Understanding voltage



Unfortunately sometimes it does.
Early versions of one popular M68K based machine (I forget which) had a bug that was helped by moving the mouse which generated extra interruots and sped things up.
Bye. Jasen
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wrote:

As was stated earlier... your assessments here are worth exactly squat!
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----------------------------

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Actually, Salmon Egg knows more about electricity than most contributing to
this group. Do you have a problem with that?
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Don Kelly wrote:

Don't feed the dimbulb troll
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aioe.org, Goggle Groups, and Web TV users must request to be white
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On Fri, 03 Oct 2008 09:58:25 -0400, "Michael A. Terrell"

I did not respond to his stupidity, idiot. I will, however, point out yours.
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On Mon, 29 Sep 2008 11:57:18 -0700 (PDT), Rose

OK, Rose, explain voltage to us.
John
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Note that everything you have learned about gravity can almost be directly applied to electricity. In fact the governing equations of EM are almost exactly the same as that of gravity if you could "remove" the polarity aspect. (but the consequences can be dramatically different)
Electrons have attraction and repulsion while "matter" has only attraction.
What causet he attraction/repulsion? It is a force. Gravity on one hand and the electrostatic force on the other.
What about potential energy? Same thing holds for charge. If you take two charges and bring them close together they will have some sort of potential energy... they will either attract or repell and that potential will be converted into kinetic energy just as in mechanics.
Now voltage is a measure of that attraction.
How do you know something has potential energy? You have to let act out on it. (there is no other way except through analysis but that came about from observation.
Voltage, or the electric potential(vs the mechanical potential) is a really a difference in potential energy.
So suppose we have +Q C at (-1, 0) and -Q C at (1, 0), they will attract each other and have forces on them. this would be simiar case to M kg and M kg but the magnitudes of hte forces would be different.
This attraction gives rise to a potential and the potential difference is precisely the voltage. (in the right units for charge)
People tend to speak of voltage as if it were a force(such as electromotive force which has the same units as voltage) but it is not a force just as mechanical potential isn't a force... but it can be used to create a force.
You hopefully know that the gravitational force can have an associated potential with it(the mechanical potential). The same is done with the electric force. Since the forces are conservative we know by mathematics that there is a scalar field who's gradient is the force. It's much easier to work with a scalar field and it's called the potential.
In any case thats more theoretical.
What does it mean in practice?
If someone says that they have a capacitor with 10V "across" it what do they mean? It means they can do some work... and if they were smart they could compute just how much work. All you need ot know is that if there is a potential difference between two points, any two points, and you stick a wire at those two points(a conductor) then current will flow. If you have a lightbulb or led in series with that wire then it might light up... or you might be able to turn a wire.
The mere fact that there is a potential difference implies that you can do work and vice versa. (they are identical concepts as force but viewed from a different perspective)
It doesn't tell you have much work you can do and infact you might not be able to do any depending on the circumstances... but at least in theory you can do some work.
It also is related to current... because current flowing means there is a potential difference. (but not vice versa)
Analogy: A book on a table. The table is a resistance to the book "flowing" down to the ground. The book has potential due only to it's position w.r.t to the earth. If you remove the table the book will convert the potential(voltage) into kinetic energy(think of current) and when it hits the ground or something inbetween it would apply a force that can continue to do work on other things.
There is nothing special about voltage... it's just what we call the potential for electricity. If you understand the gravitational potential then you shouldn't have any problem if you just realize that the basic quanitities one is dealing with are analogous. current = mass flow, voltage = mechanical potential, force = force, electric field = gravitational field, etc..
What's more important is that you have some concept of magnitude of voltage... what is 10V? what is 1000V? Also helps to know something about current and what is 1A vs 100A, etc...
By having that kinda knowledge you'll have a better working understanding. It's similar to mass and energy. Everyone knows what 100lbs is about... or maybe even 1000lbs but most people don't know much about energy. Most people have a better concept of power than energy as they know their lightbulb is using maybe 100W. They still don't really have any clue what it means but they do know it is doing something(i.e. work).
And that's all this boils down too... voltage is a measure of work! Work is what is important! mass is useless if it can't do any work! current is useless if it can't do any work!! Current is a measure of charge in motion... which is usefull to determine how much work it can do.
So ultimately in all the things we are trying to do is to simply things to determine how much work something can do... by knowing that we know how much less work we have to do. But of course we can't always measure work directly... we don't have a special machine that we can ask how much work x is doing and it tells us. We have to break the problem down and learn how to measure it which involves measuring bits and pieces.
(I don't mean to sound dramatic about it but the fundamentals of physics is concerned with it)
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Nice job. Now he can go into fourth year. No wonder our bridges are falling down.
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...

When did one have to understand electricity to understand how to build a bridge?
I'd rather the guy know squat about electricity and be a great bridge builder than build shitty ass bridges cause he spent to much time trying to learn about electricity for some school requirements to "broaden his horizons". He could have spent that time more wisely.
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Jon snipped-for-privacy@Hotmail.com says...

Mechanical engineers don't build bridges either. They do build automobiles and robots, though. Basic electricity would seem to be a useful thing for MEs. Basic physics is rather useful, and required, for EEs. MEs don't have to take the EM semester of physics?

Try a civil engineer if you want a bridge built. I'd rather my civil engineer had the full load of physics too. We *are* talking about basic electricity here.
--
Keith

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says...

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.
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Jon snipped-for-privacy@Hotmail.com says...

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

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says...

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.
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Jon snipped-for-privacy@Hotmail.com says...

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

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says...

You are making a lot of assumptions here from one small post about one thing... You should be ashamed of yourself.
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Jon snipped-for-privacy@Hotmail.com says...

Why? He's a third year engineering student that has zero clue about a rather important aspect of physics that he *SHOULD* have covered. It is the equivalent of my not knowing what mechanical force was when I was a college junior. Somebody failed miserably here.
--
Keith

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Not even anything about the interface between the blade and the ice and
how the blade was ground?
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Congrats.. Somebody got it right. Why didn't someone tell him to understand Ohm's law?
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----------------------------
wrote:

Congrats.. Somebody got it right. Why didn't someone tell him to understand Ohm's law? ---------------------- But it isn't right and saying it is right doesn't help.
--

Don Kelly snipped-for-privacy@shawcross.ca
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You must have missed where he DID mention velocity.
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