| Pages:
1
2 |
Lambda
National Hazard
Posts: 566
Registered: 15-4-2005
Location: Netherlands
Member Is Offline
Mood: Euforic Online
|
|
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 ?
|
|
|
saps
Hazard to Self
Posts: 82
Registered: 7-3-2005
Location: New Britian
Member Is Offline
Mood: disgruntled
|
|
***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??
|
|
|
Archimede
Harmless
Posts: 33
Registered: 13-5-2005
Member Is Offline
Mood: No Mood
|
|
According to the search done with Yahoo (triboelectric series) the 3 best materials to generate a negative charge are Vinyl(PVC) , Silicon and Teflon.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Geez, just Google it.
http://www.rfcafe.com/references/electrical/triboelectric_se...
Farther away they are, the more potential made. K?
Tim
|
|
|
Marvin
National Hazard
Posts: 995
Registered: 13-10-2002
Member Is Offline
Mood: No Mood
|
|
Does it bother anyone else that sulphur and polyethylene are on the list twice each in different positions?
|
|
|
Simon
Harmless
Posts: 9
Registered: 28-6-2005
Member Is Offline
Mood: Subjunctive
|
|
| 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.
|
|
|
Oxydro
Hazard to Others
Posts: 152
Registered: 24-5-2004
Location: NS, Canada
Member Is Offline
Mood: distracted
|
|
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.
"Our interest's on the dangerous side of things" -- Browning
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
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.
|
|
|
Marvin
National Hazard
Posts: 995
Registered: 13-10-2002
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
Oxydro
Hazard to Others
Posts: 152
Registered: 24-5-2004
Location: NS, Canada
Member Is Offline
Mood: distracted
|
|
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... 
"Our interest's on the dangerous side of things" -- Browning
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
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.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
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
|
|
|
Simon
Harmless
Posts: 9
Registered: 28-6-2005
Member Is Offline
Mood: Subjunctive
|
|
| 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]
|
|
|
Marvin
National Hazard
Posts: 995
Registered: 13-10-2002
Member Is Offline
Mood: No Mood
|
|
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]
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
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
|
|
|
Simon
Harmless
Posts: 9
Registered: 28-6-2005
Member Is Offline
Mood: Subjunctive
|
|
| 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.
|
|
|
Marvin
National Hazard
Posts: 995
Registered: 13-10-2002
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
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.
|
|
|
Simon
Harmless
Posts: 9
Registered: 28-6-2005
Member Is Offline
Mood: Subjunctive
|
|
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.
|
|
|
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
