MH's ideal coil and voltage question

[hoptoad]

The retaining wall at the end of the trough is stationary and does not move.  So think about the ramifications of that.

The wall doesn't have to move to absorb energy and be a part of the energy dissipation equation. But in your analogy, without including the wall there will be no compression of the spring, merely movement of the spring in the same direction as the cart.

When you lob a tennis ball against a wall, some energy is lost in sound through the air, and some energy of the ball is lost through heat by the distortion and rebounding of the balls shape and some will be lost to the wall itself in the form of pressure, heat and internal sound.

Any pressure of one object on another will create heat. The greater the pressure, the greater the heat. As the cart pushes the spring, the spring pushes the wall. Each component places pressure on the other and generates heat, the amount of which, however miniscule or large, being dependent on the pressure exerted.

Of course I'm explaining in terms of the unideal world, you know, reality, not ideal. Thats why I said you need an ideal wall to go with your ideal cart and ideal spring, for an ideal scenario, in which one can endlessly postulate about the 'ideal XYZ'.
However reality provides a way of supplanting postulation with knowledge through empirical evidence gained by observational research.

[MileHigh]

Hoptoad:

Here is the short definition for CEMF:

<<<
https://en.wikipedia.org/wiki/Counter-electromotive_force#cite_ref-Graf_1-0

The counter-electromotive force (abbreviated counter EMF, or CEMF),[1] also known as the back electromotive force, is the voltage, or electromotive force, that pushes against the current which induces it.
>>>

If you reread my example for the resistor and the inductor keeping the definition for CEMF in mind it should make sense.

For the trough, the best way of looking at it is to keep things simple.  You have a concrete trough that is hollowed out of the earth like a long and narrow swimming pool.  All four walls of the trough are fixed and immovable.  You put a long spring into the trough, and then a moveable cart moves forward with a constant velocity and pushes against the spring.

With that simple model all of the power expended to move the cart gets stored in the spring, and only in the spring.

MileHigh

[picowatt]

There is no difference between the EMF and the CEMF and current flows for both the resistor and the inductor.  Simple enough.

MH,

CEMF is typically used with reference to inductance.

As such, I believe most of us understand CEMF to be more so along the following:

A current flowing thru a conductor creates a magnetic field.  A portion of that magnetic field induces a rate of change dependent voltage into that same conductor.  The polarity of that induced voltage opposes the initial current flow thru the conductor.  It is that induced voltage, in opposition to the initial current flow, that is referred to as CEMF.

Can you provide a reference citing an example of your usage of CEMF with regard to resistors?

PW 

[tinman]

I am going to repeat my question to you Brad:

The ball is now in your court.  You say that the CEMF must be lower than the EMF for current to flow?  I have never seen any concrete examples of that from you.  Now is the time.  Show us some examples where the CEMF is lower than the EMF with all the specifics and all of the numbers crunched to explain how much current flows.

Forget about the motor example, and keep it simple and use a coil.  Give some examples providing all of the specifics and the EMF and CEMF values, the current flow, the whole nine yards.

MH

We have already done this with your ideal coil and ideal voltage.
We know the coil has a resistance value of 0 ohms--or no resistance.
What do you think it is that stops the current going straight to an infinite value,as soon as the voltage is placed across it?.
Why dose it take 3 seconds to reach a current of only 2.4 amp's,and not shoot up to an infinite amount of current flowing through that inductor.
What is the !reactance! in inductive reactance?-->what is reacting to what?
What is !self inductance! ?

You say the correct model is that the CEMF is less than the EMF?  Go ahead and give some examples with all of the details laid out so we can see if your model works or not.

I have the feeling that this is just your way of making me waste my time on something that is already very clear--except to you it seems.
So i have voted not to fall for this !waste of time! ploy by you,and instead,i give you a video that should make it very clear to you. As you will see,the circuit to show the effective CEMF is quite simple,and im sure i could show what he explains in the video.

I hope you listen to this video very carefully,and then you will understand that if the CEMF was equal to the EMF that produced it,there would be no current flow,as there would be no voltage drop/or potential difference across the inductor.

https://www.youtube.com/watch?v=RGTRXlarKww

But even then,i have a feeling we are going to see you !once again! try and change physics to suit your needs.


Brad

[hoptoad]

Hoptoad:
Here is the short definition for CEMF:
<<<
https://en.wikipedia.org/wiki/Counter-electromotive_force#cite_ref-Graf_1-0

The counter-electromotive force (abbreviated counter EMF, or CEMF),[1] also known as the back electromotive force, is the voltage, or electromotive force, that pushes against the current which induces it.
>>>
If you reread my example for the resistor and the inductor keeping the definition for CEMF in mind it should make sense.

For the trough, the best way of looking at it is to keep things simple.  You have a concrete trough that is hollowed out of the earth like a long and narrow swimming pool.  All four walls of the trough are fixed and immovable.  You put a long spring into the trough, and then a moveable cart moves forward with a constant velocity and pushes against the spring.

With that simple model all of the power expended to move the cart gets stored in the spring, and only in the spring.

MileHigh

I know what CEMF is and I know that even in the real world, technically every single circuit that has even a miniscule current will have some inductance, because a moving charge creates a magnetic field, and therefore exhibits a cemf opposing further changes to its own motion. I also know that in most real world circuits, inductance is disregarded when talking about resistors and semiconductors because the inductance of a resistor/semiconductor is so miniscule as to be irrelevent to its purposeful characteristics. When we want inductance we deliberately set about making it with a coil, not e.g. a carbon resistor.

As for your 'all four walls are fixed and immovable' in your cart analogy, if any single one of the walls is used as a backstop for the spring, then that wall becomes part of the energy dissipation system.( In reality, since all four walls are all part of the same entire mass of the trough, then the whole trough is part of the energy dissipation.)
You can not compress any spring from one side only. Try it without an anchor point like one of the walls, your spring would just move with the force applied to one side.

Go ahead, try to compress a spring by applying a force to one side without a backstop becoming an essential part of the system of components needed for the energy transfer required to compress it.

You don't need a concrete trough. Just a spring, your hand and .... whatever else is NEEDED to compress the spring.
Now I agree that most of the energy, even in a real world system, will get stored in the spring, but not all. The spring itself, unless ideal, will dissipate some of the compression energy it receives through heat due to lattice stress and displacement.
Only in an idealized world can perfect power transmission and storage take place.  Sadly we don't live in that world, we live in the real world, with circuit losses incurred and components that will never be 'ideal'.