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What is Voltage

by kaotak
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kaotak
#1
Apr21-07, 09:11 PM
P: n/a
What is voltage? So many words, so many explanations are just hollow echoes off the walls of "authoritative sources"

What is voltage? Why does everything electrical we see give its voltage? Does it cause current to flow? If so, how? Because of electric forces? How do we harnest the energy from our power outlets? Where are the positive and negative terminals on our power outlets? Don't all voltage drops need positive and negative terminals?

What does it really DOOOOOOOOO.

Does it give us current? If so, how?

Where does the current come from? Where do we get the energy?

Electromagnetism makes no sense.
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interested_learner
#2
Apr21-07, 09:24 PM
P: 214
Another name for voltage is potential. In other words, potential energy. It is like being on top of a hill and current is like rolling balls off the top of the hill.

Ok not quite, but does someone have a better analogy?
kaotak
#3
Apr21-07, 09:34 PM
P: n/a
Quote Quote by interested_learner View Post
Another name for voltage is potential. In other words, potential energy. It is like being on top of a hill and current is like rolling balls off the top of the hill.

Ok not quite, but does someone have a better analogy?
Where do the balls (current) come from?

russ_watters
#4
Apr22-07, 12:45 AM
Mentor
P: 22,239
What is Voltage

You've used magnets before, right? You've felt the force...?
vanesch
#5
Apr22-07, 02:06 AM
Emeritus
Sci Advisor
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P: 6,236
Quote Quote by kaotak View Post
Where are the positive and negative terminals on our power outlets? [ ... ]
Electromagnetism makes no sense.
You've discovered a super hoax actually, but keep it quiet because there's a whole big industry living off its spread. You don't need two outlets on a power outlet, that's just to increase its price. One single outlet is quite sufficient, as long as you do a rain dance when you switch on your appliance of choice.

BTW, yes, I'm making (gently) some fun of your statements
Kison
#6
Apr22-07, 02:40 PM
P: 7
Voltage is another word for potential difference.

Imagine a D-sized battery. You have the positive and negative side.

Voltage describes the potential difference between the positive and negative side. This relates to the electric field & Coulomb's Law. Basically, the positive side of the battery has an unbalanced proportion of protons & electrons, and thus, when you connect a wire from the positive end to the negative, it is theorized that protons move from the positive side to the negative side. This is called electric current. However, it has been realized to be incorrect, although calculations may still be useful today.

In reality, however, electrons move from the negative side to the positive side. This idea is known as the electric flow.

So the more the voltage/potential difference, the more the positive side of the battery is unbalanced between protons/electrons in comparison to the negative side. So when you connect them with a wire, more charges will flow through the circuit every second.
TuviaDaCat
#7
Apr22-07, 04:52 PM
P: 118
Quote Quote by vanesch View Post
You've discovered a super hoax actually, but keep it quiet because there's a whole big industry living off its spread. You don't need two outlets on a power outlet, that's just to increase its price. One single outlet is quite sufficient, as long as you do a rain dance when you switch on your appliance of choice.

BTW, yes, I'm making (gently) some fun of your statements
its all theft i tell you! every electron i get from the power station i give one back to them, so what the hell am i paying for?!
Xezlec
#8
Apr26-07, 12:32 AM
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P: 308
I like Kison's answer. But let me throw in another one. Think of the electrons in a metal as a sort of "gas" of electrons. They are free to move around in the metal, and they repel one another. If you pack more electrons into the same volume of metal, then they have a higher "pressure" because they are all repelling one another. Conversely, if you suck some electrons out, you have a "vacuum" of electrons, because the positively charged nuclei are "trying to attract more electrons". Sort of.

Now what if you build a "pump" that pumps electrons from one piece of metal to another? Well then you have a pressure that builds in one piece of metal and a vacuum that builds in the other. The vaccum piece is said to have a higher (more positive) "voltage". The voltage between two terminals is simply the difference in electron pressure between one and the other.

And if you connect some conductive path (wire) between the two, the electrons will zoom from the higher pressure to the lower pressure, through that path. The bigger the pressure difference (voltage), the faster they will whiz through the path. The rate that the electrons zip through that path is called the "current", and is measured in Amperes. So current through a path is proportional to voltage. Want more?
Coto
#9
Apr26-07, 12:57 AM
P: 308
In other words one prong of the plug is +'ve and the other -'ve... and the third round one (american outlet) is the ground.
cesiumfrog
#10
Apr26-07, 01:04 AM
P: 2,050
Quote Quote by Coto View Post
In other words one prong of the plug is +'ve and the other -'ve... and the third round one (american outlet) is the ground.
That's only true for about a hundreth of a second.
Coto
#11
Apr26-07, 01:07 AM
P: 308
ok ok.. AC.. but for simplicities sake. Plus isn't it then 60Hz AC?
Xezlec
#12
Apr26-07, 10:15 PM
Xezlec's Avatar
P: 308
Quote Quote by Coto View Post
ok ok.. AC.. but for simplicities sake. Plus isn't it then 60Hz AC?
In some places it's 50 Hz. Each cycle is one polarity for exactly half the time. That's 1/100 second.
cesiumfrog
#13
Apr26-07, 11:24 PM
P: 2,050
Coto, my statement applies regardless of whether your power grid supplies 50Hz or 60Hz (I presume the US uses the latter, and wonder if it's related to their anti-metric stance). My wording was that good. People these days depend too much on calculators - they pick them up too early (before they've rearranged and properly simplified the algebra) and then hang on to them for too long (trusting the 9 digit precision regardless of lower certainty in initial data). </rant>
Coto
#14
Apr26-07, 11:44 PM
P: 308
Actually what I was implying was AC power versus DC power (in my first statement). The second statement was only questioning the 1/100th of a second, where Xezlec seems to have answered it, but it appears you disagree with his answer.. so I'm confused 0_o, are you disagreeing with my question? with my first statement? or did you mean Xezlec?

Plus, I think you're over generalizing how people plug and chug numbers too often in their calculator.. depends who the person is and what they've studied. Personally I haven't had to deal with a calculator since 2nd year.. we have no choice but to simplify algebraically.. that or we get the answer wrong.
Xezlec
#15
Apr27-07, 11:53 AM
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P: 308
Lively little conversation.

cesiumfrog: 1/120 sec is more than 10% different from 1/100 sec. When people say "about", I sometimes assume they mean within +/- 10% or so. I think it was "about" as reasonable of me to assume you meant specifically 50 Hz as it would have been for me to assume you intended your statement to cover 60 Hz. ;-)

As for calculators, I think whatever is faster is better (I'm an engineer). People who use their calculators earlier in the process almost always get done quicker than people who feel the need to get everything nice and perfect and reduced first. And I don't even reduce algebraically anymore. Waste of time -- my calculator's algebra system is better at reducing than I am, and makes far fewer mistakes!

On tests in school, I used to always get the problems right conceptually, and make errors in the algebra on almost every problem. I recognized this tendency, so I would go over and over and over my work to make sure I didn't screw up, being as careful as possible. But I still made algebra mistakes half the time, just because of all the eye-boggling formulas dancing in front of me (and no, I'm not dyslexic, just clumsy). My TI-82 turned me into an excellent and functional engineer. And I got an even better calc later.

So there. :-)
mr200backstrok
#16
Apr29-07, 12:15 AM
P: 27
Xezlec-

I have been trying to understand volts for the last year. Reading through multitudes of definitions (including one thread for about 45 minutes just now) did not do for me what your description did in about 45 seconds.

one question: do the electrons actually travel faster? or is it just that more of them flow? if the latter is true, how fast do electrons flow?
Xezlec
#17
Apr29-07, 12:06 PM
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P: 308
Quote Quote by mr200backstrok View Post
Xezlec-

I have been trying to understand volts for the last year. Reading through multitudes of definitions (including one thread for about 45 minutes just now) did not do for me what your description did in about 45 seconds.
That's one of the nicest things anyone has ever said to me.

In school I was constantly annoyed by professors and books that explained things using terminology no one could possibly understand unless they were already an expert. I guess I try really hard not to do that myself.

one question: do the electrons actually travel faster? or is it just that more of them flow?
DISCLAIMER: Remember that electrons are really obeying quantum principles, so they aren't really just particles, yadda yadda. But assuming you just want to discuss the subject using the "classical approximation" (pretending that electrons are little charged balls that bounce around, rather than probabilistic wave functions), I'll try to give a reasonable answer. No purchase necessary. Void where prohibited.

That's an interesting question. I would say, sort of both.

Electrons are constantly bouncing into atoms and into each other, so they're always flying around in random directions, even when no current is flowing at all. When no current is flowing, the average velocity over all the electrons is 0. This just means that for every electron heading south, there's probably another one heading north. They all have their own little agendas but it all adds up to nothing. Exactly like Congress.

When a current is flowing, it just means that the electrons are heading in one direction more often than other directions. So they have an "average velocity" in one direction. There's a little more to it than that, but you can probably picture what I'm saying. This average velocity is often called "electron drift velocity" by people with college degrees in stuff.

So, yes, a larger current means that when they go in that direction, the individual electrons are more likely to be physically moving faster. And yes, it also means more of them are likely to be heading in that direction in the first place.

if the latter is true, how fast do electrons flow?
My dad (a biologist, so forgive him) once told me he thought electrons all moved at the same speed, nearly the speed of light. This is totally wrong. The actual speed of individual electrons depends on all kinds of things, mainly temperature and the type of material they are flowing in. They move pretty quick, but most of their speed is wasted flying around in circles and loops and bouncing off of things.

Drift velocities actually turn out to be much slower than you might expect! This site gives a value of 3 inches per hour in a typical 100 Watt light bulb situation! Of course, when you consider how many trillions of electrons are flowing at that rate, you realize it's still a significant amount of current.

This might leave you wondering how the light turns on so fast when you flip the switch. Actually, the electromagnetic wave that transmits the "urge to move" to the electrons throughout the wire does move at nearly the speed of light, even though the electrons themselves move at a ludicrously slow average pace. The details of this can get complicated, and my reply is already too long. I'll just stop here for now.

Check out http://en.wikipedia.org/wiki/Drift_velocity or search for "drift velocity", "electron mobility", "charge carrier density", and things like that online.
Pathway
#18
May5-07, 02:05 PM
P: 15
A simple way to understand voltage is just to look at its units.

1 Volt = 1 Joule / 1 Coulomb.

This means that if there is 1 Volt of potential, that means each Coulumb of charge has 1 Joule of potential energy. So you can think of voltage as telling you each charged particle has a certain potential energy. It's like your voltage tells you the particles are on the top of a hill--you can roll each particle down the hill to convert that potential energy each charged particle has into other forms of energy.


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