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Author Topic: A question about resistance  (Read 4557 times)

spiralout

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A question about resistance
« on: April 17, 2009, 01:49:49 PM »
Hi folks,

I'm no expert and I have no degree,
But I'm a curious little bastard,
With the patience of a tree,

I was pondering the matter of resistance,
Then a thought appeared one instance,
While I gazed upon the forest from a distance,

I was struggling to phrase it as it came,
They are illusive, hard to tame,
It might be childish but I'll ask it all the same.  :)

So, from the little that I know, resistance of any given wire,
is determined  by the material it is composed of and by it's diameter,
is that correct so far?

What would happen if  we create a wire that is non linear?

What I'm getting at is that the resistance of the wire
will remain constant as long as the wire retains the same diameter, right?
So, what happens to the resistance and the behavior of the current all together,
if  we have a wire that starts out very thin and gradually becomes thicker? 
For example, a 2 meter long copper wire that is 0.1mm at the beginning
and widens slowly to 3mm at the other end.

What would happen if electricity flows from thin to thick and vice verse?

I'll appreciate any thoughts and explanations,
But PLEASE, spare me from you're verbal violence,
And any other condemnations.

Thanks a lot,

Adam.

Doug1

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Re: A question about resistance
« Reply #1 on: April 17, 2009, 02:15:40 PM »
You can work that test out yourself using extension cords to a power tool like a circular saw.

jibbguy

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Re: A question about resistance
« Reply #2 on: April 17, 2009, 02:46:52 PM »
To R it would not matter,
That the wire were fatter....
It is not a tapered lead
That determines current feed...

Each Ohm could be an infinite set
.. Of small R's in series? You bet.

The circuit branch's total "R"
must be the deciding bar.

Z mixes in C and L too..
For this is the other shoe.
But the result's the same
when a resistor is the game.

The "water" current that flows
Is not set by the "river's" width
Nor by the banks' highs and lows.
It is set at the mouth to the sea,
and by little boys fishing who pee.

Paul-R

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Re: A question about resistance
« Reply #3 on: April 17, 2009, 04:49:20 PM »
...and of course, the material affects the resistance. Silver best, copper good.
Also, the skin carries the bulk of the current.

Someone once asked how current could be brought to a halt half way down the
wire. If I rememeber right, he brought that thread to a halt. But there is something
interesting in these musings. I'm not sure exactly what.

spiralout

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Re: A question about resistance
« Reply #4 on: April 17, 2009, 06:15:46 PM »

@ jib,

Do you mean there would be no effect what so ever?

Somehow it defies my inner logic. this question
came to my mind as I was thinking about fractals
and how everything in the natural world is pretty
much the same, no matter what scale you look at.
inverse scaling is the correct term, i believe.

Actually, I think I might have looked at it from the
wrong direction. I'm much more curios to know how
will the conductivity of this kind of wire would behave.
I'm thinking graphically here, but would it not focus
or disperse the current, depending where the power is coming from?

Thanks for your time,

Adam


 







jibbguy

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Re: A question about resistance
« Reply #5 on: April 17, 2009, 10:10:10 PM »
Adam,

Yer welcome. 

There could certainly be differing effects if AC frequency is involved (or single-polarity-going pulses of varying F), especially if Capacitance and/or Induction were factors in the circuit too (that is the "Z" Impedance factor, and includes Phase, and is highly dependent on Frequency and even waveform shape). But in "straight" (DC) Resistance.. "Nope", no difference could be detected in R between materials or sizes with the same Ohm rating (other than that caused by over-heating if the conductor / resistor were too small for the current load).

What you might see though, is significant differences in magnetic field strength between different conductors (for instance, a thick flat bar verses a twisted pair of wires but both having the same DC Ohm value.. The bar could create a fairly large magnetic field where the twisted wires would have hardly any). This magnetic field generated by current passing through the conductor could possibly affect other nearby components, and give the illusion of a different DC Resistance or otherwise cause "problems".

I remember this happening once with a current shunt (metal bar with like 0.3 Ohm R, used to read the V across it to calculate current); it gave off a magnetic field when at higher current loads that messed with a nearby little choke coil and thereby increased "loose capacitance" that in turn stopped an LM gate in an entirely different logic branch of the circuit from working reliably, lol. These kinda things are the main reason you see so many "Revisions" listed on schematics (well, next to not being able to source a certain component any more which is the top reason). 

And "Conductance" is a different story than "Resistance", since there are differing qualities for every material and grade and it is also frequency-dependent with some materials.  Also, very low ambient temperatures could have an effect on different materials' R rating. But in the end, there should always be a definite and repeatable "Ohms" value for the DC Resistance of the material at any one set point in time. Lol, and be glad for this as it is about the only Constant that we can rely on ;)

nitinnun

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Re: A question about resistance
« Reply #6 on: April 17, 2009, 10:58:23 PM »
don't use copper wire.

wire is an imperfect implementation compromise,
from the 1800's.

Tesla must only have used it,
because at the time,
they lacked the machining quality to do better.


use a long,
wide,
flat strip of copper foil.

such as copper fletching,
from the hardware store.
even if you have to cut it into smaller strips.


solder the copper foils sharp edges,
with a thin layer of soldering material.
to "smooth" the edges.

this should prevent corona discharge,
of the amperage.


then cover the copper foil,
with the insulation of your choice.
such as sandwiching it between 2 slabs of cardboard,
which are taped and/or zip tied together.

or use 2 or 3 layers of trash bag,
if you need flexible insulation

(some people use trash bag,
to make super capacitors,
for their Tesla Coils.
so be confident, that it works)


this "smooth edged copper foil",
would in theory have a superior current bandwidth,
on both its surfaces.
with the thin inner atoms,
being mostly unused anyway.


if you coiled several feet of smooth foil,
into a ring shaped coil,
it might create an interesting magnetic field.


of course copper wire,
still has its advantages.

(if you have the money and machining abilities,
to get it).

(or you don't mind 90% of the copper inside the wire,
wasting space,
wasting material,
and wasting money).


just as the smoothed edge foil,
has its advantages.

(it should be much tougher against physical damage.
being much harder to cause discontinuity in it,
through bending/abuse).

(ironically, i think the foil is cheaper,
than an equal amount of copper wire.
because the foil must be easier to smelt,
without critical imperfections,
than the wire).

« Last Edit: April 17, 2009, 11:21:13 PM by nitinnun »

spiralout

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Re: A question about resistance
« Reply #7 on: April 17, 2009, 11:32:32 PM »

@jib,

wow,  thanks a million for your time and effort
my current knowledge of the technical terms
doesn't allow me to understand all of it right now,
but I'll get there...  :)

@nitinnun,

Thanks man, some good stuff to chew on...


Adam




 


Philip Hardcastle

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Re: A question about resistance
« Reply #8 on: April 18, 2009, 02:34:59 AM »
It strikes me that if the wire be from fat to thin,
and the electrons doth flow towards the narrow.
Then there should be an electron gas pressure within
that upon the increase of diameter, as though left fallow,
would cause a drop in temperature, or is that shallow?

spiralout

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Re: A question about resistance
« Reply #9 on: April 18, 2009, 01:51:21 PM »

@Philip,

Not shallow but profound,
I really like the way it sounds.
For energy to move around,
Potential difference should be found,

Now the cone he is quit strange,
In the way that he's arranged,
In his design there is a seed,
Potential difference he might feed.

LOL, I'm on a role! ;D

@All

I just saw a movie which had a short
explanation about the dynamics of tornado
creation. Simply put, cold front encounters
hot front and the potential difference between
them creates an elongated cone of spinning
energy. Beautiful things to watch, tornadoes.

Anyway, that made me think, is there a way
to reverse the process? I'm talking small scales,
of course. Can we somehow imitate the phenomena?

These are some thoughts of the top of my head,
if it resonates with someone, please let me know
if there is some merit to it.


Cheers,

Adam
 


Philip Hardcastle

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Re: A question about resistance
« Reply #10 on: April 18, 2009, 05:06:31 PM »
Re tornadoes

If electrons within a metal are considered as a gas, then a temperature gradient causes turbulence.

voltages are produced in wires due to temperature as we all know.

What is overlooked is the fact that an electron carries heat as well as charge.

So if we create a vortex similar to a tornado then perhaps we can create an electrical generator in a shaped piece of metal fed by heat at the right points and with the exhaust at an apex, and maybe its efficiency could be quite high.

Now this does not rhyme at all, but does it ring a bell?

Mr.Entropy

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Re: A question about resistance
« Reply #11 on: April 18, 2009, 07:55:29 PM »
So, from the little that I know, resistance of any given wire,
is determined  by the material it is composed of and by it's diameter,
is that correct so far?
No.  The resistance of a wire is determined by the material, diameter, and length.  The resistance of a particular diameter of copper wire is given in ohms per foot.  You have to multiply by the number of feet to get resistance in ohms.

Quote
What would happen if  we create a wire that is non linear?
The resistances of each little section of wire, over which the diameter is pretty much constant, add up to the resistance of the whole wire.

spiralout

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Re: A question about resistance
« Reply #12 on: April 19, 2009, 09:13:23 AM »

@Philip,

I'm in no position to determine
if what you say holds water,
but it is quit intriguing, to say the least.

Is there a way to release the heat
from the electron instead of his charge?
Is that what happens in commonly found
heating bodies, like in a kettle? 

Maybe there's a way to use that heat
directly without electricity as the middle man?

@Mr.Entropy,

Thanks for the clarification about resistance.
As for the second part of your comment,
I think the image that I have in my head
is not getting through.

What I was thinking of is a wire that
has no sections, but rather a continuous
slope. In such a case the constant will
no longer be the diameter, it would be the
changing of the diameter.

I'm not even sure why I insist on this
point, but it feels like there's something
here that is eluding us.
What might happen if we take a wire
of this kind and make a coil out of it?


Thanks for your time,


Adam.

 



 





Philip Hardcastle

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Re: A question about resistance
« Reply #13 on: April 19, 2009, 09:54:30 AM »
@Adam,

glad you asked, pls see curled ballistic thermionics on this site (actually misspelt as "Curled Ballisitic")

Clearly heat (kinetic energy) of electrons does work in thermionics to escape the surface of a metal.

What excess energy (kinetic) it has can be used too.

I believe Thermionics is the purest form of free energy available.

Phil

spiralout

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Re: A question about resistance
« Reply #14 on: April 19, 2009, 02:27:58 PM »

@Phil,

Thanks for your input,

I read your thread and it's very interesting.
My background is in industrial design so I
couldn't escape the feeling of a child eavesdropping
on an adult conversation  :)
Nevertheless I was very impressed with your
attitude and passion, we can all use some of that.

As I already said, my knowledge of physics is
somewhat limited. That might seem like an obstacle
to some, but it leaves me free to fantasize and speculate
outside the restrictions and "laws" of convectional science.

One of the deepest insights I had, as to do with the
shape of things and how it affects the energy flow
in them. My biggest source of inspiration is nature
and the myriad of shapes that it manifests.
Natural shapes have one thing in common,
they are never static. They are always on the move,
without even moving. Ever expanding or ever contracting,
depending which way you look.
 
@all
 
Another question that bugs me is about the
piezoelectric phenomena. If I understand correctly,
the current produced by a piezo crystal, consists of high
voltage and very low Amps. So, my question is:
How come a huge voltage with low Amps can pass
through my body hardly noticed, while much lower
voltage with higher Amps will fry me? what is this
mysterious component we call Amps? and why does
it have such a nasty bite?

Thanks in advance for any comments,

Adam.