Voltage is work (or energy) per unit charge required to move a unit charge from a to b in an electrical field. An electrical field is produced by the presence of other charges. Think of mechanical potential energy per unit mass required to move a unit mass from point a to b in a gravitational field. A gravitational field is produced by other masses.
The two are analogous. In both cases it doesn't matter what path you take from a to b.
-- Don Kelly dhky@shawcross.ca remove the X to answer
Cool. Explain voltage to us.
John
to
So are you trying to say that learning about electricity is not a wise use of time?
OK, Rose, explain voltage to us.
John
So are you trying to say that learning about electricity is not a wise use of time?
-- Of course not... But that you seem to imply that if he doesn\'t know electricity that he can\'t build a good bridge which makes no sense. But for practical reasons not everyone can learn everything or even one person learn everything. Obviously knowing a bit about basic electronics doesn\'t take much time though. Bridge building requires absolutely no knowledge of electricity(theory wise) and even if it did use a bit(say for lighting) it is not fundamental to building bridges and others can handle that.
True... but that is not inherent to bridge building. Bridge building is about choosing the right materials and dealing with the forces which has nothing to do with electricity. Although your point shows that what I said is not completely true.
I'm not saying electricity is useless and I'd rather everyone know much as they can about everything... but if you gotta choose to split of your time or not then it's usually best to not.
Although usually learning the basics doesn't take that long. My point wasn't about learning electricity but about roses statement that implied the guy couldn't build a good bridge if he didn't know about it... which is ridiculous.
Ok... yes, I know that. Alhtough the overlap is much greater. Learning about your statics and dynamics is a major part of ME and CE'.
My response was specifically to the statement by Rose.
True... but again, my statement was specifically about roses statement.
He/She is implying that if you don't know even the basics of electricity then somehow you can't build a good bridge.
What I'm implying is that if the guy is an amazing bridge buildering(Ok, I know he's ME but Rose is the one who brought up the bridge building) then it's ok for him to suck as EE.
I'm sure Tesla sucked at ice hockey but I don't see anyone complaining that he should have spent more time on it. (What does ice hockey have to do with EE? Who knows but thats not the point)
Also we are getting off the point as if the guy is suppose to be the best. There are many EE's that don't even have a good understanding of their own craft so we should get onto those guys first.
Understand. I was debating which one to respond to. ;-)
I don't think you should be an engineer without some knowledge of basic physics. The fundamental units are rather important in all engineering disciplines. I'm surely not an ME, but I know F=MA and you can't push with a rope. ;-)
"Suck as an EE" "sucks at fundamental physics"
Understandable. I didn't learn any ice hockey in college physics either.
The argument wasn't about whether or not there are EEs who shouldn't be, rather whether it's understandable for an ME to lack basic electrical knowledge. Would you think it OK for an EE to not know that F=MA?
-- Keith
The idiot is probably an ObamaTard too.
Minus a good margin to keep things from ever approaching the flash point of paper... at the very least. It is actually held to a temperature even lower than that. The flash point (or melting point_ of PVC is likely lower than that of paper. Why PVC is still in use is beyond me.
First off he's still in school... and second he said he didn't understand voltage... that is only one concept in a huge number of concepts. Also we do not know to what extent he didn't understand.
I can promise you that many EE graduates do not understand voltage but only memorized formulas and defnitions..
So it isn't about what's right or wrong but what is real and not real. Sure I would want everyone to have a little knowledge of everything... but that isn't practical because then end up not being good at one thing
Did you ever stop to think that maybe the reason he didn't understand it was that the professor that he took the class from that taught it didn't do a good job? Do you also realize that there are many levels of understanding it?
It's not that I don't agree with you that he should understand it and I'm not even debating that.
But let me ask you something: Suppose he is the best bridge builder in the world but he doesn't understand voltage... is it "ok"? Can we let it slide or do we have to send the guy back to kindegarten to learn it? What if it just can't do it and totally sucks at it? and he doesn't go around pretending not too but just wants to build bridges... surely it's ok? It's much better than 99% that don't know and don't give a shit about anything?
I think you guys are jumping to to many conclusions about the guy. We do not know his circumstances and shouldn't judge him from one post on usenet that says
"Hey, I'm in 3rd year mechanical engineering and I still don't feel like I have a strong understanding of what voltage is. Maybe someone can help explain the concept."
In fact the question's he asks are quite fair and natural and means he has an inquisitive mind. So instead of judge him we should try to help him understand. As long as he doesn't pretend to know something and long as he doesn't put peoples life at risk then it's not a problem. Sure we can hope he will understand everything the first time and learn everything he can but this isn't a fairy tale.
As was stated earlier... your assessments here are worth exactly squat!
Well... that one at least showed a hint of knowledge.
Ever seen such devices attached to ships?
I kinda forgot to answer your questions:
Since you said you understand current, you do realize that I = Q/t? and that if Q goes up and t goes down in proportion then I doesn't change? The same thing is going on with voltage.
Analogy: If you have 10 N weight lifted up 3 feet then it has the same potential energy as a 5 N weight lifted up 6 feet? (ok, not exactly since the gravitational field is a bit weaker but close enough)
Remember that voltage isn't a fundamental quantity but is a function of more than one.
V = J/C is one expression of V but it's also V = W/A as it is A*Ohm. (we get the last two from ohms law)
I think you really need to think about it more. Take 2 C of charge and place them at some distance apart, say it has 10 joules of energy, if you now move them apart you increase the energy to maybe 20 joules? Or equivalently, but with less information, we have went from 5V to 20V.
It is exactly analogous with many other physical quantities that depend on more than one thing. If I have 80 C moving past a point in 2 second then that is 40A but so is 40 C moving past a point in 1 second. I could also have one electron moving past that point in 1/40C of a second and it would also be equivalent to 40A.
Also if I reduce the time I move the 80C then from 2 seconds to 1 second(if I slow them down) then I cut the current. In fact if I "freeze" everything, even though I have 80C of charge sitting there, I have no current at all!
"The difference in voltage measured when moving from point A to point B is equal to the work which would have to be done, per unit charge, against the electric field to move the charge from A to B. "
Note that it is a "per-unit" quantity that depends only on the distance in the electric field. It doesn't depend on the amount of charge which is why it is being divided out.
Think of it as energy per unit charge. Current gives us the other half of the equation. If we know the energy per unit charge, or the voltage difference, and we know the charge per second(along some path), or the current, then if we multiply them we have
Energy/charge * charge/time = energy/time = power = work/time
i.e., V*I = P
If we had some idea of the time involved we could get the energy too.
If you want a microscopic concept then it is the energy contained per electron in the electric field... (do you understand the electric field?)
The macroscopic concept is one of "force" or some "ability to do work"... note that it is a mixed up concept because it's not fundamentally correct but it is understanding by "consequence". (kinda like understanding anything we have to associate it with things we know)
Just like the electric field is force between charges divided by charge, electric potential (ie, voltage) is potential energy divided by charge.
You aren't having trouble with voltage, though. You are having issues with energy. What is it? Think about that for a bit before continuing...
My answer is that it is the potential to move something. When you hold a hunk of matter above the ground, it has the potential to start accelerating when you let go of it. Thus, it has potential energy, given to it by the attraction of gravity. How much? It depends on how high you hold it.
Same thing for voltage. It is the potential to move charged particles around (ie, create a current).
Just like the attraction of gravity gives a hunk of matter different 'potential energy' at different altitudes above the ground. So, to get the hunk of matter up there, somebody had to give it some energy.
To get 10 volts out of 2 coulombs, you need to put in 20 joules of energy to separate the charges.
Voltage, as used in electronics, is a relative measure. You pick some place in the circuit, and say "that is ground", meaning that is where you measure the rest of the voltages from. Then, take a particle, like an electron, and integrate the force it takes you to move it to some other place in the circuit with respect to distance. Thankfully, it doesn't matter how you go, any path will do. Now, divide by the charge of the particle. That number will equal the voltage at the destination point, relative to the ground of the circuit.
In physics, there are actually two potential fields, the electrostatic potential, and the vector potential. Those fields, the first a scalar field, and the second a vector field, influence how a charge will move. A charge will move along the gradient of the electrostatic field, and a moving charge will turn to align its motion with the vector potential.
Regards, bob monsen
-- Not even anything about the interface between the blade and the ice and how the blade was ground? Pity...
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Congrats.. Somebody got it right. Why didn't someone tell him to understand Ohm's law?
Third year. He's specializing by now.
Irrelevant.
It certainly is *EXPECTED* that a Junior in an engineering college knows the rudiments of physics.
Possible, but irrelevant.
Then what, exactly, are you debating?
He's not the "best bridge builder". He's a college student who apparently slept through physics. No, I don't want him building my bridge.
Yes, by the third year he's supposed to have had at least three semesters of physics, one of which should have been E&M.
Ok, I'm not judging him. His college should be boarded up.
-- Keith
You are making a lot of assumptions here from one small post about one thing... You should be ashamed of yourself.
if you picture current as the rate of flow of water in a pipe, voltage is the water pressure.
in the water analogy: Joules / Cubic meter IOW: pascals
it has it by being displaced by a from where it would like to rest the further it is displaced the higher the voltage.
joules/2
different pressures, with 10kPa you can spin a turbine nicely, but same flow rate with only 10Pa behind can do very little work.
Bye. Jasen
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