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What is a volt ?

by bayan
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chroot
#37
Jul17-04, 11:47 PM
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Halls:

Uh... "potential" and "potential energy" mean quite different things.

- Warren
JohnDubYa
#38
Jul18-04, 02:10 AM
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Warren is correct. Some of you are providing definitions that confuse the two terms.

As for the definition Halls provided:

From “google answers”: Volt: The unit of electrical potential. One volt is the electrical potential that
will cause one ampere of current to flow through one ohm of resistance.
Not a bad definition if the term "difference" was inserted after "potential."

From “Webster’s Dictionary”: Noun 1. volt - a unit of potential equal to the potential difference
between two points on a conductor carrying a current of 1 ampere when the power dissipated
between the two points is 1 watt;
A bad definition, since the language assumes that charge must flow in order for the potential difference to be defined. No, the charge in question (not the charge creating the potential difference) does not even have to exist in order for the potential difference to be defined.

... equivalent to the potential difference across a resistance of 1 ohm
when 1 ampere of current flows through it
Same problem. No charge has to flow in order for the volt to be defined.

volt - a unit of potential equal to the potential difference between two points on a conductor carrying
a current of 1 ampere when the power dissipated between the two points is 1 watt;
Same problem.

Just because it is in print doesn't make it true. (The same applies to my statements, of course, but I think most physicists would agree with me.)

Some of you are simply repeating what you heard. First, make sure that what you heard was correct.
JohnDubYa
#39
Jul18-04, 02:57 AM
P: 1,322
By the way, any definition of volt that relies on the definition of the Coulomb is impractical unless current is taught before the potential. Therefore, I like my definition more.
rayjohn01
#40
Jul18-04, 03:38 AM
P: 284
To John using the accepted resistive definition , a resistor causes power loss into heat
it does so at the rate P = (I^2).R = (energy/sec)
But V = I.R = I. (energy/sec)/I^2 = (energy/sec)/I = energy/Q joules/coulomb
Try Yahoo at the site suggested.
Potential ( electrical) cannot be defined without charge !
JohnDubYa
#41
Jul18-04, 04:12 AM
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Am I on Candid Camera?!?!
rayjohn01
#42
Jul18-04, 05:05 AM
P: 284
To use a mechanical analogue Gravitational potential is given by
workdone( energy ) per unit mass.
In both cases the word potential has been abreviated ( leaving out it's origin ) which the work done by a TEST object ( mass in above) approaching the one in question.
Having defined the energy required for that point the test mass is mentally removed leaving an isolated body with apparent potential -- but the units are defined.
I totally concur that a current is not required but the concept of the test mass IS.
JohnDubYa
#43
Jul18-04, 06:03 AM
P: 1,322
Your gravitational potential definition is no better than your electric potential definition.

So let me get this straight. Suppose we have the Earth. Now we place a test mass (say) 100 meters above the surface of the Earth and drop it. Are you seriously suggesting that the amount of potential at a height 100 meters above the surface of the Earth depends on the amount of work done by the test mass on the Earth? Criminy, that has to be an incredibly smalll number since the Earth barely moves at all if the test mass is dropped. It's not even measurable.

Are you a physicist?
rayjohn01
#44
Jul18-04, 12:04 PM
P: 284
John it's sunday I do not wish to argue - the test mass is taken from the point of interest to infinity read any standard text on the definition of the missleading term 'gravitational potential'. Ray Have a good day.
JohnDubYa
#45
Jul18-04, 02:45 PM
P: 1,322
It doesn't matter. The work done on the Earth by the test mass is completely unrelated to the value of the potential due to the Earth. You are simply wrong.

And if you are still unsure why, consider this. Suppose some entity was holding the Earth in place, not allowing it to move at all. Then the work done on the Earth by the test mass would be 0, no matter where you stopped the test mass. So in this situation the Earth would have zero gravitational potential at all points in space. But that is insane, because masses are still gravitationally attracted to the Earth.

It is clear that you are not a physicist. Am I correct?
Metallicbeing
#46
Jul18-04, 03:10 PM
P: 69
I have a simple water analogy that I use to help new apprentices.

Say you have a water-hose that's filling up a bucket.

- Voltage can be characterized as the pressure moving the water.

- Amperes (Amps) can be characterized by the volume of water passing a given point within a given time.

- Watts can be characterized by the total amout of water used (the bucket).

["You gotta walk before you can run", wisdom from my parents]
chroot
#47
Jul18-04, 03:24 PM
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Metallic,

Your analogy with power is simply wrong... power is the rate of expenditure of energy, not the amount of water (charge) that has already flowed through a pipe (wire).

- Warren
rayjohn01
#48
Jul18-04, 03:30 PM
P: 284
To John ,you are telling me that no work is done on a mass which falls from your hand to the earth ( kinetic) and that no work is done by lifting it from the ground upward (potential) -- thats nonsense and you know it. all you have to do is think of the energy required to launch a space rocket and imagine it does not stop till very far away. ( what in heck did they need fuel for ??
THAT is the definition of 'gravitational potential" it's the work done /rocket. in rocket units from the start point.
I took university physics for 4 years with electrical and electronic engineering and I'm afraid your intuitive idea of what potential stands for is in error. Not only that but you cannot define how to measure it.
The text book definition is a hypothetical mesurement on a test mass it is identical in form to the electrical case.
If we cannot agree lets call it quits since it not getting either of us anywhere. Regards Ray.
Metallicbeing
#49
Jul18-04, 03:41 PM
P: 69
Quote Quote by chroot
Metallic,

Your analogy with power is simply wrong... power is the rate of expenditure of energy, not the amount of water (charge) that has already flowed through a pipe (wire).

- Warren
Watts are "Static"

Watt/hrs. are "Rate"

I meant that "the bucket" symbolizes total power used in an instance of time.
chroot
#50
Jul18-04, 03:44 PM
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Quote Quote by Metallicbeing
Watts are "Static"

Watt/hrs. are "Rate"
Absolutely incorrect.

1 watt = 1 joule per second, where the joule is a unit of energy.

The "watt per hour" is, shall we say, a unit you don't come across often unless the power in some circuit is changing.

You may be confusing your terms with the watt-hour (NOT watt/hour) which is the energy delivered by one watt of power over 3600 seconds, or 3600 joules.

- Warren
chroot
#51
Jul18-04, 03:46 PM
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JohnDubYa,

Are you simply trying to impress upon rayjohn01 that the value of the potential is arbitrary (since you are free to select your zero anywhere you like) and only differences in potential matter?

rayjohn,

It should be clear that many people here have quite a bit more education in physics than what you got for your BSEE.

- Warren
Metallicbeing
#52
Jul18-04, 03:55 PM
P: 69
Quote Quote by chroot
Absolutely incorrect.

1 watt = 1 joule per second, where the joule is a unit of energy.

The "watt per hour" is, shall we say, a unit you don't come across often unless the power in some circuit is changing.

You may be confusing your terms with the watt-hour (NOT watt/hour) which is the energy delivered by one watt of power over 3600 seconds, or 3600 joules.

- Warren
O.K. The bucket analogy sucks...
JohnDubYa
#53
Jul18-04, 04:09 PM
P: 1,322
To John ,you are telling me that no work is done on a mass which falls from your hand to the earth ( kinetic) and that no work is done by lifting it from the ground upward (potential) -- thats nonsense and you know it.

The work done on WHAT???

Here is what you posted earlier.

In both cases the word potential has been abreviated ( leaving out it's origin ) which the work done by a TEST object ( mass in above) approaching the one in question.
"...the work done by a test object. On what? The Earth? If so, I have illustrated why this definition is absurd. If the work is being done by the test object, upon which body is the test object performing work on? You have yet to answer the question.

[quote]
I took university physics for 4 years with electrical and electronic engineering and I'm afraid your intuitive idea of what potential stands for is in error. Not only that but you cannot define how to measure it.[/b]

Well, with t-h-o-s-e credentials how could I possibly disagree? I mean, what would I know in comparison to someone who has had four years of electrical engineering?

If we cannot agree lets call it quits since it not getting either of us anywhere.
It isn't that we differ in opinion. You are simply wrong.


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