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Author Topic: Physics question
nerdwithnofriends
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Icon 1 posted November 30, 2006 00:36      Profile for nerdwithnofriends     Send New Private Message       Edit/Delete Post   Reply With Quote 
Hey physics geeks, I have a question that will probably seem very simple for you:

How do you determine the force on a charged particle exerted by a plate of a given area (square metres) with a given potential (volts)? Does this even work, since I thought voltages were measured relative to two points?


I know coulombs law for determining the force between two charged particles, and I've been on the Wikipedia for hours researching the the effects of a charged particle in electrostatic, magnetic, and electromagnetic fields. (Here's a list of the tabs I have open in another window right now: Electric Field, Volt(unit), Lorentz Force, Magnetic Field, Tesla(unit), and Potential Difference).

However, these formulae seem to be only helpful when you already know the force exerted on our imaginary particle of arbitrary charge.

I've taken extensive notes for use later, when it seems the Lorentz Force equation will come in handy, but until then I'm stuck.

I'm sure it's right in front of me and I can't see it, but I'm really struggling.

If you're curious, this isn't for homework, but for a device I'm going to try to build (on the cheap) to give me something to do here.

Thanks in advance!

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"The Buddha, the Godhead, resides quite as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain or in the petals of a flower." - Robert M. Pirsig

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TheMoMan
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Icon 1 posted November 30, 2006 03:00      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
nerdwithnofriends________________This could become quite a project. The MoMans thoughts, set up your experiment to measure the forces in the Vertical axis (Z) this will help negate soom of the other effects. Get some very good insulaters to prevent flash over in case the voltages have to go very high. Now hang a conductive string some what like a plumb bob, ask a plumber or electrician. Weigh your plumb-bob energise the system and watch the scale. As you increase voltage the plumb should show force (weight) gain. to negate Tides the experiment should run 24/7 untill you have observed a full lunar cycle and of course 28 solar cycles. Now change voltage and repeat untill you are sure that you have ruled out all out side forces, compare to the info from known constants, and then publish your findings.

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Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
The Famous Druid

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Icon 1 posted November 30, 2006 03:09      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
If you need to ask, you shouldn't be doing it !

Elec-trickery is dangerous stuff, I've worked in a couple of places that used serious electrical stuff, and the guys who knew what they were doing did a very good job of convincing me to ...leave... ...those... ...things... ...alone.

--------------------
If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

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quantumfluff
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Icon 12 posted November 30, 2006 08:10      Profile for quantumfluff     Send New Private Message       Edit/Delete Post   Reply With Quote 
Oh, what's the big deal. The worst that could happen is the house vanishing in a puff of smoke. I don't think any home experiment would take out the grid.
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TheMoMan
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Icon 1 posted November 30, 2006 10:12      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
The Famous Druid_____________________I understand your fear however I was raised in a house with an electrical engineer, so it was not long before I was shocked. If Nerdwithnofriends does his experiment on a plastic table and uses a power supply with a bleeder resister, and waits for the bleeder resister to do its job, he should be safe. That said can I be the benificiary?

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Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
nerdwithnofriends
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Icon 1 posted November 30, 2006 10:56      Profile for nerdwithnofriends     Send New Private Message       Edit/Delete Post   Reply With Quote 
I appreciate the concern TFD, but this shouldn't be too terribly dangerous. I've already figured out how most of the apparatus will work. The total amount of power dissipated won't be ridiculous- no more than a few watts for the first run. So, a very high-potential transformer will be used for the system, but the current will be tiny. I can pick up a used neon display power supply for about $20.00 US, which will give me 4000 volts of DC current at a couple of milliamps, which should be just what I need.

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"The Buddha, the Godhead, resides quite as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain or in the petals of a flower." - Robert M. Pirsig

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Ashitaka

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Icon 1 posted November 30, 2006 11:19      Profile for Ashitaka     Send New Private Message       Edit/Delete Post   Reply With Quote 
I assume you are trying to repeat Millikins oil drop expirenment, Have you been to Wiki's page on the oil drop expiriments?

This page has better explanations than I could give and the needed equations.

But here is your basic answer.

follow me...
volts = watts / Amps
so

V = (m^2 * kg) / (s^3 * A)

A = amps = 1 Coulomb / second

so

V = m^2 * kg / s^2 * C <- the seconds from the amp cancels out.

If you multiply this by one coulomb , C cancels out and your get

m^2 * kg / s^2

This is not force but moment of force, newtons times meters. Force would be dividing this by the distace from the plate. The answer you are looking for. I think.

Chemistry rules!!

ps
Voltages are measured between two points but that doesn not mean the voltage is equal between the two points. Actually the voltage will differ greatly if the medium between the two point is not uniform, which greatly affects the speeds of charges particles whithin, This property of voltage is a double edged sword in trying to get good seperation in electrophoresis.

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"If they're not gonna make a distinction between Muslims and violent extremists, then why should I take the time to distinguish between decent, fearful white people and racists?"

-Assif Mandvi

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The Famous Druid

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Icon 1 posted November 30, 2006 12:08      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by nerdwithnofriends:
...this shouldn't be too terribly dangerous...

Famous last words.

...a very high-potential transformer will be used for the system, but the current will be tiny. I can pick up a used neon display power supply for about $20.00 US, which will give me 4000 volts of DC current at a couple of milliamps...

There was an article in the local rag yesterday about a worker who was electrocuted while changing the tube on a neon sign.

Ok, maybe I'm paranoid, but I've worked in the kind of place where you learn what a Faraday Suit is. They did a good job of putting the fear of The Flying Spaghetti Monster into me about electrickery.
There are old linesmen, and bold linesmen, but there are no old bold linesmen.

--------------------
If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

Posts: 10680 | From: Melbourne, Australia | Registered: Oct 2002  |  IP: Logged
nerdwithnofriends
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Icon 1 posted November 30, 2006 12:27      Profile for nerdwithnofriends     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Ashitaka:
I assume you are trying to repeat Millikins oil drop expirenment, Have you been to Wiki's page on the oil drop expiriments?

This page has better explanations than I could give and the needed equations.

But here is your basic answer.

follow me...
volts = watts / Amps
so

V = (m^2 * kg) / (s^3 * A)

A = amps = 1 Coulomb / second

so

V = m^2 * kg / s^2 * C <- the seconds from the amp cancels out.

If you multiply this by one coulomb , C cancels out and your get

m^2 * kg / s^2

This is not force but moment of force, newtons times meters.

In other words, Joules, or units of energy. This is what I had initially thought the way to solve the problem would be. However, this seems inherently wrong, since the force between two charged particles is an inverse square function.

Determining the energy used accelerating a particle is an important part of my problem, but I was just going to integrate force as a function of distance over the distance travelled to get units of energy.

Of course, if I could determine the amount of energy used, maybe I could derive that with respect to distance to give me a force value I can use in the Lorentz function.

--------------------
"The Buddha, the Godhead, resides quite as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain or in the petals of a flower." - Robert M. Pirsig

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littlefish
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Icon 1 posted November 30, 2006 12:33      Profile for littlefish   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
Remember, volts jolt, mills kill.

A quick googling shows that 70 mA is generally taken as lethal. Tasers run in single mA figures.

Personally I wouldn't be happy "experimenting" with things powered by the mains. You can get monster high voltages with tiny amperages safely through static.

Posts: 2421 | From: That London | Registered: Nov 2001  |  IP: Logged
nerdwithnofriends
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Icon 1 posted November 30, 2006 12:48      Profile for nerdwithnofriends     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by littlefish:
Remember, volts jolt, mills kill.

A quick googling shows that 70 mA is generally taken as lethal. Tasers run in single mA figures.

Personally I wouldn't be happy "experimenting" with things powered by the mains. You can get monster high voltages with tiny amperages safely through static.

Yes, but I don't have a van DeGraff (sp?) generator handy, so that's out of the question.


Don't worry guys, I've done stuff like this before; I've just never been concerned with the math behind it, so that's why I'm asking this. It's not like I'm going to be touching the device while it's running. Insulated surfaces, grounding straps where necessary, all that jazz will be set up properly. I'm not going to die! (knock, knock).

--------------------
"The Buddha, the Godhead, resides quite as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain or in the petals of a flower." - Robert M. Pirsig

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TheMoMan
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Icon 1 posted November 30, 2006 13:31      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
nerdwithnofriends___________________Since you live in North America look into getting an ignition transformer from an old oil furnace, they deliever about 20kv then scrounge up a rectifier from an old TV of over 21 inch. then the rectifier will have enough inverse voltage rating to not fry during your experiment.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
nerdwithnofriends
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Member # 3773

Icon 1 posted November 30, 2006 18:17      Profile for nerdwithnofriends     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by TheMoMan:
nerdwithnofriends___________________Since you live in North America look into getting an ignition transformer from an old oil furnace, they deliever about 20kv then scrounge up a rectifier from an old TV of over 21 inch. then the rectifier will have enough inverse voltage rating to not fry during your experiment.

What about using an automotive ignition coil run off of a rectivied ~12vdc line? That would be easier to come by.

I'm thinking a used microwave oven might have a coil I could use to generate the voltage I need, then all I need to do is find a way to rectify it, I'll probably use the TV rectifier like you said... it should be easy to get one of those.

--------------------
"The Buddha, the Godhead, resides quite as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain or in the petals of a flower." - Robert M. Pirsig

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TheMoMan
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Icon 1 posted December 01, 2006 03:33      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
nerdwithnofriends________________Now we are getting some where.

Ignition coil with car battery turn signal blinker and condenser, 45000+Volts

Microwave transformer 3000+Volts too many watts too deadly.

If you have worked arounf the second anode on a CRT Moniter or TV usually 1000 Volts/inch of diagonal measure.

If you go with the ingnition coil I do not know where you could get a recifier that can handle those kind of voltages, However a spark plug in the high voltage lead would allow your scales wire and plumb-bob to hold the voltage (the sparking would stop when the objects being charged reached almost coil potential. You then would need a discharge method to get the charge off of tour apporatus. You would not need a rectifier with the coil because most of the energy will be at magnetic field colapse.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
TheMoMan
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Icon 1 posted December 02, 2006 04:03      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
nerdwithnofriends___________________Please post at least daily with your health status so that we may know that you have lived through these experiments.

Also read up on crowbar circuits they are quite usefull for this type of thing we used them to discharge Lasars.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged


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