Difference between Voltage and Current

[kwired]

I don't think that this is what Ronald had in mind.

Exactly. When using an analogy we are just trying to use something that may be similar but not exactly the same as an example to help understand. That is why we usually say voltage is like the pressure in the water pipe and current is like the flow of water in the water pipe. We don't normally say voltage is the same as pressure in the water pipe or current is the same as the flow of water, because it is not the same. Sometimes what is different about the comparison may even be pointed out to insure it is understood it is not the same, but can still be used as a general comparison to help someone understand what is going on.

People can see or feel the water pressure or the flow of water and can understand that easier than what exactly is happening in an electrical circuit where voltage and current can not be seen and really is not a good idea to feel.

 

[rattus]

Don't you think this discussion way out from the OP's original post?

 

[jjkind]

...Capacitors store energy in an electric field....

Hmmmm....when you make some substitutions into the equation for capacitive energy to describe things in terms of electric field, you have to deal with some non-intuitive variables and units (non-intuitive in this context, at least), like force and Newtons. Nothing wrong with this, but I suggest "capacitors store energy in the form of an electric charge." This allows you to describe things in terms of charge and voltage.

I've been reading a lot about static electricity and trying to figure out the capacitance of something like an irrigation system (the "system" would be the irrigator and the ground). Someone suggested to me a lightning strike could energize the metal portions of the system (could happen) and that the resulting charge could cause a discharge of sufficient magnitude to kill a human (not plausible). I emailed an expert on static electricity and he told me that although a system like this could be charged to 10s of kilovolts, the capacitance of the system would be on the order of 100s of pico-Farads, resulting in a discharge of a fraction of a Joule (and this high voltage would dissipate quickly via corona discharge and current flow to ground through tires, making human contact highly unlikely).

I'm not simply rambling...in the process of thinking about all this I realized that my mechanical analogies for electricity were very limited in explaining all but the simplest of electrical phenomenon, as others here noted. I've started to think of electricity as "transfer of charge" as opposed to "movement of electrons." I find it pretty helpful to think this way, at least for some things (like what happens inside a person when they are electrocuted, where there are positive carriers as well as negative ones).

Perhaps this is useful when thinking about the difference between voltage and current. Current is the movement of the charge carriers to equalize or create additional charge. Voltage then describes the resulting potential state and is useful in its predictive ability to describe how the state will change.

@Rick Christopherson

I agree with your statement regarding electron orbitals. When you start talking about stimulated emission of radiation from electron movement between energy levels in an atom, you're getting into the realm of quantum mechanics and thinking about things in terms of "current" and "voltage" is no longer important. You could describe things in this manner, but it wouldn't be useful, since things are "quantized." In conductors such as aluminum "charge is tranferred" (using analogy suggested above) by free electrons in outer orbitals of the metal (the existance of which makes a metal a metal). When you pass enough current through a small filament you will actually transmit enough energy to the metal itself that the electrons in inner orbitals are excited, jump to different shells, then fall back, causing radiation to be emitted in the visible realm (light).

 

[charlie b]

The definition of voltage is the force . . . .

I would not call that its definition. The effect that voltage has on electrons is that it tends to impose a force upon them, causing them to move. But the definition of voltage is, as I have said before, a measure of the amount of energy it takes to move an amount of charge from one place to another.

It is an electrostatic field that pushes the current through the conductors or wires.

That is true.

. . . it is not a physical thing that flows through the wires with the current.

I am confused. Did anybody disagree with this notion? I did not. It is a physical phenomenon, but it does not ?flow.?

 

[Besoeker]

Charlie


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.

You can have a voltage without current.

 

[charlie b]

Do you know or have you ever studied Apparent voltage

I have never heard of the phrase “apparent voltage.” I am inclined to think that you made it up yourself. I did a quick Internet search, and I found that phrase used in the arena of biophysics and some other sciences, but not in the arena of power systems engineering. In any event, that phrase has nothing to do with anything I intended to convey.

. . . this is what Charlie has been trying to say but he was so hot headed he could not think of the correct term.

I would think that an apology is in order. If you can find some wording in any of my previous posts that gives the impression that I was a hot head, then please tell me where they are. I would not hesitate to apologize, if I have given offense. But I think you are the one who owes me an apology, for the unfounded accusation that I have been a hot head.

What’s the difference between me calling or saying that voltage is the same as pressure or force produced by a water pump, when Charlie wanted to hear the exact term Energy.

The difference is that saying one thing is like another is an analogy, and stating the precise meaning of a word is giving its definition. And voltage is not defined in terms on “the exact term energy,” but rather in terms of both energy and charge.

And Charlie not just saying are you talking about the apparent voltage produced by the inductive kickback or the resulting voltage created by a capacitor after the sine crosses the zero line.

I am not talking about “apparent voltage,” and I do not know what you intend to mean in using that phrase. Also, capacitors do not have voltages created by inductive kick. You have inductance confused with capacitance.

 

[mivey]

You can have a voltage without current.

And current without voltage.

 

[mivey]

If you can find some wording in any of my previous posts that gives the impression that I was a hot head, then please tell me where they are.

FWIW, I saw nothing of the sort in your posts. I think I would remember because I would have found it interesting that you would be getting "hot-headed".

 

[charlie b]

And current without voltage.

Not unless the conductive medium has zero resistance. :happyno:

 

[mivey]

Not unless the conductive medium has zero resistance. :happyno:

Details, details.

 

[mivey]

However, I am not sure this is true when an electron moves from one voltage potential to the next. I don't believe it absorbs or releases energy.

The energy is stored in the surrounding electric field.

 

[ronaldrc]

I have never heard of the phrase ?apparent voltage.? I am inclined to think that you made it up yourself. I did a quick Internet search, and I found that phrase used in the arena of biophysics and some other sciences, but not in the arena of power systems engineering. In any event, that phrase has nothing to do with anything I intended to convey.

Charlie oh buddy, I'm inclined to say you are exactly right on that one. I was thinking about what you said
about the inductor or capacitance generating a voltage and I got to thinking what I had studies years ago.


What I did I confused apparent voltage with apparent power I didn't realize I had it turned around untill someone pointed it out there was not such thing as apparent voltage. Then I also did a internet search and come up empty. Then I knew I had it confused with apparent power, sorry.

But honestly I didn't do it on purpose.

Although I did invent it for another post remember. :roll:

 

[ronaldrc]

No, I missed the invention of apparent power. Is there a definition?<BR><BR>I'm
back to work Monday, so I've only got today and tomorrow.

Ice Worm I think this was the start of the naming of apparent voltage, http://forums.mikeholt.com/showthread.php?t=140910&page=12

Voltage can be a unit, the electron, raised to a great height. Like a rock at the top of a cliff ready to fall the full distance to the ground state, potential energy. Not necessarily more of them pushing each other harder. Pushing involves movement, which would imply current flow. Voltage is the static case. A rock at the top of the cliff that may fall, it has potential energy. The rock falls from positive (greater height), to negative (lesser height). The unit electron has a negative charge and moves from + to -, greater to lesser height.

I like that voltage analogy.

Ronald,
There is no such thing as apparent voltage. Voltage is real. Current is real. However, when you combine these two and they are out of phase, then you end up with real and apparent power due to the displacement of the waveforms. Voltage without a current can do no real work. Likewise, current without a voltage can do no real work. Only when the two exist at the same time can real work be accomplished.

Rick thanks for setting me straight on Apparent Power I remembered wrong.

Ronald, I agree with the water flow analogy. The units don't have to match. However, your definition of voltage might mislead some. I would just say that voltage is analogous to water pressure, and current is analogous to water flow.

As for apparent voltage, a better term is the induced emf, (back emf) which arises from the same mechanism as in a transformer, i.e., a changing magnetic flux. this induced emf is just as real as it is on L1 and L2 in a split phase service.

Apply a battery to an ideal inductor. The battery pushes in one direction, the induced emf pushes in the other. The result is,

i(t) = (V/L)t, a straight line.

It gets a bit more complicated with sine waves.

Thanks for agreeing with me on the water flow analogy.
It gets a lot more complicated that, But remember I was an Electrician all we had to do was make sure it was wired up correctly. I do remember in trade school when we where studying all the math. I wondered where we would ever use all the math that they tried to teach to us? Its all in the pass now. But I do like to discuss theory some times but just like this thread it does get out of hand at times. I know its mostly my fault for being rusty in everything but I still enjoy discussing it.

So bare with me next time I will try to brush up before I post something like this again.
Thank: Ronald

 

[Rick Christopherson]

Details, details.

I have great respect for your knowledge, but you do have this propensity for being deliberately misleading, even when it comes to trivial facts such as the above. We would be on the same page far more often if you chose to be more honest with your intentions of your information. You skirt the bounds with jots and tittles without stepping over them, but the intention is deliberately deceptive.

 

[mivey]

I have great respect for your knowledge, but you do have this propensity for being deliberately misleading, even when it comes to trivial facts such as the above. We would be on the same page far more often if you chose to be more honest with your intentions of your information. You skirt the bounds with jots and tittles without stepping over them, but the intention is deliberately deceptive.

My sentence was no less or no more than the information provided by Besoeker.

Why the agenda? How is what I posted deceptive in the least? Where does it mislead anyone to anything? What position do you suggest I was trying to defend/counter/hide/whatever? Why does it always have to be a conspiracy theory with you? Why must you paint things to have some sinister purpose?

Perhaps these answers are the facts you should ponder.

Relax, dude.

 

[Besoeker]

Where does it mislead anyone to anything?

From another thread and directed at me:

You are trying to mislead me.

It happens....

 

[mivey]

From another thread and directed at me:

We should start a club.

I'm guessing it is just a matter of a habitual grab at the sad brush instead of the glad brush. I guess some of us are "half full" types and some are "half empty" types.

 

[Besoeker]

We should start a club.

I'm guessing it is just a matter of a habitual grab at the sad brush instead of the glad brush. I guess some of us are "half full" types and some are "half empty" types.

Possibly so.
I'm reminded of a saying that I have posted before:
"The beginning of understanding is the acknowledgement of ignorance."
Accepting and admitting that you don't understand something, particularly if it's in your field, seems harder for some than others. And maybe that's an age thing too.