, or they will throw up their hands and give up. Instead, you
approach it somewhat like science itself progresses, by continually
refining the details. Works for me!
The model you described is problematic, I think highly. It does not
demonstrate how 'information' travels faster than individual carriers.
Simply because there is no indication in your example what kind of
information is transmitted. The information cannot be the carrier
itself. If you try to actually transmit information, you will find out
that dynamics enter into the picture and analogies start failing. As an
example, ask a student to paint the incoming ball a color of his
choice. What color is the ball coming out the other way? If it's not
the same, the information was not transmitted faster than the speed of
individual carriers but exactly at the speed of those carriers, as you
will have to push in several balls until you get the collor one out.
I think you missed the point about information. Information in
this case is the presence of "current flow". Consider the stub
of pipe to be a section of wire in a larger circuit that lights a
lamp. If the lamp is lit you have a binary '1' and if not it's a '0'.
Once a student understands the marbles-in-the-pipe concept,
s/he can understand that the speed of each electron marble
is not what determines how fast the lamp comes on when
you throw the switch... the information of the switch being
thrown travels *way* faster than the individual carriers.
That's all, nothing deeper, no relativistic mechanics, just
a single, basic, gut-level understanding that they won't forget.
Best regards,
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
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| User: "Mike" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 09:29:16 AM |
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Bob Masta wrote:
On 20 Dec 2004 02:35:20 -0800, "Mike" <eleatis@yahoo.gr> wrote:
If you don't give them an intuitive grasp, they may never "get it".
You can't bombard them with all the gritty details right at the
start, or they will throw up their hands and give up. Instead, you
approach it somewhat like science itself progresses, by continually
refining the details. Works for me!
I see it as a wrong approach. it has a leveling out effect. You treat
smart and less smart at the same level, you alienate those who have a
chance to get ahead by offering analogies everyone can understand.
The model you described is problematic, I think highly. It does not
demonstrate how 'information' travels faster than individual
carriers.
Simply because there is no indication in your example what kind of
information is transmitted. The information cannot be the carrier
itself. If you try to actually transmit information, you will find
out
that dynamics enter into the picture and analogies start failing. As
an
example, ask a student to paint the incoming ball a color of his
choice. What color is the ball coming out the other way? If it's not
the same, the information was not transmitted faster than the speed
of
individual carriers but exactly at the speed of those carriers, as
you
will have to push in several balls until you get the collor one out.
I think you missed the point about information. Information in
this case is the presence of "current flow". Consider the stub
of pipe to be a section of wire in a larger circuit that lights a
lamp. If the lamp is lit you have a binary '1' and if not it's a
'0'.
Once a student understands the marbles-in-the-pipe concept,
s/he can understand that the speed of each electron marble
is not what determines how fast the lamp comes on when
you throw the switch... the information of the switch being
thrown travels *way* faster than the individual carriers.
False statement. The speed of information in your example equals the
speed of the individual carriers. The input ball covers a distance d at
time t with average velocity d/t. The output ball comes out at the same
time t covering the same distance. The information is trasmitted at the
speed of the individual balls, whatever that speed v is. As a matter of
fact, every ball has the same speed while information is transmitted,
assuming perfect conditions.
What you really want to say is that speed of information is independent
of the lenght of the medium but depends only on the speed of the
individual carrier, whether electrons or marbles. That's something
totally different from what you have described but it turns out to be
false also in relaticistic limits.
This is the failure of your mechanical analogy, in which there is a
clear confusion between the speed of information and the speed of the
carrier which is d/t. These two are always equal, in mechanical systems
we can model this interaction but in electrical systems we have no idea
why this holds, only hypotheses. It is sad to try to enforce at that
early stage the concept that electrons are something like marbles, I
was subject to the same sin when I was a student and I am against such
absurdities, sorry to say.
I insist the losses are much higher than any gains when using such
analogies.
Mike
That's all, nothing deeper, no relativistic mechanics, just
a single, basic, gut-level understanding that they won't forget.
Best regards
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
.
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| User: "John Fields" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 11:31:54 AM |
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On 20 Dec 2004 07:29:16 -0800, "Mike" <eleatis@yahoo.gr> wrote:
Bob Masta wrote:
On 20 Dec 2004 02:35:20 -0800, "Mike" <eleatis@yahoo.gr> wrote:
If you don't give them an intuitive grasp, they may never "get it".
You can't bombard them with all the gritty details right at the
start, or they will throw up their hands and give up. Instead, you
approach it somewhat like science itself progresses, by continually
refining the details. Works for me!
I see it as a wrong approach. it has a leveling out effect. You treat
smart and less smart at the same level, you alienate those who have a
chance to get ahead by offering analogies everyone can understand.
---
Sounds like a great approach to me. If even the less gifted can
understand the analogy that certainly shouldn't deter the more gifted
from proceeding at their own pace, which they will. Would you
advocate analogies that only the more gifted understand?
---
The model you described is problematic, I think highly. It does not
demonstrate how 'information' travels faster than individual
carriers.
Simply because there is no indication in your example what kind of
information is transmitted. The information cannot be the carrier
itself. If you try to actually transmit information, you will find
out
that dynamics enter into the picture and analogies start failing. As
an
example, ask a student to paint the incoming ball a color of his
choice. What color is the ball coming out the other way? If it's not
the same, the information was not transmitted faster than the speed
of
individual carriers but exactly at the speed of those carriers, as
you
will have to push in several balls until you get the collor one out.
I think you missed the point about information. Information in
this case is the presence of "current flow". Consider the stub
of pipe to be a section of wire in a larger circuit that lights a
lamp. If the lamp is lit you have a binary '1' and if not it's a
'0'.
Once a student understands the marbles-in-the-pipe concept,
s/he can understand that the speed of each electron marble
is not what determines how fast the lamp comes on when
you throw the switch... the information of the switch being
thrown travels *way* faster than the individual carriers.
False statement. The speed of information in your example equals the
speed of the individual carriers. The input ball covers a distance d at
time t with average velocity d/t. The output ball comes out at the same
time t covering the same distance. The information is trasmitted at the
speed of the individual balls, whatever that speed v is. As a matter of
fact, every ball has the same speed while information is transmitted,
assuming perfect conditions.
---
I could be wrong, of course, but you seem to be an idiot. If a switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on. It's no more
necessary for the electrons at the switch end to traverse the entire
length of the wire before the lamp turns on and says, "The switch on
the other end is on" than it for a marble to fall out of one end of
the pipe with the information that a marble was pushed into the far
end of the pipe at essentially the same time as when the marble fell
out.
---
What you really want to say is that speed of information is independent
of the lenght of the medium but depends only on the speed of the
individual carrier, whether electrons or marbles. That's something
totally different from what you have described but it turns out to be
false also in relaticistic limits.
This is the failure of your mechanical analogy, in which there is a
clear confusion between the speed of information and the speed of the
carrier which is d/t. These two are always equal,
---
No, they're not. Consider the case where a different colored marble
is placed into one end of the tube and two questions are being asked
at the far end of the tube: "Was a marble stuffed into the tube?" and
"Was that marble a different color from the other marbles?" Both
questions deal with pieces of information, but the first can be
answered immediately while it will take some time to answer the second
one, and even when it does exit the tube there will be some question
as to what "that" marble refers to unless there was some agreed upon
protocol to be adhered to during the exercise.
---
in mechanical systems
we can model this interaction but in electrical systems we have no idea
why this holds, only hypotheses. It is sad to try to enforce at that
early stage the concept that electrons are something like marbles, I
was subject to the same sin when I was a student and I am against such
absurdities, sorry to say.
---
If you're against such "absurdities", then why are you sorry to say
so?
You seem to be saying that it's the map's fault that you can't tell
the difference between the map and the place the map is a picture of,
or blaming someone for having shown you the map in the first place...
---
I insist the losses are much higher than any gains when using such
analogies.
---
Your insistence doesn't make it true, but it does make it seem that
you're saying, "If only I hadn't been taught it that way, I'd
understand it."
--
John Fields
.
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| User: "Franz Heymann" |
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| Title: Re: Questions on electron transport in metals |
21 Dec 2004 05:56:51 AM |
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"John Fields" <jfields@austininstruments.com> wrote in message
news:fi0es0pubd3aigubl7tmroavtlln8io4hp@4ax.com...
[snip]
I could be wrong, of course, but you seem to be an idiot. If a
switch
is turned on at one end of a wire, then a lamp on the other end
will
start to turn on as soon as the switch is turned on.
No. A TEM wave, as would be the case if the source and the lamp are
connected by means of either a coaxial cable or a pair of wires
forming a parallel wire transmission line, is propagated by the speed
predicted byb Maxwello's equations. If the transmission line is in a
vacuum, that speed would be equal to c.
Franz
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| User: "Dominic-Luc Webb" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 12:38:06 PM |
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I could be wrong, of course, but you seem to be an idiot. If a switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on.
John (applies to all of us)
Profanity and insults are not acceptable. Further, some of your
remarks to me were purely argumentative. Those of us with PhDs
in the sciences are expected to know these things. If you really
want to split hairs, the calculations we discussed earlier are
indeed estimations, as YOU should know! Now you make further
attacks and accusations of others. Indeed, there IS in fact a very
brief time delay from when a switch is turned on, as YOU should
know, as a self proclaimed expert in the field!
I would think the goal of this newsgroup is to facilitate learning
of electronics at a basic level (i.e., sci.electronics.basics) for
those who are not formally educated in electronics. My training in
teaching from rather prestigious institutions did not cover the use
of profanity and insults as part of the teaching process and this
practice was frowned upon. Those who are learning are frequently
frustrated by things that they do not understand and (very often in
electronics) things that do not work as anticipated.
It should be self evident that any person offering advice or teaching has
an untold responsibility to accept that the person on the other end is
trying to learn. With good teaching, they ultimately become good teachers.
Insults and profanity are not part of that program, which is why I am
politely asking you to stop.
Dominic
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| User: "Androcles" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 01:01:18 PM |
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"Dominic-Luc Webb" <dlwebb@canit.se> wrote in message
news:Pine.LNX.4.44.0412201857100.32283-100000@uno.canit.se...
I could be wrong, of course, but you seem to be an idiot. If a
switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on.
John (applies to all of us)
Profanity and insults are not acceptable. Further, some of your
remarks to me were purely argumentative. Those of us with PhDs
in the sciences are expected to know these things. If you really
want to split hairs, the calculations we discussed earlier are
indeed estimations, as YOU should know! Now you make further
attacks and accusations of others. Indeed, there IS in fact a very
brief time delay from when a switch is turned on, as YOU should
know, as a self proclaimed expert in the field!
I would think the goal of this newsgroup is to facilitate learning
of electronics at a basic level (i.e., sci.electronics.basics) for
those who are not formally educated in electronics. My training in
teaching from rather prestigious institutions did not cover the use
of profanity and insults as part of the teaching process and this
practice was frowned upon. Those who are learning are frequently
frustrated by things that they do not understand and (very often in
electronics) things that do not work as anticipated.
It should be self evident that any person offering advice or teaching
has
an untold responsibility to accept that the person on the other end is
trying to learn. With good teaching, they ultimately become good
teachers.
Insults and profanity are not part of that program, which is why I am
politely asking you to stop.
Dominic
Endorsed. If it we not not so, 3.8 GHz processors would be mounted on
3.8GHz motherboards instead of 400 MHz units.
Androcles.
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| User: "John Fields" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 06:45:37 PM |
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On Mon, 20 Dec 2004 19:38:06 +0100, Dominic-Luc Webb <dlwebb@canit.se>
wrote:
I could be wrong, of course, but you seem to be an idiot. If a switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on.
John (applies to all of us)
Profanity and insults are not acceptable.
---
***** you. ;-) Perhaps they're not acceptable to _you_, but you aren't
the be-all and end-all or the arbiter of what's acceptable and what
isn't. If you don't like what I write and/or you don't like the way I
choose to write, then either ***** off or plonk me. Or not. It really
makes very little difference to me what you think or do.
---
Further, some of your
remarks to me were purely argumentative.
---
To _you_??? Did I ruffle your feathers in that 555 thread, dear boy,
and you vowed to, somehow, avenge your infallible self and now you've
decided to whine about it here since the other thread died?
---
Those of us with PhDs
in the sciences are expected to know these things.
---
Seems like _you_ managed to slip through the cracks, though...
Slap any old cap in there and then trim it up with any old pot and
don't even bother to look at the spec's because it's only a hobbyist
application? Buy 20% resistors or whatever you can find on the street
because you don't know how to order decent parts using your browser?
Your dissertation must have been based on stochastics with a sample
size of one and an expected yield of 1ppm which, serendipetously, got
you your diploma.
---
If you really
want to split hairs, the calculations we discussed earlier are
indeed estimations, as YOU should know!
---
You're wrong. The calculations are beautiful and exact. When reality
rears its ugly head, however, and process variables come into play,
errors are created which must be accounted for. Those errors are
specified as deviations from perfect behavior on the data sheet for
the device and must be taken into account when using that device.
---
Now you make further
attacks and accusations of others. Indeed, there IS in fact a very
brief time delay from when a switch is turned on, as YOU should
know, as a self proclaimed expert in the field!
---
A brief time delay from when the switch is turned on until when?
I don't think you can point to a post where I claimed to be an expert
about _anything_ , but yes, you're right about the delay. It's common
knowledge that the effect follows the cause and, in our universe, the
delay will be (enter your approximation here)
---
I would think the goal of this newsgroup is to facilitate learning
of electronics at a basic level (i.e., sci.electronics.basics) for
those who are not formally educated in electronics.
---
Wrong again, I think. Many of the neophyte supplicants to these
groups are only interested in obtaining the solution to a particular
problem and, once that solution is proferred, will never be heard from
again
---
My training in
teaching from rather prestigious institutions did not cover the use
of profanity and insults as part of the teaching process and this
practice was frowned upon. Those who are learning are frequently
frustrated by things that they do not understand and (very often in
electronics) things that do not work as anticipated.
---
Where did you take your degree, the university of stifle?
If, as an instructor, you're confronted with profanity in your
classroom, you need to recognize that that is the sound of
dissatisfaction with what you're trying to do or what those who employ
you are trying to do. If you want to maintain respect, then you need
to counter profanity with wit which strikes home.
---
It should be self evident that any person offering advice or teaching has
an untold responsibility to accept that the person on the other end is
trying to learn. With good teaching, they ultimately become good teachers.
Insults and profanity are not part of that program, which is why I am
politely asking you to stop.
---
Crap. The reason you're asking me to stop is because I threaten your
view of what you'd like the world to be like if I wasn't here to
challenge your view of what you'd like it to be like, your oyster.
--
John Fields
.
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| User: "Mike" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 01:44:15 PM |
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John Fields wrote:
On 20 Dec 2004 07:29:16 -0800, "Mike" <eleatis@yahoo.gr> wrote:
I could be wrong, of course, but you seem to be an idiot. If a
switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on.
Of course you are wrong and ad hominen (these two go together 100% of
the time). You are making unfounded assumption, a result of your poor
education and misunderstanding of the laws of physics and the
foundational problems of science, I hope you do not convey that to any
students.
There is no such thing as "as soon as". Every physical process exhibits
a time delay depending on its dynamics. Regardless, the maximum speed
of information transmission that satisfies causality is c. If you have
a small mind and to you a wire looks like a 3 feet long pipe full of
marbles you are a fool.
It's no more
necessary for the electrons at the switch end to traverse the entire
length of the wire before the lamp turns on and says, "The switch on
the other end is on" than it for a marble to fall out of one end of
the pipe with the information that a marble was pushed into the far
end of the pipe at essentially the same time as when the marble fell
out.
I think you are still playing marbles. Grow up and learn some games for
big kids. Newton skrewed up your minds, I mean whatever was there
looking like a mind.
The speed of information cannot exceed the speed of its carrier
otherwise you got causality problems. You confuse this with electrons
having to travel the whole wire. Obviously, you do not understand the
issue being discussed.
Mike
--
John Fields
.
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| User: "Bob Masta" |
|
| Title: Re: Questions on electron transport in metals |
21 Dec 2004 08:27:14 AM |
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On 20 Dec 2004 11:44:15 -0800, "Mike" <eleatis@yahoo.gr> wrote:
<snip>
The speed of information cannot exceed the speed of its carrier
otherwise you got causality problems. You confuse this with electrons
having to travel the whole wire. Obviously, you do not understand the
issue being discussed.
Mike, the speed of the carrier in a wire is the electron drift
velocity, which is ridiculously slow in "normal" cases. The
speed of information is close to the speed of light. That's
all I was trying to convey.
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
.
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| User: "Franz Heymann" |
|
| Title: Re: Questions on electron transport in metals |
21 Dec 2004 03:17:21 PM |
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"Bob Masta" <NoSpam@daqarta.com> wrote in message
news:41c8321d.1972342@news.itd.umich.edu...
On 20 Dec 2004 11:44:15 -0800, "Mike" <eleatis@yahoo.gr> wrote:
<snip>
The speed of information cannot exceed the speed of its carrier
otherwise you got causality problems. You confuse this with
electrons
having to travel the whole wire. Obviously, you do not understand
the
issue being discussed.
Mike, the speed of the carrier in a wire is the electron drift
velocity, which is ridiculously slow in "normal" cases. The
speed of information is close to the speed of light. That's
all I was trying to convey.
That is incorrect in detail. the quantity "c" is the phase velocity.
The speed of information transfer is the group velocity.
In free space, TEM waves are propagated without dispersion. In that
case both those velocities are c.
In a wave guide supporting a wave with a longitudinal component of
either E or H, those two velocities differ from one another and
neither of them is equal to c, even when the guide is evacuated.
Franz
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| User: "John Fields" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 02:23:33 PM |
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On 20 Dec 2004 11:44:15 -0800, "Mike" <eleatis@yahoo.gr> wrote:
John Fields wrote:
On 20 Dec 2004 07:29:16 -0800, "Mike" <eleatis@yahoo.gr> wrote:
I could be wrong, of course, but you seem to be an idiot. If a
switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on.
Of course you are wrong and ad hominen (these two go together 100% of
the time). You are making unfounded assumption, a result of your poor
education and misunderstanding of the laws of physics and the
foundational problems of science, I hope you do not convey that to any
students.
---
I suppose your "superior" education is the reason for the missing 'an'
between 'making' and 'unfounded' as well as the reason why you
couldn't grasp the reasoning behind Bob Masta's _excellent_ analogy.
---
There is no such thing as "as soon as".
---
Of course there is, and as soon as you realize it the better off
you'll be.
---
Every physical process exhibits
a time delay depending on its dynamics. Regardless, the maximum speed
of information transmission that satisfies causality is c.
---
You've obviously never heard of quantum entaglement?
---
If you have
a small mind and to you a wire looks like a 3 feet long pipe full of
marbles you are a fool.
---
And if you _can't_ visualize that, then I'd have to agree with you and
say that your mind is much more spacious than mine.
---
It's no more
necessary for the electrons at the switch end to traverse the entire
length of the wire before the lamp turns on and says, "The switch on
the other end is on" than it for a marble to fall out of one end of
the pipe with the information that a marble was pushed into the far
end of the pipe at essentially the same time as when the marble fell
out.
I think you are still playing marbles. Grow up and learn some games for
big kids. Newton skrewed up your minds, I mean whatever was there
looking like a mind.
---
And your profound knowledge of science comes from whom? Mister Ed?
---
The speed of information cannot exceed the speed of its carrier
otherwise you got causality problems. You confuse this with electrons
having to travel the whole wire. Obviously, you do not understand the
issue being discussed.
---
If you think that, then you obviously have problems with, among other
things, reading comprehension and semantics. Is English your first
attempt at acquiring language skills?
--
John Fields
.
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| User: "Sbharris[atsign]ix.netcom.com" |
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| Title: Re: Questions on electron transport in metals |
20 Dec 2004 05:06:56 PM |
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John Fields Dec 20, 12:23 pm show options
Newsgroups:
sci.physics,sci.physics.cond-matter,sci.physics.electromag,sci.electronics.basics
From: John Fields <jfie...@austininstruments.com> - Find messages by
this author
Date: Mon, 20 Dec 2004 14:23:33 -0600
Local: Mon, Dec 20 2004 12:23 pm
Subject: Re: Questions on electron transport in metals
Reply | Reply to Author | Forward | Print | Individual Message | Show
original | Report Abuse
On 20 Dec 2004 11:44:15 -0800, "Mike" <elea...@yahoo.gr> wrote:
John Fields wrote:
On 20 Dec 2004 07:29:16 -0800, "Mike" <elea...@yahoo.gr> wrote:
I could be wrong, of course, but you seem to be an idiot. If a
switch
is turned on at one end of a wire, then a lamp on the other end will
start to turn on as soon as the switch is turned on.
Of course you are wrong and ad hominen (these two go together 100% of
the time). You are making unfounded assumption, a result of your poor
education and misunderstanding of the laws of physics and the
foundational problems of science, I hope you do not convey that to any
students.
---
I suppose your "superior" education is the reason for the missing 'an'
between 'making' and 'unfounded' as well as the reason why you
couldn't grasp the reasoning behind Bob Masta's _excellent_ analogy.
---
There is no such thing as "as soon as".
---
Of course there is, and as soon as you realize it the better off
you'll be.
---
Every physical process exhibits
a time delay depending on its dynamics. Regardless, the maximum speed
of information transmission that satisfies causality is c.
---
You've obviously never heard of quantum entaglement?
COMMENT:
No "information" as the term is generally understood, may be
transmitted faster than light, via quantum entanglement. Information is
something unexpected that can be extracted from noise, and used to
produce clear causes and effects. If such causal information could be
transmitted faster than light, then it could be used to produced
effects which proceed causes, for certain reference frames looking at
events separated by space-like intervals in SR. This would lead to
paradoxes, because it would be possible to loop the system to make the
effect of a cause be, to interrupt the cause itself. Then, where would
the effect have originated, with no cause?
If you have an FTL transmitter of information, and the postulates of
relativity regarding light are correct, it's also quite easy to
construct instruments in which an event both happens and doesn't
happen, depending on the speed with which you pass it at zero distance.
As the event could be the detonation of a bomb, this is clearly
ridiculous. Thus, no FTL is possible.
Fortunately, in quantum entanglement, no information can be extracted
from a stream of bits until it is compared with the bit stream at a
distance, and the process of transporting the bits for later comparison
must proceed at the speed of light or less. Thus no FTL transmitters
can be made, and no causal paradox situations can be constructed.
SBH
.
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| User: "John Fields" |
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| Title: Re: Questions on electron transport in metals |
21 Dec 2004 05:34:02 AM |
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On 20 Dec 2004 15:06:56 -0800, "Sbharris[atsign]ix.netcom.com"
<sbharris@ix.netcom.com> wrote:
No "information" as the term is generally understood, may be
transmitted faster than light, via quantum entanglement. Information is
something unexpected that can be extracted from noise, and used to
produce clear causes and effects. If such causal information could be
transmitted faster than light, then it could be used to produced
effects which proceed causes, for certain reference frames looking at
events separated by space-like intervals in SR. This would lead to
paradoxes, because it would be possible to loop the system to make the
effect of a cause be, to interrupt the cause itself. Then, where would
the effect have originated, with no cause?
---
I don't see it quite like that. I believe that cause _always_ has to
precede effect, but just like supersonic flight is possible, C doesn't
necessarily have to be a limit. Cerenkov radiation is a good example
of the effect of superluminal travel and, while the speed of the
moving particle doesn't exceed C in vacuo, it does exceed C in the
material in which it's travelling.
---
If you have an FTL transmitter of information, and the postulates of
relativity regarding light are correct, it's also quite easy to
construct instruments in which an event both happens and doesn't
happen,
---
So the cat has to be either dead or alive _before_ you open the box?^)
---
depending on the speed with which you pass it at zero distance.
As the event could be the detonation of a bomb, this is clearly
ridiculous. Thus, no FTL is possible.
---
In _our_ frame, so it would seem. However, I believe that thought
travels FTL and I've devised an experiment to test that hypothesis.
Wanna hear about it?
---
Fortunately, in quantum entanglement, no information can be extracted
from a stream of bits until it is compared with the bit stream at a
distance, and the process of transporting the bits for later comparison
must proceed at the speed of light or less. Thus no FTL transmitters
can be made, and no causal paradox situations can be constructed.
---
Just the _fact_ that quantum entanglement enables action at a distance
is proof enough for me that, under certain circumstances, C is a
_lower_ limit.
--
John Fields
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| User: "Mike" |
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| Title: Re: Questions on electron transport in metals |
21 Dec 2004 11:35:48 AM |
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John Fields wrote:
---
You've obviously never heard of quantum entaglement?
---
OK, I get it now, I was wasting my time talking to a crank.
Bye crank.
Mike
--
John Fields
.
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| User: "John Fields" |
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| Title: Re: Questions on electron transport in metals |
21 Dec 2004 11:50:26 AM |
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On 21 Dec 2004 09:35:48 -0800, "Mike" <eleatis@yahoo.gr> wrote:
John Fields wrote:
---
You've obviously never heard of quantum entaglement?
---
OK, I get it now, I was wasting my time talking to a crank.
Bye crank.
---
Duckin' out, Mikey?
Good riddance!
--
John Fields
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