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path of least resistence
|
|
| conrad 2007-04-20, 8:25 pm |
| What happens at the atomic level
where electrons have an affinity for
a path of least resistance? Imagine this,
you have a parallel circuit. And at the node
where the branching takes place, current can
flow down one branch(where a resistor exists)
and it can flow down the second branch(where
we have a short). Why does the majority of the
current go down the path where we have a short?
It isn't like electrons can forecast which path has
least resistence, right? So how does the principle
'follows path of least resistence' hold? Even when
measurements are taken, it can be observed that
the majority of current goes down the least resistive
path. It just doesn't make much sense when you
know electrons cannot forecast whether a resistor
or short lies ahead down one of the branches.
--
conrad
| |
| Androcles 2007-04-20, 8:25 pm |
|
"conrad" <conrad@lawyer.com> wrote in message =
news:1177117373.550034.231180@p77g2000hsh.googlegroups.com...
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short).=20
Are you dumb?
"The earth, newly turned, looked dark and rich, like crumbs of=20
chocolate cake. A few worms and wood lice had been disturbed
and were still looking for their old homes." -- Ian Rankin.
> It isn't like electrons can forecast which path has
> least resistence, right?=20
The word is "resistAnce", and yes, electrons do not have foresight.
> So how does the principle
> 'follows path of least resistence' hold?=20
Force.
I refuse to nitpick semantics here. Accept it or leave.
| |
|
|
conrad wrote:
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
Hey Conrad, the problem is you just don't understand the advanced
principles of modern quantum physics! The answer is that electrons
exist and don't exist at the same time. And even though the current is
split in two directions each electron can only go down one path at a
time. But the probability waves they create go down both paths at
once. And even though electrons can travel nearly as fast as light,
the possibility waves look way ahead and decide which is the
"best" (most probable) way to go. The problem is that you are trying
to think of electrons as particles when they are really waves and
trying to think of them as waves when they are really particles. Fact
is they are both and neither at the same time, as every "modern"
physicist knows full well. There. Are things clear now?
We'd like to say more, but until you learn to spell "resistence" and
master the secret handshake, the above explanation will have to do!
Benj
| |
| MassiveProng 2007-04-20, 9:25 pm |
| On 20 Apr 2007 18:02:53 -0700, conrad <conrad@lawyer.com> Gave us:
> And at the node
>where the branching takes place, current can
>flow down one branch(where a resistor exists)
>and it can flow down the second branch(where
>we have a short). Why does the majority of the
>current go down the path where we have a short?
Because. Ohm's law, dufus. Kirchoff's law as well.
| |
| MassiveProng 2007-04-20, 9:25 pm |
| On 20 Apr 2007 18:02:53 -0700, conrad <conrad@lawyer.com> Gave us:
>Even when
>measurements are taken, it can be observed that
>the majority of current goes down the least resistive
>path.
No... REALLY?
| |
| Ben Miller 2007-04-20, 9:25 pm |
| "conrad" <conrad@lawyer.com> wrote in message
news:1177117373.550034.231180@p77g2000hsh.googlegroups.com...
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
>
> --
> conrad
>
The "path of least resistance" is an inaccurate but very popular statement.
Current flows through ALL available paths, in an amount inversely
proportional to the resistance in each path.
By Ohm's law, the current through any part of the circuit is determined by
the potential difference across it divided by the resistance. Both parallel
branches have the same potential across them. Therefore, most of the current
would flow through the short, which has a very low but measurable
resistance. Less current would flow through the resistor.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
| |
| Don Kelly 2007-04-21, 3:25 am |
| "Ben Miller" <benmiller@worldnet.att.net> wrote in message
news:xpudnepq9e6-8LTbnZ2dnUVZ_ternZ2d@comcast.com...
> "conrad" <conrad@lawyer.com> wrote in message
> news:1177117373.550034.231180@p77g2000hsh.googlegroups.com...
>
> The "path of least resistance" is an inaccurate but very popular
> statement. Current flows through ALL available paths, in an amount
> inversely proportional to the resistance in each path.
>
> By Ohm's law, the current through any part of the circuit is determined by
> the potential difference across it divided by the resistance. Both
> parallel branches have the same potential across them. Therefore, most of
> the current would flow through the short, which has a very low but
> measurable resistance. Less current would flow through the resistor.
>
> Ben Miller
>
> --
> Benjamin D. Miller, PE
> B. MILLER ENGINEERING
> www.bmillerengineering.com
I think that the conceptual problems that many have is a focus on the
individual electron which, for a variety of reasons, doesn't matter a damn
when one steps up to the macroscopic world of circuit theory. Somewhere
common sense and observation of what actually goes on is ignored.
I really wonder how, when I turn on a light, that I get light right now
instead of when the electrons from the generator get to my home, several
hundred miles away, particularly for AC where they simply dither around and
don't get anywhere  --
Don Kelly dhky@shawcross.ca
remove the X to answer
----------------------------
| |
|
|
| nonsense@unsettled.com 2007-04-21, 9:25 am |
| conrad wrote:
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
You asked this question is both a science and an engineering
forum. Why is not a science question.
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
From an engineering/technician viewpoint you can use the
water pipe model to understand that more electrons will
fit into the larger "pipe."
Imagine a queue of people coming up to a branching of
the queue, with one branch being larger than the other.
Those in the queue who have no intent to select one branch
or the other are merely swept along. It is obvious that
more of them end up in the physically wider branch with
no forecasting required.
This could make a very nice trolling question.
| |
| Long Ranger 2007-04-21, 1:25 pm |
|
"conrad" <conrad@lawyer.com> wrote in message
news:1177117373.550034.231180@p77g2000hsh.googlegroups.com...
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
>
> --
> conrad
>
Think of the old hydraulic analogy: Imagine a pump putting a given pressure
into a manifold with an 1/8" outlet, and and a 4" outlet. If the pressure
remains static, which outlet will account for more flow? Same idea with
electrons. (Electrons, incidently, don't travel at "nearly the speed of
light". The electron pulse from one end of the circuit to the other, does.)
| |
| phil-news-nospam@ipal.net 2007-04-21, 1:25 pm |
| In alt.engineering.electrical conrad <conrad@lawyer.com> wrote:
| What happens at the atomic level
| where electrons have an affinity for
| a path of least resistance? Imagine this,
| you have a parallel circuit. And at the node
| where the branching takes place, current can
| flow down one branch(where a resistor exists)
| and it can flow down the second branch(where
| we have a short). Why does the majority of the
| current go down the path where we have a short?
| It isn't like electrons can forecast which path has
| least resistence, right? So how does the principle
| 'follows path of least resistence' hold? Even when
| measurements are taken, it can be observed that
| the majority of current goes down the least resistive
| path. It just doesn't make much sense when you
| know electrons cannot forecast whether a resistor
| or short lies ahead down one of the branches.
The resistance in the wiring (even if it's not much, as copper would be),
is kind of like a self generated bucking force that is proportional to
the current that is flowing. There is a voltage drop across any segment
of wire, and you'll see a voltage that obeys ohms law relative to the
current and the resistance.
The path with less reistance will have less of this bucking force. The
eletrical force is really trying to go in all paths at the same time.
Some paths just don't push back as much.
At the atomic level, I presume the electrons are encountering various
atomic level actions that prevent their most efficient flow, such as the
need to be changing electron orbital levels. The counter reactions could
be thought of as that bucking force.
The electrons cannot forecast which path has least resistance. When the
force (voltage) changes, that's when it can become apparent what is going
on. Suppose you have two very long paths of low resistance, interrupted
by one point of high resistance (e.g. a resistor inserted in the wire).
In one case the resistor is near the voltage source. In the other case
the resistor is nearer the other end (which might be a microsecond away
at near light speed). So what is the electricity doing before it has any
opportunity to "know" the circuit resistance (e.g. in the microsecond
before the leading edge of turned on voltage reaches the far resistor)?
The answer to that is characteristic impedance as seen in transmission
lines. You could, in theory, make 300 ohm twin lead TV wire out of
superconductors that offer no resistance at all (for our convenience in
calculation). There's a resistor at the far end (but it's not 300 ohms).
Or there may be nothing connected (open circuit). Or it may be shorted.
Or the resistor might actually be 300 ohms. But the electricity that
starts to flow can't "know" this for at least a microsecond of time.
What that electricity will do is behave on its leading edge based on
the characteristic impedance of the transmission line, which comes from
the inductance and capacitance of the line itself (real wire will also
add some resistance to that). When the leading edge reaches the far end,
what happens next depends on what is there. If shorted, the leading edge
will return on the other wire (there are 2 wires in the transmission line).
If open, it comes back on the same wire. If 300 ohms is there, it is all
dissipated and nothing comes back as a leading egde (a steady current will
flow). Other resistances will have a lesser effect than shorted or open.
That returning edge can end up reflecting back and forth between both ends
until it reaches a steady state (assuming you switched on DC power). If
you supply AC (changing voltage) these effects just keep on happening.
Radio engineers and ham operators have to deal with this on even very
short transmission lines (from transmitter to antenna) because at radio
frequencies, the voltage is changing up and down in less time that it
takes for the leading edge to reach the antenna. That can get very
convoluted (simplified forms of it get plotted on "Smith Charts"). But
it is fun to study.
In summary, electrons cannot "see" ahead. In fact they don't really even
flow literally very fast or far ("electron drift"). But the "bump effect"
itself moves at near light speed and comes back at near light speed and
that has counter effects that "report the distant resistance" via how much
has come back and when.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-04-21-1101@ipal.net |
|------------------------------------/-------------------------------------|
| |
| phil-news-nospam@ipal.net 2007-04-21, 1:25 pm |
| In alt.engineering.electrical Don Kelly <dhky@shaw.ca> wrote:
| I think that the conceptual problems that many have is a focus on the
| individual electron which, for a variety of reasons, doesn't matter a damn
| when one steps up to the macroscopic world of circuit theory. Somewhere
| common sense and observation of what actually goes on is ignored.
Sometimes I think the electrons are just along for the ride. The real
work is the EMF itself. If there is a cause-effect relationship (as
opposed to just a mutual coexistance), then it must be EMF as the cause
and electron flow as the effect.
| I really wonder how, when I turn on a light, that I get light right now
| instead of when the electrons from the generator get to my home, several
| hundred miles away, particularly for AC where they simply dither around and
| don't get anywhere --
And even if they could get very far, you don't get the same electrons (if
there could even be a concept of sameness between electrons) because they
would not cross the boundary of transformers. If you put a battery and an
appropriate resistance in series with the AC outlet, you could eventually
have some of the electrons from the transformer actually in your home. But
it wouldn't be the ones from the generating plants on the grid.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-04-21-1123@ipal.net |
|------------------------------------/-------------------------------------|
| |
| Palindrome 2007-04-21, 1:25 pm |
| phil-news-nospam@ipal.net wrote:
> In alt.engineering.electrical conrad <conrad@lawyer.com> wrote:
>
> | What happens at the atomic level
> | where electrons have an affinity for
> | a path of least resistance? Imagine this,
> | you have a parallel circuit. And at the node
> | where the branching takes place, current can
> | flow down one branch(where a resistor exists)
> | and it can flow down the second branch(where
> | we have a short). Why does the majority of the
> | current go down the path where we have a short?
> | It isn't like electrons can forecast which path has
> | least resistence, right? So how does the principle
> | 'follows path of least resistence' hold? Even when
> | measurements are taken, it can be observed that
> | the majority of current goes down the least resistive
> | path. It just doesn't make much sense when you
> | know electrons cannot forecast whether a resistor
> | or short lies ahead down one of the branches.
>
> The resistance in the wiring (even if it's not much, as copper would be),
> is kind of like a self generated bucking force that is proportional to
> the current that is flowing. There is a voltage drop across any segment
> of wire, and you'll see a voltage that obeys ohms law relative to the
> current and the resistance.
>
> The path with less reistance will have less of this bucking force. The
> eletrical force is really trying to go in all paths at the same time.
> Some paths just don't push back as much.
>
> At the atomic level, I presume the electrons are encountering various
> atomic level actions that prevent their most efficient flow, such as the
> need to be changing electron orbital levels. The counter reactions could
> be thought of as that bucking force.
>
> The electrons cannot forecast which path has least resistance. When the
> force (voltage) changes, that's when it can become apparent what is going
> on. Suppose you have two very long paths of low resistance, interrupted
> by one point of high resistance (e.g. a resistor inserted in the wire).
> In one case the resistor is near the voltage source. In the other case
> the resistor is nearer the other end (which might be a microsecond away
> at near light speed). So what is the electricity doing before it has any
> opportunity to "know" the circuit resistance (e.g. in the microsecond
> before the leading edge of turned on voltage reaches the far resistor)?
> The answer to that is characteristic impedance as seen in transmission
> lines. You could, in theory, make 300 ohm twin lead TV wire out of
> superconductors that offer no resistance at all (for our convenience in
> calculation). There's a resistor at the far end (but it's not 300 ohms).
> Or there may be nothing connected (open circuit). Or it may be shorted.
> Or the resistor might actually be 300 ohms. But the electricity that
> starts to flow can't "know" this for at least a microsecond of time.
> What that electricity will do is behave on its leading edge based on
> the characteristic impedance of the transmission line, which comes from
> the inductance and capacitance of the line itself (real wire will also
> add some resistance to that). When the leading edge reaches the far end,
> what happens next depends on what is there. If shorted, the leading edge
> will return on the other wire (there are 2 wires in the transmission line).
> If open, it comes back on the same wire. If 300 ohms is there, it is all
> dissipated and nothing comes back as a leading egde (a steady current will
> flow). Other resistances will have a lesser effect than shorted or open.
> That returning edge can end up reflecting back and forth between both ends
> until it reaches a steady state (assuming you switched on DC power). If
> you supply AC (changing voltage) these effects just keep on happening.
> Radio engineers and ham operators have to deal with this on even very
> short transmission lines (from transmitter to antenna) because at radio
> frequencies, the voltage is changing up and down in less time that it
> takes for the leading edge to reach the antenna. That can get very
> convoluted (simplified forms of it get plotted on "Smith Charts"). But
> it is fun to study.
>
> In summary, electrons cannot "see" ahead. In fact they don't really even
> flow literally very fast or far ("electron drift"). But the "bump effect"
> itself moves at near light speed and comes back at near light speed and
> that has counter effects that "report the distant resistance" via how much
> has come back and when.
>
And there was me thinking that the path of least resistance was between
a romantic candlelit meal for two and the bedroom ;)
--
Sue
| |
| phil-news-nospam@ipal.net 2007-04-21, 1:25 pm |
| In alt.engineering.electrical nonsense@unsettled.com <nonsense@unsettled.com> wrote:
| From an engineering/technician viewpoint you can use the
| water pipe model to understand that more electrons will
| fit into the larger "pipe."
Water pipe models are bad for electrical analogies. What would have to
change to make them more correct is that we would use water pipes as a
means to transport energy in the form of forward and reverse pressure
changes (or forward only if Mr. Edison had his way) ... instead of using
them as a means to acquire water.
The interesting thing in such a water based energy system is that the
very same water molecules might well never go beyond a few centimeters
of some point along the pipe in years, if the "AC" method is used.
Of course there is a general spreading around of molecules always taking
place (frozen is just a lot slower), so eventually some get into all
kinds of places. But electrons do that, too.
With such systems, it's actually possible to have analogies to components
like resistors, capacitors, inductors, and even transformers.
| Imagine a queue of people coming up to a branching of
| the queue, with one branch being larger than the other.
| Those in the queue who have no intent to select one branch
| or the other are merely swept along. It is obvious that
| more of them end up in the physically wider branch with
| no forecasting required.
Normally they would choose the better queue. But given no knowledge, such
as being blindfolded and following the crowd, this makes for a reasonable
analogy.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-04-21-1129@ipal.net |
|------------------------------------/-------------------------------------|
| |
| Salmon Egg 2007-04-21, 5:25 pm |
| On 4/20/07 6:02 PM, in article
1177117373.550034.231180@p77g2000hsh.googlegroups.com, "conrad"
<conrad@lawyer.com> wrote:
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
>
> --
> conrad
>
You are barking up the wrong tree. At the atomic level, there is no
resistance in the classical sense. Electrons have something like wave
behavior. The waves can travel over ALL possible paths. The net wave result
comes from paths near the classical path. The net result is that the wave
intensity provides the relative PROBABILITY where an electron will be found.
A resistor is large compared to atomic spacings. Electrons accelerate in the
conductor until they collide with something and on the average lose their
velocity.
If you are truly interested, Google Feynman and "path integral."
Bill
-- Fermez le Bush--about two years to go.
| |
| phil-news-nospam@ipal.net 2007-04-21, 8:25 pm |
| In alt.engineering.electrical MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote:
| On 20 Apr 2007 18:02:53 -0700, conrad <conrad@lawyer.com> Gave us:
|
|>Even when
|>measurements are taken, it can be observed that
|>the majority of current goes down the least resistive
|>path.
|
| No... REALLY?
Not!
If you have a path with 26 ohms, and a 2nd path with 25 ohms, and a 3rd
path with 24 ohms, you won't find the majority of current in any one of
them.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-04-21-1932@ipal.net |
|------------------------------------/-------------------------------------|
| |
| Don Kelly 2007-04-21, 9:25 pm |
| ----------------------------
"Timo A. Nieminen" <timo@physics.uq.edu.au> wrote in message
news:Pine.WNT.4.64.0704211647020.1188@serene.st...
> On Sat, 21 Apr 2007, Don Kelly wrote:
>
>
> The electrons are just incidental; the wires are a waveguide. Stratton's
> book covers it well.
>
> --
> Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
> E-prints: http://eprint.uq.edu.au/view/person...n,_Timo_A..html
> Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
Agreed: even though I prefer to stick to low frequency stuff -say 5000km
wavelength - where simple circuit theory and, at most, distributed parameter
T-line concepts, are more than adequate approximations to waveguide
concepts.
Note the "Smiley">
--
Don Kelly dhky@shawcross.ca
remove the X to answer
>
| |
| Timo A. Nieminen 2007-04-22, 3:25 am |
| On Sun, 22 Apr 2007, Don Kelly wrote:
> "Timo A. Nieminen" <timo@physics.uq.edu.au> wrote:
>
> Agreed: even though I prefer to stick to low frequency stuff -say 5000km
> wavelength - where simple circuit theory and, at most, distributed parameter
> T-line concepts, are more than adequate approximations to waveguide
> concepts.
Circuit theory is a perfectly good low frequency method. Doing stuff in
the gap between circuit theory and geometric optics is enough to make one
appreciate the value of low/high frequency approximations.
> Note the "Smiley">
Given your usual posts, a smiley is hardly necessary . But I thought
the casual reader might be interested.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person...n,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
| |
| Long Ranger 2007-04-22, 8:25 pm |
|
<phil-news-nospam@ipal.net> wrote in message
news:f0deir2hul@news1.newsguy.com...
> In alt.engineering.electrical nonsense@unsettled.com
> <nonsense@unsettled.com> wrote:
>
> | From an engineering/technician viewpoint you can use the
> | water pipe model to understand that more electrons will
> | fit into the larger "pipe."
>
> Water pipe models are bad for electrical analogies. What would have to
> change to make them more correct is that we would use water pipes as a
> means to transport energy in the form of forward and reverse pressure
> changes (or forward only if Mr. Edison had his way) ... instead of using
> them as a means to acquire water.
A hydraulic analogy is pretty useful in explaining electric phenomena to lay
people. It is analogous to DC when compared to a hydraulic pump running a
hydraulic motor, and even to AC when you consider the current at it's RMS
value in many applications. Obviously, transformer theory and rotating
fields don't apply here, but even then, the total of energy etc is still
analogous to pumping.
| |
| Ben Miller 2007-04-23, 3:25 am |
| <phil-news-nospam@ipal.net> wrote in message
news:f0deir2hul@news1.newsguy.com...
> Water pipe models are bad for electrical analogies. What would have to
> change to make them more correct is that we would use water pipes as a
> means to transport energy in the form of forward and reverse pressure
> changes (or forward only if Mr. Edison had his way) ... instead of using
> them as a means to acquire water.
I disagree. You may be right at an engineering level, but try to explain
electrical basics to a group of non-electrical industrial workers. They
understand the relationship between pressure, water flow, and valve
restriction. They work with it every day at their sinks and showers. The
electrical analogy allows them to correctly understand the relationship of
voltage, current, and resistance.
I can assure you from experience that it works!
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
-------------------------------------|
| |
| SuperM 2007-04-23, 3:25 am |
| On Sun, 22 Apr 2007 22:20:03 -0500, "Ben Miller"
<benmiller@worldnet.att.net> Gave us:
><phil-news-nospam@ipal.net> wrote in message
>news:f0deir2hul@news1.newsguy.com...
>
>I disagree. You may be right at an engineering level, but try to explain
>electrical basics to a group of non-electrical industrial workers. They
>understand the relationship between pressure, water flow, and valve
>restriction. They work with it every day at their sinks and showers. The
>electrical analogy allows them to correctly understand the relationship of
>voltage, current, and resistance.
>
>I can assure you from experience that it works!
Absolutely true.
| |
|
|
Salmon Egg wrote:
> You are barking up the wrong tree. At the atomic level, there is no
> resistance in the classical sense. Electrons have something like wave
> behavior. The waves can travel over ALL possible paths. The net wave result
> comes from paths near the classical path. The net result is that the wave
> intensity provides the relative PROBABILITY where an electron will be found.
>
> A resistor is large compared to atomic spacings. Electrons accelerate in the
> conductor until they collide with something and on the average lose their
> velocity.
>
> If you are truly interested, Google Feynman and "path integral."
And you probably thought my answer early in this thread was just me
being a wise-XXX! Well, yeah, I was, but the question really is a
serious and a mysterious one at the microscopic level. Answers at the
circuit level are really just approximations to truth. The point is
just HOW do electrons "look ahead" and see what's going on? In the
case of a load and a short, they actually don't! Consider a wire that
splits into a Y where one path is a short and the other is a resistor.
You can ask how does the electron "know" that one path is shorted so
more of them go that way? Fact is it doesn't work that way. If you
put a sharp step into your Y wire, you'll have a wave-pulse that
travels down the outside of the wire. That impulse travels usually
somewhere near the speed of light and as it goes down the "stem" of
the Y it really has no idea that there is a "short" ahead. It can't
know anything in the "cone of silence" which is to say in regions that
require speeds faster than light for communication. So therefore this
energy (which actually is in the field around the wire and not in the
electrons) doesn't in fact "know" what lies ahead. It is only after
this pulse explores both branches and bounces around a bit that
finally circuit equations begin to apply. Circuit theory is handy for
quick answers but field theory or even quantum theory is needed to get
at microscopic truth.
But what if we take "free" electrons hurtling through empty space. We
find that if we set up two slits, each electron actually only goes
through one slit at a time. Yet, SOMEHOW it also "knows" that the
other slit is there because on average with lots of flying electrons
the landing patterns formed will be a two slit diffraction pattern.
OK, so just HOW does a single electron going through ONE hole "know"
that the other hole is just over there? Good Question! Physicists do a
lot of hand waving and jibber-jabbering about probability waves and
the like, but it's all very imaginary and quite unsatisfying! [Go see
Feynman] Does God play dice with the Universe? The world is waiting
for an explanation for this that doesn't require a priesthood in Wicca
to understand.
Benj
(Who notes that it's a poor student who can't ask a simple question
that stumps the world)
| |
| SuperM 2007-04-23, 9:25 am |
| On Sat, 21 Apr 2007 21:36:06 GMT, Salmon Egg <salmonegg@sbcglobal.net>
Gave us:
>A resistor is large compared to atomic spacings. Electrons accelerate in the
>conductor until they collide with something and on the average lose their
>velocity.
Which is also why the resistor heats up when current is driven
through it. This is what defines a semi-conductor. Such collisions
are exactly how a resistor works. Driving electrons from valence
shells with EMF to produce flow.
| |
| SuperM 2007-04-23, 9:25 am |
| On 22 Apr 2007 22:44:34 -0700, Benj <bjacoby@iwaynet.net> Gave us:
>The point is
>just HOW do electrons "look ahead" and see what's going on?
That is a dopey question and proves that you don't have a grasp of
the circumstances under which a circuit operates.
It is a complete loop. You need to start over with your basic
electronics training.
I suggest the NEETs program.
http://www.tpub.com/content/neets/index.htm
| |
| SuperM 2007-04-23, 9:25 am |
| On 22 Apr 2007 22:44:34 -0700, Benj <bjacoby@iwaynet.net> Gave us:
>That impulse travels usually
>somewhere near the speed of light and as it goes down the "stem" of
>the Y it really has no idea that there is a "short" ahead.
You're nuts.
| |
|
|
SuperM wrote:
> On 22 Apr 2007 22:44:34 -0700, Benj <bjacoby@iwaynet.net> Gave us:
>
>
>
> You're nuts.
Hey there, SuperM, you really need to keep your mouth shut until you
complete your basic electronics training... or at least wait until you
get to the chapter labeled "transmission lines".
Benj
(who notes it better to keep your mouth shut and be thought a fool
than to open it and remove all doubt)
| |
| Don Kelly 2007-04-23, 9:25 pm |
| ----------------------------
"Benj" <bjacoby@iwaynet.net> wrote in message
news:1177307073.980428.79890@b75g2000hsg.googlegroups.com...
>
> Salmon Egg wrote:
>
> And you probably thought my answer early in this thread was just me
> being a wise-XXX! Well, yeah, I was, but the question really is a
> serious and a mysterious one at the microscopic level. Answers at the
> circuit level are really just approximations to truth. The point is
> just HOW do electrons "look ahead" and see what's going on? In the
> case of a load and a short, they actually don't! Consider a wire that
> splits into a Y where one path is a short and the other is a resistor.
> You can ask how does the electron "know" that one path is shorted so
> more of them go that way? Fact is it doesn't work that way. If you
> put a sharp step into your Y wire, you'll have a wave-pulse that
> travels down the outside of the wire. That impulse travels usually
> somewhere near the speed of light and as it goes down the "stem" of
> the Y it really has no idea that there is a "short" ahead. It can't
> know anything in the "cone of silence" which is to say in regions that
> require speeds faster than light for communication. So therefore this
> energy (which actually is in the field around the wire and not in the
> electrons) doesn't in fact "know" what lies ahead. It is only after
> this pulse explores both branches and bounces around a bit that
> finally circuit equations begin to apply. Circuit theory is handy for
> quick answers but field theory or even quantum theory is needed to get
> at microscopic truth.
>
> But what if we take "free" electrons hurtling through empty space. We
> find that if we set up two slits, each electron actually only goes
> through one slit at a time. Yet, SOMEHOW it also "knows" that the
> other slit is there because on average with lots of flying electrons
> the landing patterns formed will be a two slit diffraction pattern.
> OK, so just HOW does a single electron going through ONE hole "know"
> that the other hole is just over there? Good Question! Physicists do a
> lot of hand waving and jibber-jabbering about probability waves and
> the like, but it's all very imaginary and quite unsatisfying! [Go see
> Feynman] Does God play dice with the Universe? The world is waiting
> for an explanation for this that doesn't require a priesthood in Wicca
> to understand.
>
> Benj
> (Who notes that it's a poor student who can't ask a simple question
> that stumps the world)
---------------
I hope that no one is saying that circuit equations apply to a single
electron or even to the travelling wave.
Circuit theory is a first order approximation to field theory and is valid
only at the macroscopic level and when non-relativistic effects occur.
Salmon Egg is correct in pointing out the probabilistic nature of what goes
on at the microscopic level.
Even at the macroscopic level, the model for a particular element-say a
piece of wire can consist of a) a short circuit
b)a lumped resistance
c)lumped resistance and inductance
d) lumped R,L,C
e)transmission line
d) EM models
etc.
depending on frequency.
a-e are approximations to d. One could use d for everything but the
approximations are more than adequate within bounds. A big factor is knowing
what the bounds are because one doesn't use EM to deal with a DC
battery-wire-lamp problem.
So -is the cat alive or dead?
--
Don Kelly dhky@shawcross.ca
remove the X to answer
>
| |
| SuperM 2007-04-24, 3:25 am |
| On 23 Apr 2007 07:49:12 -0700, Benj <bjacoby@iwaynet.net> Gave us:
>
>Hey there, SuperM, you really need to keep your mouth shut until you
>complete your basic electronics training... or at least wait until you
>get to the chapter labeled "transmission lines".
Your "dead short scenario, AND you assessment of what happens is
what proves you are lost.
>
>Benj
>(who notes it better to keep your mouth shut and be thought a fool
>than to open it and remove all doubt)
Too late for you then.
| |
| Paul Hovnanian P.E. 2007-04-24, 3:25 am |
| conrad wrote:
>
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance?
It doesn't really. It divides among all paths such that the current
through each path and that path's impedance satisfy the requirement that
nodes common to multiple paths have one defined voltage.
> Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
Because an amount of current must flow down each branch such that the
voltage across each branch (between two common nodes) is the same.
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
It can't. From an electron's point of view as it approaches a branch,
its probability of taking one or the other depends on the potential
gradient it 'sees' ahead of it (like charges repel). Along a path of
lower resistivity, it takes a higher current density to produce a given
gradient. So that electron doesn't have to 'see' all the way down one
path. The electrons ahead of it have taken care of that already.
Its sort of like how a traffic jam works. You slow down if there's a
wreck miles ahead.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Why are so many towns named after water towers?
| |
| Salmon Egg 2007-04-24, 3:25 am |
| On 4/23/07 3:58 AM, in article e44p23l9eas6csgp6nag28jprs21tc3akl@4ax.com,
"SuperM" <SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org> wrote:
> Which is also why the resistor heats up when current is driven
> through it. This is what defines a semi-conductor. Such collisions
> are exactly how a resistor works. Driving electrons from valence
> shells with EMF to produce flow.
It is a bit more complicated than that. Electrons (or holes or even ions in
electrolytes) will collide with impurities and lattice imperfections
(dislocations). That is why copper for wire is pure and annealed. That is
why nichrome is good for resistors. Electrons will even scatter off of
lattice vibrations (phonons). That is why resistance of good metallic
conductors increases with temperature.
Bill
-- Fermez le Bush--about two years to go.
| |
| Chugga Chug 2007-04-24, 9:25 am |
| > What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
Electrons follow the path of best attraction, which just happens to be the
path of least resistance, or most persistence. Resistance resists
attraction.
You are very persistant ;-)
| |
| do.not@reply.nonet 2007-04-24, 9:25 am |
| According to a presentation I saw yesterday you start
with Schrödinger's equation, fill in the unknowns, which
for each electron is about 20 and it all essentially
reduces to Newton's second law (f=ma), then you just
let a computer simulate it all. Several hundred hours
of computing later and your electrons will have convected,
through the varying electric fields, past a few of the few
hundred atoms in your finite simulation. Hopefully you
will have done enough to spot the trend in the directions
that the electrons are going.
I suggest the electrons don't know anything about any
paths of resistance, they are only influenced by the local
(to them) electric field. The models of materials usually
have the electrons moving about pretty fast, but not consistently
in the same direction because the electric field gradients they are
seeing are huge, but over very small (interatomic) distances.
Current is an average of all the movements and circuit theory
applies to the averages of the quantities in time and space.
Perhaps an interest discussion would be "what is it, on an
interatomic scale, the features that gives different materials
different electrical resistance?"
The presentation I saw was actually about crack propagation,
but essentially the same sort of stuff.
Well done Conrad, for stimulating the brain cells in the
branches the thoughts only go through rarely.
Robert
conrad wrote:
> What happens at the atomic level
> where electrons have an affinity for
> a path of least resistance? Imagine this,
> you have a parallel circuit. And at the node
> where the branching takes place, current can
> flow down one branch(where a resistor exists)
> and it can flow down the second branch(where
> we have a short). Why does the majority of the
> current go down the path where we have a short?
> It isn't like electrons can forecast which path has
> least resistence, right? So how does the principle
> 'follows path of least resistence' hold? Even when
> measurements are taken, it can be observed that
> the majority of current goes down the least resistive
> path. It just doesn't make much sense when you
> know electrons cannot forecast whether a resistor
> or short lies ahead down one of the branches.
>
> --
> conrad
>
| |
| phil-news-nospam@ipal.net 2007-04-28, 3:25 am |
| In alt.engineering.electrical Palindrome <me9@privacy.net> wrote:
|> In summary, electrons cannot "see" ahead. In fact they don't really even
|> flow literally very fast or far ("electron drift"). But the "bump effect"
|> itself moves at near light speed and comes back at near light speed and
|> that has counter effects that "report the distant resistance" via how much
|> has come back and when.
|>
|
| And there was me thinking that the path of least resistance was between
| a romantic candlelit meal for two and the bedroom ;)
Believe me ... some never make it to the bedroom!
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-04-27-2151@ipal.net |
|------------------------------------/-------------------------------------|
|
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