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CrimpJiggler
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[*] posted on 3-1-2012 at 17:28
Separating cations from anions


Heres something I've been pondering. Lets I have a solution containing electrolytes, in this case lets say an NaCl solution. Lets say I put the beaker in an electric field so that one side of the beaker is beside a positive terminal and the other side of the beaker is beside the negative terminal. Will the cations flow to the right side of the beaker, while the anions flow to the left side? The answer to this is probably yes, so what happens if I put a barrier right in the middle of the beaker then remove the electric field? Will the ions all get stuck to the barrier?
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AndersHoveland
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[*] posted on 3-1-2012 at 18:19


Essentially the answer is no. Unless much higher voltages are involved, there will not be much separation of ions. In typical electrolytic solutions, ions only continue to flow because they are neutralized at the same rate. In the case of passing electric current through salt water, chlorine gas and hydogen are given off. If the formation of chlorine and hydrogen were somehow prevented, the electric current would stop flowing through the solution. Charged ions would build up at either end, preventing the flow or more ions. As I previously mentioned, the charge that would build up is negligable at low voltages. But at around 30kV there would start to be a detectable static charge that could potentially build up.
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neptunium
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[*] posted on 4-1-2012 at 12:29


in a liquide (solution) the electrons from the electrodes constantly bang against the molecules of the liquide hence the average distance any electron can travel before hiting somethying is negligeable.
the same experience in a low pressure setting would give a much different result .Ions will build up (giving a voltage high enough to break the resistance of whatever material is under low pressure) and even give off lights (when capturing an electron and returning to a lower state of energy) .

even at 100kV the experience is not visually stimulating ...the flow of electron (amps) should also be raised significantly to even detect any built up charges and as soon as the currant stops all the charges would be lost to the surrounding air fairly rapidly separation or not.
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CrimpJiggler
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[*] posted on 4-1-2012 at 17:00


Sorry I shoulda clarified this in the OP, I'm not talking about a solution in which electrodes are submerged, I'm talking about a solution with two high voltage terminals on each side of the beaker so that there is a high voltage across the beaker but no current can flow (because there is no conductive path connecting the solution to the terminals of the power source). There should be an electrostatic interaction between the electrical field produced by the power source and the ions in the solution.

I'm having trouble explaining this so I'll just use examples: you know when you rub a piece of plastic wrapper again a carpet or something and then there is an invisible attraction between the plastic and your hand despite there being no connection between you and the plastic. In that example, the plastic has a slight positive charge and is attracted to the your more negatively charged hand. Now lets say I have a high voltage power source instead and I hook one end of a wire up to the positive terminal of the power source and the other end of the wire to a big metal plate. That big metal plate will now be highly positively charged. The plate will be so attracted to my hand that if my hand gets too close to it, it will pull electrons off my hand via a miniature lightning bold through the air. If I put a big sheet of glass (which is far less conductive than air) in between my hand and the metal plate then my hand can get near the plate without getting shocked. Now there is no way for electrons to travel between my hand and the metal plate but the plate will still exhibit an electrostatic force on my hand, won't it? You can see that in those plasma balls, when you put your hand up to the glass, the electricity beams go for your hand. What I'm wondering is what effect this type of electrostatic force has on electrolytes. Will the positively charged plate attract anions in the solution? I don't see why it wouldn't. It you get a second big metal plate and hook it up to the negative terminal of the power source them place it at the opposite side of the beaker, will it attract the cations in the solution? I know that cations would tend to drag anions with them and vice versa but extremely high voltages would overcome those interionic forces and cause the cations and anions to migrate to opposite sides of the beaker, wouldn't they? One idea for testing this idea that comes to mind is using a salt in which both the cation and anion are absorb visible light of different wavelengths. In other words, the cation is a different colour to the anion so for example, lets say the cation is red and the anion is blue. A solution of these ions would appear green or something but the voltage did indeed cause the ions to migrate to opposite sides of the beaker, a colour gradient would emerge. Anyone up for testing this out? I don't have a high voltage power supply and I don't have any coloured salts like this. The salt would have to some kind of conjugated acid ionically bonded to a conjugated base.

EDIT: In this scenario, it would have to be a DC power supply obviously.

[Edited on 5-1-2012 by CrimpJiggler]
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watson.fawkes
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[*] posted on 4-1-2012 at 18:18


Quote: Originally posted by CrimpJiggler  
There should be an electrostatic interaction between the electrical field produced by the power source and the ions in the solution.
Yes, there's ion migration. What you're describing is similar to how the electrolyte in an electrolytic capacitor works. If you were to suddenly separate the two plates of a charged capacitor, then yes, there would be an electrostatic force between the plates.
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neptunium
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[*] posted on 4-1-2012 at 18:29


ooooooooh i see...ok the reason why those plasma balls work when you rub your hand on them is because the gas inside is at low preassure , it wouldnt work in the air much less in a liquid.
and putting a solid in between would put the final nail in that coffin
much like we dont get zapped everytime we grab an extantion cord under power because the rubber between the copper wire and our hand isnt conductive , glass holding the solution would prevent the electrical field from reaching in. the field would be all arround the beaker....now it would be interesting to see what happen in space in a weightlessness situation? probably deform the liquid bubble to an oval shape untill it get too close to one of the plate and breaks the electrical resistance of the air and sparks start to fly...
if i understand what you explained correctly...
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AndersHoveland
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[*] posted on 4-1-2012 at 22:18


Quote: Originally posted by neptunium  
the reason why those plasma balls work when you rub your hand on them is because the gas inside is at low preassure , it wouldnt work in the air much less in a liquid.
and putting a solid in between would put the final nail in that coffin much like we dont get zapped everytime we grab an extantion cord under power because the rubber between the copper wire and our hand isnt conductive , glass holding the solution would prevent the electrical field from reaching in.


Not quite. The plasma balls which you refer to involve high frequency alternating current, which can effectively go through thin non-conductors because of the capacitance effect. Note that the current goes through, not any actual electrons. Electrical fields are different from electric current. Electric fields typically go through anything (with the exception of superconductors or faraday cages that cancel out the effects of the field).

Air does not become conductive unless the voltage is high enough to ionize it. This is not necessarily in the form of an arc, but can also be in the form of corona discharge, which looks like a faint purple glow, accompanied by a hissing sound, a discernable movement of air, and the smell of ozone. If the current is high enough, the corona discharge (which contains ions) will transform into an arc (which contains plasma). At this point, the air will suddenly become much more conductive.

[Edited on 5-1-2012 by AndersHoveland]
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neptunium
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[*] posted on 4-1-2012 at 22:25


I stand corrected!

i took one of these plasma ball apart ones to see what it was made of. It had a sticker on the insisde warning about high voltages so I used it as an electron source in a vacuum tube ,couldnt get more than about 15kV out of it though,
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Rosco Bodine
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[*] posted on 7-1-2012 at 02:12


@AndersHoveland, Once again you are making affirmative statements about matters where observation of what actually occurs does not square with what you are saying. There is most definitely an electric field present and/or real current flow through the medium of air for example that is present across the bare terminals of even a low voltage battery. This can most easily be illustrated by the behavior of a device called an IGFET (insulated gate field effect transistor) operating in enhancement mode, like an N-channel MOSFET. A simple circuit can be made using test leads with clips and a voltmeter and a battery and a MOSFET, where the battery, voltmeter, and MOSFET are connected in series through the Source and Drain leads of the MOSFET, with a test lead having one end clipped to the Gate lead of the MOSFET to serve as an antenna for receiving "signal" which
will traverse the air and modulate current through that voltmeter which will
show the level of current flowing. A supplemental pair of test leads have one end of each connected to the different polarity terminals of the battery, any battery is
fine such as 12 volts or less, a 9 volt transistor battery is fine for this experiment.
Grasp with one hand the free end of the test lead attached to the positive terminal of the battery, and with your other hand point your finger at the free end of the test lead serving as the "antenna" attached to the Gate lead of the
MOSFET, and observe the voltmeter registering the amplified response of the
MOSFET as you move your fingertip nearer to the bare end of the "Antenna" lead,
or pull back your fingertip further away. Let us know what are your conclusions
from such an experiment ......is the effect purely "field effect" or is there actual
current flow through the air by electrons. The smart money is going to conclude
there indeed is "charge transfer" or current flow from fingertip to antenna and
this is not purely a field effect phenomena. The quantity
of current flow into and out from the gate lead is very small, but the amplification by the MOSFET supplies the microscope for observing such tiny current flow.
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watson.fawkes
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[*] posted on 7-1-2012 at 06:12


Quote: Originally posted by Rosco Bodine  
[...] a device called an IGFET (insulated gate field effect transistor) operating in enhancement mode, like an N-channel MOSFET. [...] The smart money is going to conclude
there indeed is "charge transfer" or current flow from fingertip to antenna and this is not purely a field effect phenomena.
It's called a field effect transistor because the transistor conducts solely because of the effect of field induced by voltage at its gate. There's no need for current flow across the air gap for this to happen. You even cited the name "field effect". Believe it. That name is there for a reason.

There's leakage current across the gate in real circuits, but it's in the fA range. That's femto-amperes, 10^-15, and that's a typical leakage current across many real-life (as opposed to ideal) insulators. There's also gate capacitance, which matters for AC signals and switching at high rates (in the kHz range and up), but that's not the situation you're describing.

Also, a MOSFET is a kind of IGFET. The reason there's another acronym is that the gate is now typically manufactured with polysilicon rather than metal (the M in MOSFET). But the term 'MOS' persists even when the 'M' isn't materially accurate, as in the CMOS, which uses both n-channel NMOS and p-channel PMOS devices, even when the gates are all polysilicon.
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Rosco Bodine
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[*] posted on 7-1-2012 at 10:32


The field of which you speak is concentrated locally and internally in the microsocopic structure of the semiconductor device as a result of a capacitance through a metal oxide insulating layer between semiconductor sandwich through which the current flows and the Gate. There has to be a transfer of electrons through the air in the experiment I described in order to accumulate the charge on the Gate. That charge will remain on the Gate for some time and leak down slowly just as an ordinary capacitor will leak down. But that charge on the gate
itself doesn't originate from field effect ......the current flow going through the
transistor of the FET type is only enabled and modulated by the local microscopic static or fluctuated field in the device itself.

Clearly, quantum mechanics is the international brotherhood of grease monkeys who work on old Volkswagens.


[Edited on 7-1-2012 by Rosco Bodine]
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watson.fawkes
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[*] posted on 7-1-2012 at 16:51


Quote: Originally posted by Rosco Bodine  
The field of which you speak is concentrated locally and internally in the microsocopic structure of the semiconductor device as a result of a capacitance through a metal oxide insulating layer between semiconductor sandwich through which the current flows and the Gate. There has to be a transfer of electrons through the air in the experiment I described in order to accumulate the charge on the Gate.
The electric field at the gate does not result from the capacitance, but because there electric potential at the gate is different than that in the channel. The fact that there's a capacitance is caused, instead, by the facts of charge mobility, insulation, and physical separation. The causation as you state it is exactly backwards.
Quote: Originally posted by Rosco Bodine  
There has to be a transfer of electrons through the air in the experiment I described in order to accumulate the charge on the Gate.
No, there doesn't. You're just wrong. Charges move under an electric field, and they don't have to move through a complete circuit in order to move. That's what dipole induction is. There's a transient current that flows in the wire connecting the gate and the test terminal. There's charge separation that's induced in that wire (a consequence of Gauss's Law for conductors), but the current in the wire does not induce a current in the air.

It appears you're missing some basic electromagnetic understanding. Any decent text on electromagnetic theory and Maxwell's equations covers this.
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[*] posted on 7-1-2012 at 17:45


I noticed that you can excite a field by moving an object, in this case a PVC tube in the general area of the electrodes, that is not coming between them, or within some arc above the direct path. You can be to the right of the discharge as in this example where the spark is triggered.
http://www.youtube.com/watch?v=6w_18SqA6x8

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Rosco Bodine
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[*] posted on 7-1-2012 at 18:21


If there wasn't existing a potential across the insulating barrier of oxide, then there would be no field, and that potential did not simply appear as a result of the field, the potential is precisely what causes the field. Indeed there is a circuit path from Gate to Drain but it is capacitive not just a resistive or ohmic circuit path. The Gate is not a
self-charging plate of a capacitor as if it were a spectator to the channel, and
there definitely is a deliberately placed circuit path for charge (electrons) to that Gate connection tab that is external
to the device. There is not an electromagnetic field which operates the FET but what causes the FET to conduct is instead an electrostatic field .....and the MOSFET is not a current amplifier but is a transconductance amplifier "translating" a voltage induced and static field into a static field intensity correlated current flow......even when there is no actual current flow through the Gate ....but only a static potential with an associated field strength of static nature. If the movement of charge to the Gate is not external to the device through space, air, or conductor providing the pathway for the movement of "charge" then such charge would have required tunneling from the channel semiconductor, or teleportation, or the intercession of elves.

The behavior of a MOSFET is somewhat analogous to the Hall effect, but the modulating force is electrostatic field strength rather than magnetic or electromagnetic field strength, and the quantity being modulated is current rather than voltage.

Just like a Hall effect device needs externally sourced magnetic field as stimulus resulting in a Hall effect voltage, so does the MOSFET need externally sourced current flow to build the field which becomes electrostatic as the Gate accumulates a charge corresponding to a given potential
and enables a correlated current flow through the channel.

To cause further aggravation and unsettle everyone completely ......I must confess that the experiment I described was a bit of friendly intellectual provocation and the current flow from the positive lead to antenna lead is not a flow of electrons at all but of course is a traversing of space by "holes" :D

What are electrons good for unless there is found a hole in which to put every one of them ?

[Edited on 8-1-2012 by Rosco Bodine]
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[*] posted on 7-1-2012 at 22:41


Is this the same author that posted this here _
http://www.sciencemadness.org/talk/viewthread.php?tid=18463


There is a proportionality that should be noted , the electric force is
1,000,000,000,000,000,000,000,000,000,000,000,000 times
stronger than gravity. If you want to separate a mass of ionic salt
equivalent to your own weight into it's ions by the same distance
that you can separate yourself from the earth by jumping say 2 feet
this would require force sufficient to peel off a tectonic plate off the
surface of the earth. Good trick if you can manage it.

.
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Rosco Bodine
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[*] posted on 7-1-2012 at 23:55


franklyn,

http://en.wikipedia.org/wiki/Gustav_Kirchhoff

http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws

http://en.wikipedia.org/wiki/Charles-Augustin_de_Coulomb

http://en.wikipedia.org/wiki/Coulomb

In the world of relativity is there any positivity but for want of negativity, or is there any negativity but for want of positivity ? Equilibrate, now there's a balance so entropic! :D

[Edited on 8-1-2012 by Rosco Bodine]
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franklyn
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[*] posted on 8-1-2012 at 04:28


weight of person = 150 pounds

150 pounds X .454 = 68 kilograms = 68,000 grams

gram molecular weight of
Sodium = 23
Flourine = 19
Sodium Fluoride = 42

68000 / 42 = 1619 moles of NaF

Avogadro's number
http://en.wikipedia.org/wiki/Avogadro%27s_number

Faraday unit of charge is Avogadro's number of charges
600,000,000,000,000,000,000,000
or 96485 Coulombs

96485 Coulombs times 1619 moles comes to 156,209,215

from the link provided
http://en.wikipedia.org/wiki/Coulomb
In everyday terms
" two point charges of +1 C, placed one meter apart, would experience a repulsive force of 9,000,000,000 N,
a force roughly equal to the weight of 920,000 metric tons of mass on the surface of the Earth."

156,209,215 times 920,000 metric tons of mass on the surface of the Earth = one tectonic plate. 143,712,477,800,000 metric tons


Mind you this is only approximate. My example of 2 feet is just 61 % the distance of one meter
in the example quoted from wikipedia. The force being inverse to the square of the distance
means it would actually be quite a lot greater. In my example the force is attractive in the
wikipedia example the force is repulsive.


Crust density is perhaps 3 tons per cubic meter

143,712,477,800,000 divided by 3 is ~ 47,900,000,000,000 cubic meters

cube root of 47,900,000,000,000 is ~ 36300 meters , a cube 36.3 kilometers on the side.

mean thickness of oceanic crust is about 9 kilometers thick , 36 divided by 9 is 4
carving the cube into four 9 kilometer slices forms a 9 kilometer thick plaque 72 kilometers
on the side.

An area about the size of that which colapsed to generate the magnitude 9.3 earthquake
in the indian ocean that generated the resulting infamous tsunami in December 2004.
It altered the polar moment of the earth increasing the rotation a millionth of a second.

The energy involved is guessed to have been around 475,000,000 tons of TNT.
http://earthquake.usgs.gov/earthquakes/eqinthenews/2004/us20...
More than the entire yield of W-53 warheads of all Titan II missiles that were
deployed in the early 1980's. ( 50 W-53 each yielding 9 megatons , is 450 )

A kilogram of TNT is rated at 4.27 Megajoules. A metric ton is 1000 kilograms.
This imagined capacitor weighing something more than 150 pounds , allowing
for a dielectric barrier to separate the charge , would store 4.27 X 300 = 1,281
quintillion Joules. ( 1,281,000,000,000,000,000 ) or 1. 28 sextillion

As I said , nice trick if you can manage it.
.

[Edited on 9-1-2012 by franklyn]
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watson.fawkes
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[*] posted on 8-1-2012 at 08:12


Quote: Originally posted by Rosco Bodine  
If there wasn't existing a potential across the insulating barrier of oxide, then there would be no field, and that potential did not simply appear as a result of the field, the potential is precisely what causes the field.
More drivel. The potential doesn't cause anything, because it doesn't always exist. The potential is a conceptual abstraction that exists only when there's not a time-varying magnetic field. It is perfectly ludicrous to say that a human concept causes the field sometimes, when the magnetic field is fixed, but then stops causing it when the magnetic field is not. Again, this is yet more evidence that you really don't understand this subject particularly well.
Quote:
If the movement of charge to the Gate is not external to the device through space, air, or conductor providing the pathway for the movement of "charge" then such charge would have required tunneling from the channel semiconductor, or teleportation, or the intercession of elves.
Apparently you didn't actually read my last post on this subject, or if you did, you didn't understand it. There's charge on the gate that's induced from the test lead acting as an antenna. There's electron motion within the antenna and gate that moves so that the electric field within those conductors is zero. That's Gauss's Law in action.
Quote:
Just like a Hall effect device needs externally sourced magnetic field as stimulus resulting in a Hall effect voltage, so does the MOSFET need externally sourced current flow to build the field which becomes electrostatic as the Gate accumulates a charge corresponding to a given potential and enables a correlated current flow through the channel.
Wrong again, and from a lack of basic knowledge this time. There can be field between the gate and channel, across the gate insulator, in the complete absence of any source-drain current. The field effect is present even when no device current is flowing. This is a fundamental fact of these devices.

There's a good treatment of MOSFET device behavior in Sedra & Smith's Microelectronic Circuits, as well as many other undergraduate textbooks. I recommend you read one.
Quote:
To cause further aggravation and unsettle everyone completely ......I must confess that the experiment I described was a bit of friendly intellectual provocation and the current flow from the positive lead to antenna lead is not a flow of electrons at all but of course is a traversing of space by "holes" :D
Wrong again, and in two different ways. Minority carriers ("holes") are a feature of semiconductors, not of metals. The transient antenna current travels through metals. The semiconductor material in a MOSFET is between the source and drain, and doesn't participate. And second, as I've stated before, there's not any kind of current flow in the air that terminates on the antenna.
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Rosco Bodine
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[*] posted on 8-1-2012 at 11:08


Potential does exist across the source which is the battery, and the potential originating across the battery exists with potential drops across and is transferred and felt by device components in the circuit through the conductive paths available, and through the semiconductive and capacitive and inductive paths present.

If not minority carriers then protons, and if neither, then tunneling does occur...
otherwise there is no circuit or current flow and Kirchoff's laws are violated.
A capacitor stores potential as an electrostatic field and no current flows unless the intensity of that electrostatic field is changing, that flux necessarily coexists with electrical current flow, or otherwise the field is completely static, the field
is still there but unchanging and no current flows.

You are describing a static magnetic field and electrostatic field interchangeably as if they are equivalents, as if the elementary particles are both stationary (static) and yet are moving at the same time, movement which is required for an electromagnetic type of magnetic field, but is not a property of an electrostatic field which does exist for stationary elementary particles.

There's an easy enough way to resolve this argument by performing the experiment in a glove box and varying the atmosphere.....see what effect humidity or an aerosol of salt water has on the rise time for the gate via its antenna.
Or even forget the glove box, just exhale a breath of moist air through the space between the fingertip and the test clip. Anyway, the effect is seen that the Gate of the MOSFET
will behave as something like a "megger" with regards to the air gap, and honestly I have not put this through its experimental paces to completely analyze the effect which can be observed ....but it does appear the air gap is ohmic and is conductive even if at an infinitesimal level of conductivity ....it is still enough conductivity for the MOSFET
to react. There is still very much present a field and I believe also probably an actual current flow of elementary particles of charge of whatever character and polarity occurring....
and it is the same microscale effect but involving DC current flow as would be be more spectacularly seen by the excitation of a fluorescent tube held in the hand in the field gradient near a tesla coil, or in the vicinity of high tension transmission lines.

On a somewhat related note here's some theremin samples

http://www.youtube.com/watch?v=Ptq_N-gjEpI Claire de Lune

http://www.youtube.com/watch?v=K6KbEnGnymk Over the Rainbow

[Edited on 8-1-2012 by Rosco Bodine]
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watson.fawkes
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[*] posted on 8-1-2012 at 13:29


Rosco Bodine's responses are so chock full of gibberish that I can't make sense of them. So I'll just address the claims that are clearly wrong.
Quote: Originally posted by Rosco Bodine  
If not minority carriers then protons, and if neither, then tunneling does occur...
otherwise there is no circuit or current flow and Kirchoff's laws are violated.
Kirchoff's circuit laws don't apply to the antenna because it doesn't satisfy the assumptions required for these laws to apply, which is that there aren't induced circuit potentials from electromagnetic fields. Kirchoff's laws apply when all the potentials are entirely generated and contained within the circuit.

You can fantasize a conductor on the other side of the antenna to make a circuit, but that would make it the analysis of a fantasy and not of reality. In terms of circuit analysis, you can model an antenna as a voltage source to fixed potential (ground), but that's an equivalent circuit, not an actual circuit. So the equivalent circuit is a fantasy that yields the same analytical results, but it's a mistake to assert that there's current flow on the other side of the antenna just to satisfy narrow-minded circuit assumptions where the physical device doesn't have the loop required to make a circuit.

I learned this rather clearly last year when I was digging into the theory behind induction heating. The work coil at the business end of such a device is dumping electromagnetic energy into the work piece in order to heat it. In order to do so, it uses an AC current through the work coil, yet that work coil does not naively satisfy Kirchoff's law because there's an induced circuit potential across it from the back-reaction of the induced current in the work piece. So this circuit doesn't satisfy Kirchoff's voltage law. In order to get an equivalent circuit to analyze, you have to model that back-induced field with a voltage source or, alternately, a resistor, whose value varies with the load. (The inductance of the work coil also changes, incidentally.) As soon as you have interaction effects that are outside the circuit you have to do some proper physics in order to get an equivalent circuit suitable for analysis. The point is that non-satisfaction of Kirchoff's laws, while not exactly common, isn't at all restricted to the present example.
Quote:
There's an easy enough way to resolve this argument by performing the experiment in a glove box and varying the atmosphere.
If you do the experiment in vacuum, where there's no conductor at all, you'd still get almost exactly the same result as if you do it in air. And if you want to claim quantum tunneling, it will expose your ignorance about tunneling current rates across a 1 cm gap, which are so small as to be reasonably considered non-existent. The difference between air and vacuum is due to the polarization of the medium. The greater the polarization, the closer the potential at the MOSFET gate to that of the fixed potential terminal (the battery, in the example). A metal wire can be considered an infinitely polarizable medium, but even in the absence of any medium at all, that is, vacuum, there's still an induced potential at the antenna.
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[*] posted on 8-1-2012 at 13:50


Okay wise guy, what would be the effect of a blocking diode in the test lead from the positive battery terminal ? Simply clip a diode reverse polarity to easy forward current flow in the clip lead and grab the free end of the diode with one hand and point the finger of the other hand at the end of the antenna lead to the gate. Since there is no current flow according to you then the blocking diode should have no effect. You acknowledged earlier that there is a transient current flow involved as the gate potential changes. Do you you really think one end of the wire test lead attached to the gate has a polarity opposite the end of that clip lead attached to the Gate? There may be a slight ohmic drop there
but definitely not any significant potential difference. That potential change on the gate must arise from electron deficiency which occurs by electrons leaving that gate through the antenna and those electrons do not simply pile up at the end of the test lead and just park there .....
they are traversing the air space to your fingertip and through your body to the positive terminal of the battery, making, completing a thing called a circuit.

There is no need to fantasize anything on the other side of the oxide layer insulating the gate as a dielectric of a capacitor, that thing on the other side is the channel.
And Kirchoff's laws definitely do apply and there are no assumptions or models you can propose which credibly illustrate how Kirchoff's laws somehow do not apply to what is indeed a closed circuit system.....closed through the airgap
abstractly as it may be .....it is still a closed circuit.

There is another plausible angle on this scenario, but it seems a stretch .....that the end of the test lead antenna could behave as a plate of a capacitor, the airgap is the dielectric and the fingertip behaves as the other plate of the capacitor. In such case there plausibly could be some piling up of electrons at the end of the antenna lead. Is this what you are getting at, capacitive coupling? If so, then what replenishes the charge lost to leakage current?

Lost ......what a word huh

http://www.youtube.com/watch?v=X5kRipK8GjI

[Edited on 8-1-2012 by Rosco Bodine]
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Morgan
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[*] posted on 8-1-2012 at 15:15


Antenna/capacitor tidbit.

http://vimeo.com/2814718

"The theremin is almost unique among musical instruments in that it is played without physical contact. The musician stands in front of the instrument and moves his or her hands in the proximity of two metal antennas. The distance from one antenna determines frequency (pitch), and the distance from the other controls amplitude (volume). Most frequently, the right hand controls the pitch and the left controls the volume, although some performers reverse this arrangement. Some low-cost theremins use a conventional, knob operated volume control and have only the pitch antenna. While commonly called antennas, they are not used for receiving or broadcasting radio frequency, but act as plates in a capacitor."
http://en.wikipedia.org/wiki/Theremin
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Rosco Bodine
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[*] posted on 8-1-2012 at 17:04


Oh I'm a little capacitor plate short and stout,
my left hand my source path, my finger the spout,
There sits a MOSFET ...what's it Gate about ?
It pulls my finger and its charge comes out :D
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watson.fawkes
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[*] posted on 8-1-2012 at 17:16


Quote: Originally posted by Rosco Bodine  
That potential change on the gate must arise from electron deficiency which occurs by electrons leaving that gate through the antenna and those electrons do not simply pile up at the end of the test lead and just park there .....
Yes, they do. That's what an induced dipole is. You put a conductor in an electric field and you get charge rearrangement. This is freshman physics.

Since you have proven yourself ignorant, arrogant, and lazy, I looked up a physics lecture that explains this. The picture of charge rearrangement in a conductor in a external field is on the second page. http://web.mit.edu/sahughes/www/8.022/lec05.pdf
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Rosco Bodine
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[*] posted on 8-1-2012 at 18:11


You are failing to account for the leakage current. There is a makeup current flow which has to be occurring, and surpassing the leakage current in value in order for a sufficient gate charge potential to be maintained, or increased, and the only path for that current flow is through the air gap. If you move your finger and increase the gap to a certain distance, the charge on the Gate will gradually dissipate and equilibrate with the channel and the MOSFET will stop conducting .....it will gradually turn off.

The MOSFET is not getting something for nothing although the current is small it is present and it is greater than the leakage current or else the charge on the gate could not be accumulated from the signal supplied to that Gate.

If you think about the capacitive coupling concept which is in actuality and truth what you are proposing is the explanation, you find difficulty with that concept because once the capacitor is charged .....current flow stops. And when that charging current stops then the leakage current would gradually dissipate the potential on the Gate and turn off the MOSFET.

But there is leakage current also in a capacitor ....through the dielectric because no insulator is really quite perfect.
And if the dielectric is an airgap .....what would you suppose is the medium through which the leakage current through the airgap is flowing? Duh .....maybe air.

http://www.youtube.com/watch?v=5a_4fBH_7dk If

http://www.youtube.com/watch?v=wK94mZ465LI Freedom


[Edited on 9-1-2012 by Rosco Bodine]
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