What Is a Volt? Explaining Watt & Energy Measurement

[chroot]

I agree whole-heartedly with JohnDubYa.

- Warren

 

[JohnDubYa]

Yes they are equivalent if you let the charges go and see how they accellerate.

But that wasn't my question. During the time they are being pulled apart, are the two energies eqivalent?

They're not equivalent anyway. They both CHANGE by the same amount, but their value is not expected to be the same except at one point in time.

How about the volt is the unit of potential energy when two charges of 1 coulombe each both negative are forced together from a great distance to within one meter.

1. A volt is not a unit of potential energy of any sort. You are describing the joule. And it doesn't even work (even for point charges), since k does not equal 1.

2. The definition should not depend on the polarity of the charges.

 

[rayjohn01]

John you are beginning to sound as dangerous as Mr Chroot -- I can only refer you to any physics text or search yahoo for 'electrostatic volt' there are several definitions of 'volt' but the others are circular referring to more units -- I am trying to keep as close as possible to Meter kilogram second with the required extra of charge. You would not like my own text it's 50 years old and is in emu's and esu's which gets really confusing.
The Joule is a unit of work or energy it is common to both mechanics and electrical, the volt is NOT common because it has to refer to charge. The difference is simple it takes a lot more energy to move a coulomb than it does an electron which is why the volt is such a comparatively large unit it refers to orders of magnitude of electrons.
If you cannot accept that then your arguing with basic definitions not me. Ray
In my example the charge sign is not important if they are the same,if they are different then you have to work to keep them apart --same difference.
The energy point is that whatever they gain in potential can be given up as motion or speed ( kinetic).
I believe it is sometimes simpler to relate the energy to motion you can 'see' that , it's hard to see the 'potential' in fact it's probably that which our difference , it's a little difficult to visualise gravitational potential but you recognize something falling to the ground.
And by the way I have no basic objection to analogies they can clearly be useful, Acoustical problems can often be modeled in electronic form the equations can be similar , but here they make exact anlaogies in mathematical form not just loose ones.
If I'm unsure of a quantity and it's meaning I will look up my physics book which deals with dimensional analysis -- that's not a topic for here but this always reduces units to the fundamental ones i.e. MKS with a fourth thrown in where necessary such as here -- charge.

 

[chroot]

rayjohn01,

Once again, I side with JohnDubYa. When you post statements like "the volt is the unit of potential energy..." you lose a lot of credibility here. You seem to really enjoying arguing for the sake of arguing. I'd like to see that stop. Some very accurate and very simple definitions of the volt have already been provided.

- Warren

 

[HallsofIvy]

rayjohn01,

Once again, I side with JohnDubYa. When you post statements like "the volt is the unit of potential energy..." you lose a lot of credibility here. You seem to really enjoying arguing for the sake of arguing. I'd like to see that stop. Some very accurate and very simple definitions of the volt have already been provided.

- Warren

Really?:
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.
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; equivalent to the potential difference across a resistance of 1 ohm
when 1 ampere of current flows through it
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;

I recall a textbook stating that a "volt" is commonly referred to as a "unit of electromagnetic force" but immediately pointing out that the term "Force" is misleading- that the "force" is more correctly a potential energy.

 

[rayjohn01]

Thank you Halls of, for a good accurate and explanatory source DL
try www.plus2physics.com/electrostatics[/URL]
That is a statement not argument .

 

[chroot]

Halls:

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

- Warren

 

[JohnDubYa]

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]

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]

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]

Am I on Candid Camera??

 

[rayjohn01]

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]

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]

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]

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]

Water analogy...Yeah, that's it.

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 amount of water used (the bucket).

["You got to walk before you can run", wisdom from my parents]

 

[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

 

[rayjohn01]

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) -- that's 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 textbook definition is a hypothetical mesurement on a test mass it is identical in form to the electrical case.
If we cannot agree let's call it quits since it not getting either of us anywhere. Regards Ray.

 

[Metallicbeing]

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]

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]

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]

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]

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) -- that's 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.

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 let's call it quits since it not getting either of us anywhere.

It isn't that we differ in opinion. You are simply wrong.