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Questions on electron transport in metals

B

Bob Masta

Jan 1, 1970
0
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
 
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
 
M

Mike

Jan 1, 1970
0
Bob said:
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.
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
 
J

John Fields

Jan 1, 1970
0
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?
---
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...
---
 
D

Dominic-Luc Webb

Jan 1, 1970
0
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
 
A

Androcles

Jan 1, 1970
0
Dominic-Luc Webb said:
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.
 
M

Mike

Jan 1, 1970
0
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
 
J

John Fields

Jan 1, 1970
0
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.
 
J

John Larkin

Jan 1, 1970
0
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. The power to the lamp travels somewhat slower, in the wire, than
c. Nothing, including information, can travel faster than c.

John
 
J

John Fields

Jan 1, 1970
0
No. The power to the lamp travels somewhat slower, in the wire, than
c. Nothing, including information, can travel faster than c.

---
Duh. C'mon John, do I have to include the velocity factor of the wire
and account for the inductance of the filament because it's wound and
all the rest of that crap?

We're talkin about a switch here, and the time it takes for an
electron entering the wire because the switch was closed to get to the
filament VS an electron already there starting to move through the
filament, and a tube with marbles in it, for goodness' sake.
 
J

John Larkin

Jan 1, 1970
0
---
Duh. C'mon John, do I have to include the velocity factor of the wire
and account for the inductance of the filament because it's wound and
all the rest of that crap?

Yes!

We're talkin about a switch here, and the time it takes for an
electron entering the wire because the switch was closed to get to the
filament VS an electron already there starting to move through the
filament, and a tube with marbles in it, for goodness' sake.

"Instantaneous" is sort of one of those absolute words that invites
contradiction. I can't see how you'd be doing a beginner (or anybody
else) a disservice to mention that the *electricity* (or the push
through the marbles) travels at a finite speed, much faster than the
carriers.

John
 
S

Sbharris[atsign]ix.netcom.com

Jan 1, 1970
0
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 <[email protected]> - 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
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John Fields wrote:


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
 
J

John Fields

Jan 1, 1970
0
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 piss 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.
---
 
J

John Fields

Jan 1, 1970
0
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,
 
F

Franz Heymann

Jan 1, 1970
0
[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
 
F

Franz Heymann

Jan 1, 1970
0
John Larkin said:
No. The power to the lamp travels somewhat slower, in the wire, than
c. Nothing, including information, can travel faster than c.

Have you ever seen a proper proof of that statement, or are you just
repeating what you have been told, or have read?
I ask the question quite seriously.

Franz
 
R

Roger Johansson

Jan 1, 1970
0
Have you ever seen a proper proof of that statement, or are you just
repeating what you have been told, or have read?
I ask the question quite seriously.

Which statement, the first or the second?

The first is easy to prove with modern test equipment.

The second might be a bit more complicated to prove, as it involves the
whole basis for physics in general.
 
B

Bob Masta

Jan 1, 1970
0
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
 
J

John Larkin

Jan 1, 1970
0
Have you ever seen a proper proof of that statement, or are you just
repeating what you have been told, or have read?
I ask the question quite seriously.

No, I'm just a simple engineer; I believe what the physicists tell me.
If you know of a counter-case, we'd all like to hear about it.

John
 
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