MH's ideal coil and voltage question

[tinman]

The magnetic field of the inductor is still increasing through each time constant until it is 100% maximum value derived from steady current at the end of TC5. Only the RATE of increase in the source current/magnetic field is getting less with each TC.

The CEMF does not arise from the source current/magnetic field of the inductor per se, it arises from Changes in the source current/magnetic field of the inductor. The level of cemf is most dependent on the Rate of change of the source current/magnetic field not necessarily the strength of the magnetic field or amount of source current. At actual time =0, in a real world inductor, nothing happens really. But at 0+ picoseconds to microseconds the RATE of change is highest causing the maximum cemf to arise.

But cemf is not self sustaining because it is an emergent phenomena with a value based on rate of change of current/magnetic field, and there can be no more change if emf = cemf, so the cemf begins to drop, and as it does, more source current flows. The diminishing cemf still opposes the Rate Of Change of the source, but not the actual flow of current per se. In opposing the rate of change it diminishes the cause of its own existence. So the cemf diminishes in the familiar TC curve we see in all inductors.

Cheers

OK-good.
Now i want you to think about this very carefully Hoptoad-very carefully.

We have an ideal coil,and that is one free from any winding resistance. It is also void of a time constant--has none.
So from T=0,a voltage is applied across this ideal coil from an ideal voltage source-remember,no time constant,due to no winding resistance resistance.
At T=0,the current will continue to rise at a steady rate,and never reach a peak--the current rises to an infinite amount over an infinite amount of time. The CEMF as you said,is governed by the change in current flow induced by the applied voltage over time. But with our ideal coil,there is no change in current,as the current rises at a steady state for an infinite amount of time. So the current flow is the same as it was at T=0(-the moment a voltage was placed across the coil)for an infinite time.

Will the CEMF change from it's starting value(T=0),if the induced current from the applied voltage always rises at the same rate for an infinite amount of time?

P.S
To add your statement
Quote:  If the cemf was a steady value, all other factors would also be steady.


Brad

[tinman]

I strongly disagree. A voltage drop across a resistor is simply that. It can not be considered a "source" of emf or cemf. A resistor dissipates energy supplied by an emf. See the attached definition by Hyperphysics.

An emf is a source of energy. The voltage measured across a resistor is an indication of the dissipation of energy. Let's not confuse the two.

Thank you Poynt.
It is good to see some sanity still exist here.


Brad

[hoptoad]

OK-good.
Now i want you to think about this very carefully Hoptoad-very carefully.

We have an ideal coil,and that is one free from any winding resistance. It is also void of a time constant--has none.
So from T=0,a voltage is applied across this ideal coil from an ideal voltage source-remember,no time constant,due to no winding resistance resistance.
At T=0,the current will continue to rise at a steady rate,and never reach a peak--the current rises to an infinite amount over an infinite amount of time. The CEMF as you said,is governed by the change in current flow induced by the applied voltage over time. But with our ideal coil,there is no change in current,as the current rises at a steady state for an infinite amount of time. So the current flow is the same as it was at T=0(-the moment a voltage was placed across the coil)for an infinite time.

Will the CEMF change from it's starting value(T=0),if the induced current from the applied voltage always rises at the same rate for an infinite amount of time?


Brad

Good question - I don't know. The scenario you paint seems a bit like those dastardly 'which came first, the chicken or the egg' situations
Will have to sleep on that.
Cheers

[tinman]

I am not going to disagree with you strongly but I will add one caveat.  For starters, I already mentioned that several searches used the term "potential difference" for a resistor in a current loop with an EMF source.  So, indeed, a resistor is not a source of direct energy, but there is a tangible voltage associated with it.  "A source or perhaps instance of potential difference (when current is flowing through the device)" is a reasonable thing to say.

Let me explore the caveat.  Let's look at MOS-type semiconductors for a second.  When you get into the details of how they are constructed and how they function, it quickly becomes apparent that it's all about electrons and the moving about of electronics.  It starts to become an impediment to talk about current flow in these devices because it just gets too damn cumbersome.  So that's why they use the terms "source" and "drain" in that realm.  That refers of course to a source of electrons and a drain for electrons.

If you are in the realm of academic electrical engineering research, and looking at things on a deeper level, you may indeed use a different nomenclature.  I am talking purely hypothetically here.  When you start looking at voltage in detail, and you are snaking your way around a loop and observing the electric field, what do you see?  You typically observe very weak electric fields in wires, strong electric fields in capacitors, and as you snake your way through a resistor, depending on the value and the current flow, you can observe say a moderate or a very strong electric field.  In that realm of academic electrical engineering research, it may indeed be very convenient to refer to a resistor as a CEMF source because when you pass through it you can "go downhill" in terms of the electric field.

The realm of electronics and electrical engineering is so wide and so huge that different sectors will use their own rationalized units and use their own preferred nomenclature for devices and variables, etc.

So I am not "pushing" to say a resistor is a CEMF source, I am just saying that it may be valid to say that even if in this realm it's not an appropriate term.

MileHigh

Oh i see lol.

I say the very same thing as Poynt did,but i get a totally different reply.

To gutless to treat Poynt like you treat me?
Oh,and here is the kicker--the guy(me) that you think is such an amateur,and knows so little,gave the very same answer as Poynt,who is very well versed in EE--only i gave it first.

This speaks volumes about your true nature MH--your pathetic.


Brad

[MileHigh]

There is never a decrease or increase in the APPLIED EMF (voltage/current) source after connection. Remember - its an ideal voltage/current source to feed the ideal inductor.

In your standard example of an EMF source driving a resistor in series with an ideal coil then what you MUST look at is the APPLIED EMF ACROSS THE IDEAL COIL, and not the unchanging EMF source before the resistor.

Why is this?

Because as more current flows through the resistor the resistor causes an EMF DROP.

The EMF drop results in a new lower EMF across the ideal coil.

The ideal coil responds to the lower EMF imposed across it with an equal CEMF.

The lower EMF and the lower CEMF MUST BE EQUAL because they are CONNECTED to each other.

I know that I am really just repeating myself, try to understand it this second time.