Difference between Voltage and Current

[charlie b]

Some or all my opinions might change later. But for right now none have changed.

That is certainly your privilege.

Charlie makes a very good argument and it?s hard not to agree with him.

I would agree with that. :happyyes:

The opinions I give are my own, I don't expect anyone to agree with them, all I ask is for you to think about them and give me your honest opinion.

I hope you understand that I was not expressing an opinion, but rather providing fact. I was explaining the physics of the situation, in what I intended to be non-technical terms.

The way Charlie explained it the voltage is a separate material thing that flows in the conductor and governs what the current does. I am very skeptical about that.

You should be skeptical, since that is not what I said. :happysad: Voltage is a not ?material,? in that it has no mass, no weight, and no ability to move from one place to another. Voltage does not ?flow? in a conductor, but it does call current into being. Voltage is the reason that charge moves within a conductor, and as I had said it is ?charge in motion? that defines current.

 

[Hv&Lv]

I think the analogy actually holds reasonably well for this. Increase the pressure and the flow will increase in the pipe, all other things being equal. Increase the voltage applied to an electrical and more current will flow.

To a point. At what point will the flow (current) have to change inversely to the pressure (voltage)?

Aren't you supposed to be visiting with your sister? (Hyacinth)

 

[charlie b]

There are also some ways in which that analogy falls short. For example, the units of measure for pressure and voltage are nothing at all like each other.

I think the analogy actually holds reasonably well for this. Increase the pressure and the flow will increase in the pipe, all other things being equal. Increase the voltage applied to an electrical and more current will flow.

Please observe that I was referring to the units of measure of pressure and voltage, not their nature or their impact on flow.

 

[Besoeker]

Please observe that I was referring to the units of measure of pressure and voltage, not their nature or their impact on flow.

Of course they are different. That's why it's an analogy.

 

[ronaldrc]

Charles sorry I didn't mean to miss quote you.

I think in most ways it is a good analogy to water flowing.

I think the main place that the water analogy falls short or just does not apply in the least is when
discussing induction there is no comparision what so ever.

 

[Besoeker]

Voltage is a not ?material,? in that it has no mass, no weight, and no ability to move from one place to another.

You could say the same about pressure.

 

[Besoeker]

To a point. At what point will the flow (current) have to change inversely to the pressure (voltage)?

When you get a discontinuity

Aren't you supposed to be visiting with your sister? (Hyacinth)

She's visiting us for the weekend.
Jolly inconsiderate given that it's the last race of the F1 2011 season!
Sebastian Vettel has done an amazing job having already clinched the title. Not only that, he has taken a number of records on the way to that title.
A talent that may well eclipse his elder compatriot, Michael Schumacher, in every department.
A back to back double world champion at the highest level in the sport - and still aged just 24.

 

[Rick Christopherson]

I think a better analogy for understanding voltage is a gravity-driven hose instead of a pump-driven hose. The height of each end of the hose represents the potential energy of each end respectively. If both ends of the hose are at the same height, then there is no difference in potential energy and no water will flow. No matter how high or low both ends are moved, if they are still at equal heights, there is no difference in their potential energy, and no water will flow.

The higher you elevate one end with respect to the other end, the greater the difference in potential, and the faster the water will flow.

Turbulence was mentioned (forgive me, was this by Charlie?). This is still applicable, and it is equivalent to the resistance of the wire. Electrons also experience a vary similar turbulence in anything other than superconductors. Even though the average electron speed is moving down the length of the conductor, the actual electron path is very erratic and includes moving in a rather "turbulent" fashion.

Oh, I believe there was also some mention about there not being an equivalent "density" for electrons. That is not correct, and we use the molar density of the charge to determine the actual speed of the electrons. When it was mentioned previously that electrons only "wiggle" a little bit in an AC circuit, the following Wiki page is what I pulled up as a quick reference instead of diving back to my ancient text books. http://en.wikipedia.org/wiki/Drift_velocity I didn't really read the Wiki page, but just glanced at it.

There are analogies for capacitors and inductors with hydraulic systems. It's been a while, but I think the analogy for a capacitor is a diaphragm across a pipe or tank, and energy is stored in the elasticity of the diaphragm. Oh, while looking up what the inductor analogy might be, I stumbled across this Wiki page that describes them all. http://en.wikipedia.org/wiki/Hydraulic_analogy

One of the things that we sometimes take for granted while working with our simplified electrical equations is that they are rooted in the more complex equations in physics of charges and fields. Sometimes, in order to better understand electrical systems, we have to remember to think back to the original principles that led to the derivation of our simplified equations.

 

[Besoeker]

I think a better analogy for understanding voltage is a gravity-driven hose instead of a pump-driven hose. The height of each end of the hose represents the potential energy of each end respectively.

Except that neither pressure or voltage is energy.
Potential or otherwise.

 

[Rick Christopherson]

http://dictionary.reference.com/browse/analogy

 

[Besoeker]

http://dictionary.reference.com/browse/analogy

You seem to have missed the point.
I agree with the pressure and voltage analogy.
From my post #19:

I think the analogy actually holds reasonably well for this. Increase the pressure and the flow will increase in the pipe, all other things being equal. Increase the voltage applied to an electrical and more current will flow.

Maybe you missed that.
My point was that neither pressure or voltage is energy.
Potential or otherwise.

 

[Rick Christopherson]

If it's not energy in some form or another, then how does it cause an electron to move? Wouldn't that constitute performing work for "free"?

 

[Besoeker]

If it's not energy in some form or another, then how does it cause an electron to move? Wouldn't that constitute performing work for "free"?

It misses the other elements.
The Joule, the basic unit for electrical energy, is one Volt times one Amp for one second. A Watt-second if you like.

 

[Rick Christopherson]

I'm running late, so I haven't looked at this very closely, but from Wiki (note the last line):

Because energy is defined via work, the SI unit for energy is the same as the unit of work – the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton-metre and, in terms of SI base units:

An energy unit that is used in atomic physics, particle physics and high energy physics is the electronvolt (eV). One eV is equivalent to 1.60217653?10⁻¹⁹ J.

 

[Besoeker]

I'm running late, so I haven't looked at this very closely, but from Wiki (note the last line):

Because energy is defined via work, the SI unit for energy is the same as the unit of work ? the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton-metre and, in terms of SI base units:

An energy unit that is used in atomic physics, particle physics and high energy physics is the electronvolt (eV). One eV is equivalent to 1.60217653?10⁻¹⁹ J.

Excellent.
Note the very last letter.

 

[Rick Christopherson]

Oh, I get it now. You're nitpicking for the sake of nitpicking. I forgot you have a tendency to do this. Yes, your nitpicking is correct, but the message behind it is not.

A gravity field does not represent a potential energy without a mass to act upon, and an electric field does not constitute a potential energy without a charge to act upon. But that doesn't alter the validity of the analogy because both require the object. In both cases, the object is assumed to exist or we wouldn't be having the discussion.

 

[Besoeker]

Oh, I get it now. You're nitpicking for the sake of nitpicking. .

Not so.
My point was that neither pressure or voltage is energy.
That's a fundamental point.

 

[ronaldrc]

Charlie

Below is the definition of voltage I give and I agree it is a bad choice of words.I give that off the top of my head.

The definition of voltage is the force behind an electrical current or the potential between the two points of an Electrical source. It is an expression or an entity that pushes the current through the conductors or wires. According to that definition it is not a physical thing that flows through the wires with the current.

Your answer

I must report, with respect, that here you have it completely wrong. Although the ?water analogy? would have you thinking of voltage as the ?driving force? for electron flow, voltage is absolutely not about ?force.? The definition of voltage is the amount of energy required to move an amount of charge from one location to another. The unit of measure called ?one volt? is defined as ?one joule (of energy) per coulomb (of charge).? As I said earlier, this is not at all similar to the unit of measure for pressure.

I should have said

The definition of voltage is the force behind an electrical current or the energy potential between the two points of an Electrical source. It is an electrostatic field that pushes the current through the conductors or wires. According to that definition it is not a physical thing that flows through the wires with the current.

I realize that want be exactly the way you would word it but is that close enough?

I realize when we use the water flow as a analogy of electrical current that the weights and measures will not be the same between the two and I don't think any one else would think that either.

In water pumps we use head pressures in PSI as driving force. --It did take energy to create that force.

In the electrical circuits we the term volt as the driving energy.-- I used the word Force.

I don't think I am being unfair to say you strenght this a little to make me look wrong.

Ronald

 

[iceworm]

Ronald -
Here's a novel thought - pitch all of the mechanical analogies in the toilet. Not one is worth a pitcher of warm spit. Well, okay, one analogy - one time. One of the first things taught in a Methods of Instruction class, you need a hook to get from the known to the unknown. Once that is done forget the analogy - It Is Useless. For electrical, water in a hose is fine - it is not true, but it allows one to bring in the relationship between voltage, current, resistance, Ohm's Law. Build on that relationship. The equations that describe electricity are a math model. They are repeatable and allow accurate prediction of an electrical system reaction. Any reference to a mechanical analogy is meaningless and distracting.

For those that feel like they need a mechanical analogy to understand - I truely doubt they do. They beleive in the wind - and they can't see that. "But I can feel the wind." Yeah that's great - stick your finger in a light socket. Bet you can feel that too.:roll:

As for the charge carrying component and current direction, it just doesn't matter. Forget it. The equations that make up the math model are completely independent of any notions. Personally, the concept of liking either electron or comventional flow just doesn't come up. Who cares - the equations don't.

Anybody studying the electrical model past Ohm's Law will need basic algerba and trig. With those one can add impedance, inductance, capacitance, real power, reactive power, power factor, concepts of leading, lagging.

I've watched your posts plenty. You easily have the grasp of all the concepts. One look at a graphic showing the definitions of the voltage across an inductor and the current through an inductor you will understand the concept of Lead/Lag immediately - no question. I'll draw one up and get it scanned - hopefully today.

Ditch the mechanical analogies. They just don't fit. And look at some of the nonsense commens they brought. Let the equations tell you the relationships between the current and voltage across components not some hokey, misfit, mechanical analogy.

As for your comment about "Voltage flowing", you are right on. If you hear it, say, "Uh-huh" and walk away. If it is in a textbook, through it in the garbage.

The Worm

 

[ronaldrc]

Ronald -
Here's a novel thought - pitch all of the mechanical analogies in the toilet. Not one is worth a pitcher of warm spit. Well, okay, one analogy - one time. One of the first things taught in a Methods of Instruction class, you need a hook to get from the known to the unknown. Once that is done forget the analogy - It Is Useless. For electrical, water in a hose is fine - it is not true, but it allows one to bring in the relationship between voltage, current, resistance, Ohm's Law. Build on that relationship. The equations that describe electricity are a math model. They are repeatable and allow accurate prediction of an electrical system reaction. Any reference to a mechanical analogy is meaningless and distracting.

For those that feel like they need a mechanical analogy to understand - I truely doubt they do. They beleive in the wind - and they can't see that. "But I can feel the wind." Yeah that's great - stick your finger in a light socket. Bet you can feel that too.:roll:

As for the charge carrying component and current direction, it just doesn't matter. Forget it. The equations that make up the math model are completely independent of any notions. Personally, the concept of liking either electron or comventional flow just doesn't come up. Who cares - the equations don't.

Anybody studying the electrical model past Ohm's Law will need basic algerba and trig. With those one can add impedance, inductance, capacitance, real power, reactive power, power factor, concepts of leading, lagging.

I've watched your posts plenty. You easily have the grasp of all the concepts. One look at a graphic showing the definitions of the voltage across an inductor and the current through an inductor you will understand the concept of Lead/Lag immediately - no question. I'll draw one up and get it scanned - hopefully today.

Ditch the mechanical analogies. They just don't fit. And look at some of the nonsense commens they brought. Let the equations tell you the relationships between the current and voltage across components not some hokey, misfit, mechanical analogy.

As for your comment about "Voltage flowing", you are right on. If you hear it, say, "Uh-huh" and walk away. If it is in a textbook, through it in the garbage.

The Worm

Ice worm I am fine I have been retired for 2 years. I worked in the trade as an Electrician for 35 years
had a total of 40 years in the trade.

I do not need and havn't needed an analogy for the last 38 years and I did fine.

I think a analogy is fine for a learning tool you can't do everything with math.
I know enough math to get by. I studied math years ago even PF,inductor and capacitance.
And yes I have for gotten all that. I do not need or want to brush up on it.

But I appreciate the offer though. Ronald