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Author: Subject: Static Electricity
Lambda
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[*] posted on 27-6-2005 at 11:34
Triboelectric discharge


I remember an experiment in which Triboelectric discharge was involved.

When you grind ordinary white crystal sugar in a mortar with a pestill in the dark, then you see light flashes. This phenomenon is due to the breakage of the crystal lactic, thus releasing energy in the form of visible light. Piezo-materials allso behave in a similar manner, but then more focust on lactic-deformation, than rupture.

Saps, are you refering to this phenomenon ?
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saps
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[*] posted on 27-6-2005 at 15:26


***Sry... what i originally meant was: when considering thier useable surface area and positions in the triboelectric series what 2 materials most eficiently produce a negative charge??
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[*] posted on 28-6-2005 at 14:18


According to the search done with Yahoo (triboelectric series) the 3 best materials to generate a negative charge are Vinyl(PVC) , Silicon and Teflon.
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[*] posted on 28-6-2005 at 18:40


Geez, just Google it.

http://www.rfcafe.com/references/electrical/triboelectric_se...

Farther away they are, the more potential made. K?

Tim




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Marvin
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[*] posted on 29-6-2005 at 13:49


Does it bother anyone else that sulphur and polyethylene are on the list twice each in different positions?
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[*] posted on 29-6-2005 at 17:08


Quote:
Originally posted by Chris The Great
[Let me explain. Yes, there is an electrical field between the two poles of the battery. However, that doesn't cause the battery to have a voltage realative to other things. You would need to ground one end to bring the other end to have a high potential towards other things, as the ground has a voltage of 0.


The poles of a battery do have a voltage relative to "other things".

If you touch a charged sphere hanging in the air, you get a shock because it has a voltage relative to the ground, even though it is just a sphere hanging in the air.

It has a voltage relative to the ground thanks to its capacitance to ground (in other words, the way its electric field interacts with the ground). In the same way the poles of a battery have a capacitance to ground and its electric field interacts with the ground. Since the voltage and capacitance involved are small the affect is hard to notice.

If a battery had poles of the same sort of area and voltage as the original charged sphere, you could experience a shock from at least one of the poles.
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[*] posted on 29-6-2005 at 17:30


Sure, the poles of a battery can have a voltage relative to "other things". But, there is no reason for them to have such a voltage unless they are somehow linked to said other things. A battery is a closed system, untill you attach it to something else. A sphere can have a charge, but it needs to interact with its surroundings to get that charge. Same with a battery.

If you suspend either a sphere or a battery, without charging it *relative to ground* it will have no charge, to you, untill you are connected with one of the battery's poles.

To have fieldstrength mean anything, it has to be relative to something, eh? A cloud doesn't need to be grounded to make lightning -- a charge has built up and then is released.




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neutrino
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[*] posted on 29-6-2005 at 18:38


The standard reference point in these cases is zero, the potential/field strength at infinity.

Think about it this way: both poles can’t be neutral.
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[*] posted on 29-6-2005 at 19:32


This is both more difficult and easier than it looks. In the first part field strength does not have to be relative to anything, its change in potential over distance, ie a derivitive.

There is nothing to stop a field/potential existing between a battery terminal and ground but its not possible to say what this is, it depends on everything else. Batteries arn't electrostatic, they are electrodynamic.

In electrostatics its easy to define what ground is, as matter starts off neutral.
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[*] posted on 30-6-2005 at 05:20


Ok, Marvin, I guess I misspoke (mistyped?) myself slightly. When I said it has to be relative to something, I meant more that it need to differ in potential from something, else there is no change in potential so no field.

Neutrino, I take it you are saying something like, since there is a potential difference between the two poles, then only one can be the ground reference if indeed either is. So the minimum possible potential at one pole, is if the battery is exactly net neutral, therefore a pole is +or- E/2 with respect to ground.

I see what you are saying, and I have to admit it seems to be right... :P




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neutrino
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[*] posted on 30-6-2005 at 07:45


Couldn't batteries be considered electrostatic also? The battery is going to pump some electrons from the positive terminal to the negative, creating a pair of point charges. There wouldn’t be much charge, as I said earlier, but it would be there.
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[*] posted on 30-6-2005 at 13:39


Exactly. The ONLY difference between common direct current and static electricity is the scales of voltage and current. A Zamboni pile stacked to say 20,000 will easily blur that difference. ;)

Tim




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[*] posted on 30-6-2005 at 15:24


Quote:

Batteries arn't electrostatic, they are electrodynamic.

Electrodynamics is electricity that's moving, electrostatics is electricity that isn't. It's the same electricity and the same voltage, charge, capacitance and resistance.

Neutrino is quite correct in saying that if there is a pd between the terminals of the battery (which you'd hope so), then they can't both be neutral. That is what I was referring to in my post when I said you would have to experience a shock from at least one of the terminals if the voltage were high enough.

To avoid confusion, I'll clarify that I'm not saying the voltage to ground has anything to do with the emf of the battery beyond this fact.

[Edited on 30-6-2005 by Simon]
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Marvin
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[*] posted on 30-6-2005 at 15:29


A battery isnt a source of potential, its a source of relative potential between two conductors. Whats more essentially unlimited charge is allowed to flow between them in order to maintain it. This doesnt square very easily with classical electrostatics where voltages are assumed to result from charge, rather than the other way around.


Simon,

"Electrodynamics is electricity that's moving, electrostatics is electricity that isn't."

A battery is an electrodynamic element, its only meaningful when current is flowing. While its true to say there is a charge difference between the terminals in the static state, it isnt possible to say what those charges actually are. If you replace those elements by charged terminals you can have the same EMF between them, but the problem now always has a solution. The item is nolonger a battery, but the only difference occurs when things actually change.

"It's the same electricity and the same voltage, charge, capacitance and resistance. "

Resistance is not meaningful unless current is flowing so its not right to argue that an electrostatic picture contains the same basic elements.

"Neutrino is quite correct in saying that if there is a pd between the terminals of the battery (which you'd hope so), then they can't both be neutral. "

Of course they can both be neutral, just not at the same time.

"That is what I was referring to in my post when I said you would have to experience a shock from at least one of the terminals if the voltage were high enough. "

The voltage does not come into it, assume you are neutral, charge will flow but the amount also depends on the capacitance of the electrodes. This could be anything and the shock itself is of course dynamic flow that has nothing to do with the actual battery.


[Edited on 30-6-2005 by Marvin]
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[*] posted on 30-6-2005 at 16:15


Ideally yes, but when you observe a battery for a long period of time, the zinc is eventually consumed and it runs out of <I>charge</I>.

Neat thing about electrochemistry and electrostatics...both work on individual electrons like that.

Tim




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[*] posted on 30-6-2005 at 16:24


Quote:
Originally posted by Marvin
The voltage does not come into it, assume you are neutral, charge will flow but the amount also depends on the capacitance of the electrodes. This could be anything and the shock itself is of course dynamic flow that has nothing to do with the actual battery.

The voltage of the battery does come into it in a sense, while it is still not the same voltage as the voltage to ground. Otherwise this quote doesn't contradict anything I've written, so we seem to be mostly in agreement. Same goes for most of the rest of what you wrote.

The difference seems to be in the idea that there is something specially different about static electricity and dynamic.
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[*] posted on 30-6-2005 at 18:20


The battery example came up because the concept of isolated circuits was being applied in electrostatic terms. In electrostatics isolated circuits (in which a voltage needs a point in the same circuit to be relative too in order to have any meaning), capacitors, batteries, inductors and resistors do not exist.

The idea that theoretically a battery must give a shock from one or the other terminal is false. If you take an ideal battery you can assume the capacitance of the terminals is zero. We can touch one terminal assuming we are ground and regardless of battery voltage no current needs to flow - we do not get a shock. If we then let go and touch the other terminal even though the official polarity is now switched still no current needs to flow. In the real world capacitance is unavoidable and with an EHT battery a shock could be felt but this effect is almost solely caused by other factors.

While a battery can be a source of static electricity, from a purely electrostatic viewpoint it does not exist.
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[*] posted on 30-6-2005 at 18:38


Yes, my point was that we don’t exactly live in an ideal world and a few extra electrons are going to lie at the negative terminal and a few will be missing from the positive. I guess I really should start explaining my ideas a little better.
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[*] posted on 1-7-2005 at 17:38


This is getting idiotic.:(

The original statement was that the terminals of the battery have no voltage "relative to other things", unlike a charged sphere.

I pointed out that there is nothing special about the battery and that all things have a relative potential, even if that is 0.00V, thanks to capacitance.

In other words the interaction from electric fields.

In yet other words, the integral of the electric field intensity across distance.

Accepting this leaves everything unified and integration a safe pastime. You can call a particular capacitance negligable, but saying it doesn't exist is theoretically unsound and leads to problems which are unneccessary, since there is always capacitance.
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