What Is a Volt? Explaining Watt & Energy Measurement

[bayan]

what is a "volt"?

hi to all friends.

what is a "volt"?

can you pl explain the meaning of that word and also "watt" (i know it is used to mesuare the amount of energy but that is about all)

 

[chroot]

There are many ways to define a volt:

A volt is the potential difference that will cause 1 ampere of current to flow through a 1 ohm resistance.

A volt is the potential difference across a conducting material which 1 ampere of current dissipates 1 watt of power.

The potential 1.43 nanometers from a proton is 1 volt.

- Warren

 

[chroot]

A watt is a power dissipation of one joule per second. It's also one volt-ampere.

- Warren

 

[JohnDubYa]

A volt is a measure of potential between two points. A one-coulomb charge will undergo a net change of one joule of energy if it moves from one point to the other.

 

[bayan]

i now understan watt but not volt really.

can you please put it in more simple way. i don't really understand what an ampeer is.

 

[chroot]

Every electron carries a specific charge. A coulomb of charge is the total amount of charge carried by $6.25 \cdot 10^{18}$ electrons. An ampere is this number of electrons flowing past a given point in a wire every second.

- Warren

 

[bayan]

so! ampere is like bandwidth

and

volt is the amount of energy!

 

[russ_watters]

so! ampere is like bandwidth

and

volt is the amount of energy!

No. Volts are an electrical force and coulombs are like mass. So, similar to Newtonian physics, power is force times distance per unit time - or volts times amps. Energy is power (volts times amps) times time.

 

[JohnDubYa]

No, volts are not forces.

What exactly is hard to understand using the definition I posted? Seems clear to me. I hope it's clear to most everyone else.

 

[robphy]

No. Volts are an electrical force and coulombs are like mass. So, similar to Newtonian physics, power is force times distance per unit time - or volts times amps. Energy is power (volts times amps) times time.

I believe the correct analogy is that "charge [displaced]" (measured in Coulombs) is analogous to a [generalized]-displacement... not mass.
Then, "voltage" [akin to an electromotive-force] (measured in Joules/Coulomb) is analogous to a generalized-force, in the Lagrangian spirit. "Current" is analogous to a generalized-velocity. By the way, "Inductance" is analogous to mass.

For the beginning student, this is certainly too advanced to be properly appreciated unless the analogies are carefully presented in an appropriate example.

 

[bayan]

im in year 11 and no background in Electricity what so ever. so can you plaese explain from start?

 

[bayan]

Every electron carries a specific charge. A coulomb of charge is the total amount of charge carried by $6.25 \cdot 10^{18}$ electrons. An ampere is this number of electrons flowing past a given point in a wire every second.

Does this mean that 1 ampere will allow $6.25 \cdot 10^{18}$ electronsto pass in a second at any given point?

if that is the case will a 2 ampere wire alow twice $6.25 \cdot 10^{18}$ electronsto pass in a second at any given point ($12.5\cdot 10^{36}$)

 

[chroot]

Yes, bayan, that's correct. A current of one ampere is defined as 6.25 * 10¹⁸ electrons per second passing a given point in the wire.

I should note that there is no such thing as a "2 ampere wire" -- wires will carry however much current is dictated by the potential applied across them and their inherent resistivity -- at least until they melt.

- Warren

 

[bayan]

i have another question.

1 ohm resistance is potential difference of one "VOLT" produces a current of one "ampere".

does this mean that a 8 ohm resistance is the potential diffrence of 8 "VOLTs" produces a current of one "ampere".

or

does it mean that a 8 ohm resistance is the potential diffrence of 8 "VOLTs" produces a current of 8 "ampere". (although i think this is wrong)

 

[selfAdjoint]

The formula is Ohm's law, E = IR, where E is in volts, I is in amperes and R is in ohms. So you can work out the answers to your questions from that.

 

[krab]

if that is the case will a 2 ampere wire alow twice $6.25 \cdot 10^{18}$ electronsto pass in a second at any given point ($12.5\cdot 10^{36}$)

Looks to me like you do not understand exponential notation. twice $6.25 \cdot 10^{18}$ is $12.5\cdot 10^{18}$, not $12.5\cdot 10^{36}$.
This is vital, so study it first.

 

[bayan]

thanx to all how answered. i think that i understand it now

 

[Janus]

A watt is a power dissipation of one joule per second. It's also one volt-ampere.

- Warren

One stipulation: a watt equals a volt-ampere in DC circuits or purely resistive AC circuits, but not in AC circuits in which the load is at least partially reactive (contains inductors or capacitors.

In the last case, the volt-ampere is a measure of "apparent power". To get "true" power (watts) you have to multiply the apparent power by the 'power factor' which is equal to the cosine of the angle of the phase shift between voltage and current due to the impedance (the combined effect of resistance and reactance) of the circuit.

 

[chroot]

Yes, yes, Janus, but you need to crawl before you can compete in triathlons.

- Warren

 

[DL]

And, on that note, I'd like to ask a question I've been wondering about for a while.

In my grade 9 Science class, the textbook/teacher explained that a "volt" was a measure of how much power each electron was carrying. So a 9-volt battery simply meant that each individual electron coming out of that battery would have 9 "volts" of energy.

I'd been reading quite a bit ahead of myself in physics, and noticed that a unit being tossed around a lot was the "electron volt." So I asked my father, who has a Ph.D in Chemistry, what the difference was between an electron volt and a volt.

He said that an electron volt was the amount of energy each individual electron carried in a current, while a volt was a measure of the total amount of energy in a current. So my school textbook claims that a volt is a measure of energy per electron, and my father claims that a volt is a measure of total energy (adding all the electrons together).

So who's correct? My father is pretty out of the loop as far as chemistry goes, so he could well be wrong, but I wouldn't expect him to be on a seemingly basic issue like this.

 

[Tyger]

And, on that note, I'd like to ask a question I've been wondering about for a while.

In my grade 9 Science class, the textbook/teacher explained that a "volt" was a measure of how much power each electron was carrying. So a 9-volt battery simply meant that each individual electron coming out of that battery would have 9 "volts" of energy.

I'd been reading quite a bit ahead of myself in physics, and noticed that a unit being tossed around a lot was the "electron volt." So I asked my father, who has a Ph.D in Chemistry, what the difference was between an electron volt and a volt.

He said that an electron volt was the amount of energy each individual electron carried in a current, while a volt was a measure of the total amount of energy in a current. So my school textbook claims that a volt is a measure of energy per electron, and my father claims that a volt is a measure of total energy (adding all the electrons together).

So who's correct? My father is pretty out of the loop as far as chemistry goes, so he could well be wrong, but I wouldn't expect him to be on a seemingly basic issue like this.

Voltage is a measure of the electical potential between two points. If there is one volt between two points, and one electron moves from one point to the other, it gains or loses one electron volt of kinetic energy.

 

[JohnDubYa]

RE: "In my grade 9 Science class, the textbook/teacher explained that a "volt" was a measure of how much power each electron was carrying."

Ugh. Not even close.

Objects do not possesses voltage, because the volt is a property of SPACE.

Think of the term "elevation." An elevation of 1 meter above the ground exists regardless of whether or not an object is located at this elevation. Elevation is a property of space. (No general relativity, please.)

Voltage is the potential difference between two points in space. It tells you how much potential energy would be gained or lost if a charged particle moved from the one point in space to the other.

The particle itself does not possesses the voltage.

So if two points in space have a voltage of 1 volt, then a 1-coulomb charge would gain or lose 1 joule of potential energy if it moved from one point to the other (depending on which point had the higher potential).

Any definition of voltage that assigns the term to the particle is incorrect.

RE: "Voltage is a measure of the electical potential between two points. If there is one volt between two points, and one electron moves from one point to the other, it gains or loses one electron volt of kinetic energy."

Potential difference is directly related to the potential energy, not kinetic energy. Otherwise the electrons in a circuit would not move at a constant drift velocity, but would accelerate uniformly, as if the circuit had no resistance.

 

[DL]

So if I'm understanding this... a volt is a measure of the DIFFERENCE in energy between one point and another (the difference between the "altitudes" of two points, to use that analogy). And an electron volt is a measure of the amount of energy an electron has (how "high" the electron is).

Is that remotely close?

 

[rayjohn01]

----

If I can read my physics book correctly the definition of a volt by units is
volts per meter = force per unit charge where force has the normal meaning causing accelleration , but charge has to be defined in some way ( now I guess by the electron) so I'm leaving out any scaling constant .
If you rearrange that it says volt = f.L / q now force x distance = work
so I guess it's work per unit charge or energy per unit charge.
So whoever said it was force does not seem correct.
It is of no importance what type of energy this is ,potental or kinetic the charge either accellerated or was pushed against the potential it's equivalent.

 

[JohnDubYa]

RE: "So if I'm understanding this... a volt is a measure of the DIFFERENCE in energy between one point and another (the difference between the "altitudes" of two points, to use that analogy). "

No, points in space do not have energy, and voltage is not energy. (At least, not in a classical sense.) Instead, a volt indicates how much difference in potential energy a particle would have if it moved between the two points.

Here is an analogy that might help.

Think of a coke can that has a label of 16 fluid ounces. The can itself does not have 16 fluid ounces, and mass is not the same as volume. Instead, the label signifies the mass of coke that would be in the can IF THE CAN WAS FILLED.

Here, fluid ounces is analagous to voltage, and mas is analagous to energy.

If I can read my physics book correctly the definition of a volt by units is
volts per meter = force per unit charge where force has the normal meaning causing accelleration

While true, this is not a helpful definition.

 

[rayjohn01]

Well you have your view , and you like to think of coke cans more power to you
in my view these analogies are rarely accurate -- already in this post voltage has been referred to as 'force' 'energy' etc. which are simply wrong . I see no point in misleading people just because they may lack a little familiarity with the terms, if they are interested they will get there eventually .
It's just the same with the post which said kinetic energy is NOT relevant only potential , it's simply incorrect and omit's the idea that the parts can accellerate -- not an outlandish idea or that difficult to understand.
I continually get the impression that people are talking down to students -- obviously I have no wish to confuse , but innaccuracy does not help.
Ray

 

[JohnDubYa]

Well you have your view , and you like to think of coke cans more power to you
in my view these analogies are rarely accurate

So what is inaccurate about my analogy? The point was to illustrate the difference between a property of space and a property of an object, which I think the analogy does fairly well.

I agree that using analogies is inherently problematic, which is why I only use them once I see that an idea is not coming across.

Your definition, on the other hand, is not only unhelpful but very misleading:

If you rearrange that it says volt = f.L / q now force x distance = work
so I guess it's work per unit charge or energy per unit charge.

A voltage is the potential DIFFERNCE between two points, and indicates the potential energy change for a charged particle between those two points. To call it "the energy per unit charge" is vague and meaningless. The energy of what, placed where, under what conditions? And what kind of energy? The work done by what force?

I'm sorry, but I just don't see where your definitions have been any better than the others. Simply taking a unit and expressing it in terms of other units is no way to describe it. Where's the intuition? The understanding?

 

[rayjohn01]

I'm sorry john but it's not My definition it is THE definition of potential difference = energy per unit charge either potential or kinetic according to what you are doing. Pulling two unlike charges apart gives them potential, letting them accellerate in the field gives them kinetic -- these two are energy equivalent.
The electron volt is Energy because you are considering One electron
(per unit charge)
but the volts units in general are Joules per coulomb. Look it up you don't have to take my word for it.

 

[JohnDubYa]

I'm sorry john but it's not My definition it is THE definition of potential difference = energy per unit charge either potential or kinetic according to what you are doing.

What is your source for this definition?

Pulling two unlike charges apart gives them potential [energy], letting them accellerate in the field gives them kinetic -- these two are energy equivalent.

During the time you are pulling the two charges apart, is the potential energy equivalent to the kinetic energy? Hmmmm?

but the volts units in general are Joules per coulomb. Look it up you don't have to take my word for it.

That is one way to define the volt, but it is a poor definition to use pedagogically. After all, the student could then ask "what is a joule" and be told that "a joule is a volt-coulomb."

Such definitions can go round, and round, and round. And they provide no physics intution whatsoever. Instead, we should define units in terms of physics, not merely other units.

 

[rayjohn01]

To John
Yes they are equivalent if you let the charges go and see how they accellerate.
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.
Of course you could ask what's a meter.
Or to avoid the coulomb 1 eV is the same for two electrons.
Then you can covert by stating the number of electrons in one coulomb.

 

[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.