Difference between Voltage and Current

[USMC1302]

ggun: My senior design project was a pedal board of guitar effects, one of which was a tube distortion module. Had a heck of a time finding a socket to solder on my pc board. Generous old WW II radio operator that was a crack TV repair guy gave me one. I remember drug stores having a plug-in "tube checker", and I'm not that old ( I don't think anyway). Learned a lot that year. That rig could really pick-up WLS out of Chicago well....

 

[iceworm]

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.

From your posts I knew you had plenty of experience. Perhaps you noticed I pretty well alluded to that.

I've watched your posts plenty. You easily have the grasp of all the concepts.

I absolutely did not intend any disrespect.

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

Okay - Now I'm confused. I saw three separate references to mechanical analogies in the OP. But then again I am certainly not in any position to judge what you needed or didn't need.

I think a analogy is fine for a learning tool you can't do everything with math.

This is exactly what my post was about. Other than the hook, analogies are not particularly good learning tools. And, YES, one can do everything with the math. That is exactly what math models are about.

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.

Well, okay. But I am surprised that fits with ...

I know enough math to get by.

But I appreciate the offer though.

Offer? Do you mean the offer to send a diagram that would explain this?

When you study Electrical current flow you hear the statements about the current lagging behind or leading the voltage because of the effect of Induction and capacitance. Am I the only one that has a problem with this?"

If so, you're welcome. I do truly try and help. However since you don't need it and considering your comments about the math not being the answer (pun intended) then there really isn't thing I could add. I appologize for what turned into an empty offer.

Considering my reading of the OP, subsequence posts, and your response to my post 39, I clearly have no clue as your point. However, you are not under any obligation to change that. So that is okay.

Again, no disrespect intended.

ice (today a harmless flake spreading descruction):?

 

[kwired]

Instead of using water in pipe analogies use hydraulic or pheumatic analogies, otherwise people will think you are a plumber

 

[rattus]

Ronald, you must know calculus to fully understand current lead and lag in inductors and capacitors. Just remember that an inductor opposes a change in current. A capacitor opposes a change in voltage. When the waveforms are pure sinusoids, we can compute the inductive and capacitive reactances. If we know trig, we can then compute the PF of a reactive circuit.

 

[ronaldrc]

OK

That last post hurt just because I don't come across with a lot of math I must be ignorant
in the field.

I ask a fairly simple question about the voltage lagging behind the current. I got all kinds of response
but never did anyone ask me what I should have hear.



No pun intented but, Do you know or have you ever studied Apparent voltage this is what Charlie has been trying to say but he was so hot headed he could not think of the correct term.

Whats 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.

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

Ronald

 

[ronaldrc]

See:Rattus thats exactly what I'm talking about I study all that almost 40 years ago I don't use it
but its because I did forgot most of it. But if I want to use it I can it doesn't take a wizard to read formula and
apply the math with a calculator.

It doesn't take awizard to hook a complex control system but you sure couldn't do it just with a few equations.
After it is hook you can maybe study it and then apply your math and see what effect the active circuit elements will
have on that circuit. But please leave the terminations to an electrician.

Ronald:rant: :roll:

 

[ronaldrc]

Ice Worm, I do owe you an apology like Charlie I do get carried away sometimes.

Thats why I said its hard to argue with Charlie although I do think he is ones of the sharpest
Ees on here it wasn't meant as a compliment. Same holds true Rattus.

I said this might get controversial just didn't no I would end up being the ring leader.

I just have a different way of viewing these thing such as apparent voltage. I look at it as
another current created by the by the original current instead of apparent voltage.
Its really the same thing. Although I know you all will not agree.

It still has the same effect on the electrical system and you would still use your same math.

And please except my Apology. Ronald

 

[Rick Christopherson]

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.

There aren't very many good analogies for this because they can be fraught with problems, but consider moving a block of ice from point A to point B. The path from A to B is considered your goal, and constitutes real work. You push on the block towards the B-direction. You are performing real work toward your goal. However, if you have someone else pushing sideways on the block perpendicular to your desired path, they are not helping you out. They are not doing any real work to meet your goal. They will move the block, but not in the direction of your goal, so it is not real work to meet your goal. When you combine both of these "pushes" into a single diagonal push, only the component of this diagonal push that is in the direction of your goal, constitutes real work--that is your powerfactor.

This displacement between current and voltage is the result of delays within the devices to react to either their input current or input voltage. When you charge a capacitor, for example, it takes time for this build-up of charge (current) onto the plates for the voltage to be present across the plates. Because the voltage across a capacitor requires a build-up of charge on the plates (or a dissipation of charge), the voltage across a capacitor cannot change in an infinitely short period (it takes time to move this charge). The reverse is true for an inductor. Due to the magnetic field, the current through an inductor cannot change in an infinitely small period of time.

The common meme "ELI the ICE man" is one of the most common ways of remembering this. "ELI" means that when we apply a voltage (E) to an inductor (L), the current (I) will be behind the voltage--delayed from it. "ICE" means that when we apply a current (I) to a capacitor (C), the voltage (E) will be behind the current--delayed from it. It's all about delay, and why that delay exists.

 

[ronaldrc]

No Rick
Good information but I'm retired.

If you remember we invented apparent voltage around a week
ago on another thread. :roll:

Ok Then apparent power.

 

[rattus]

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.

 

[iceworm]

No Rick
Good information but I'm retired.

If you remember we invented apparent voltage around a week
ago on another thread. :roll:

Ok Then apparent power.

No, I missed the invention of apparent power. Is there a definition?

I'm back to work Monday, so I've only got today and tomorrow.

ice

 

[mivey]

No, I missed the invention of apparent power. Is there a definition?

Vrms x Irms

 

[iceworm]

Vrms x Irms

Not that one. I'm looking for the definitation invented last week.

ice

 

[rattus]

Not that one. I'm looking for the definitation invented last week.

ice

Apparently pfalcon claimed that the waveforms seen on a scope were apparent, but not real, because they were referenced to the neutral or some such nonsense.

Not to be confused with apparent power which is real or at least partially so. At least apparent power is well defined.

 

[__dan]

Please give me your thoughts on this. :Ronald

Without reading this thread ..

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.

If the unit is moving, that's current flow. A moving charge radiates a magnetic field that is coupled to other charged units. The coupling is very efficient. The entire modern world is built on the use of electromagnetic field properties.

Capacitors store energy in an electric field, inductors store energy in a magnetic field. The mechanical analogues are, the capacitor is a spring and the inductor is a shock absorber. The combination of the two elements are filters, like the springs and shocks in a truck.

Gravity pulls you to the earth. But it is electromagnetism that sticks all matter together and prevents you from fallng though the earth (Asimov).

 

[Rick Christopherson]

The unit electron has a negative charge and moves from + to -, greater to lesser height.

Oops. That's Ben Franklin's error because he mistakenly thought electrons had a positive charge. Electrons flow from negative to positive. Our convention for electrical current follows Franklin's error just to avoid reworking all of our previous equations. That's why we say electrical current flows the opposite direction from the actual electron flow.

 

[__dan]

The electron energy level falls from a higher to a lower energy level and radiates a photon, a unit quanta of energy. The electron absorbs a photon and is raised to a higher energy level. Just the same as a rock is raised up to a height or allowed to fall to a lower level.

Yes, you must be right, the electron moves from - to +. I am feeling like I have forgotten semiconductor circuits.

 

[rattus]

Too Much:

Too Much:

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

 

[Rick Christopherson]

I could be wrong about this, but I don't believe electron energy levels within an atom are related to an electron's propensity to move from negative to positive voltage potential. I think they are separate transfers. For example, an electron sitting at 4.8 eV is going to be propelled between the same potential difference at the same rate as an electron sitting at a 1.2 eV level.

When an electron moves from one energy level to the next, it absorbs or releases energy. 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.

An analogy to this would be a frying pan in a fire. In a fire, it has more internal energy than when in the refrigerator. Moving the frying pan in elevation through a gravity field does not change its heat energy. Aside from moving it so quickly that it heats up from friction, moving the frying pan from one height to another will not change its temperature (heat energy).

 

[__dan]

We are talking about several different effects. Electronic transitions are for bound electrons related to the number of protons of the atom were the electron is found. The electron occupies the atom valence shells which largely determine the material properties. Transition from one valence shell to another happens with the absorption or radiation of a photon. Transition within the atom or to the free, conductive state.

Free electrons are coupled to their enviroment, and radiate EMF when they move, by Maxwell's Laws. They're different effects.