MH's ideal coil and voltage question

[MileHigh]

When an inductor is first connected to a Voltage Source at time=0 and counting, the EMF and CEMF are EQUAL and their is NO current flow.

At end of TC 1 (TC = time constant of the inductor) the CEMF will be .37 of The EMF and supply current is flowing.
At end of TC 2 the CEMF will be .14 of The EMF and supply current is flowing.
At end of TC 3 the CEMF will be .5 of the EMF and supply current is flowing.
At end of TC 4 the CEMF will be .2 of the EMF and supply current is flowing.
At end of TC 5 the CEMF will be .0 of the EMF = non existent and supply current is flowing.

Any moment after that, the current through the inductor will be steady, the EMF will be steady and there will be NO CEMF.

MH, for someone who insists that others use the correct nomenclature when referring to circuitry, you seem to be pretty liberal with how you apply it yourself. Voltage drop across a component is not CEMF. EMF is not CEMF. Constant EMF is sustainable, constant CEMF is not.

Here's a link showing the relationship of CEMF in a series LR circuit, with the resistance external to the inductor and the presumption of an ideal inductor. Step through the exercise and answer the questions.

https://www.wisc-online.com/learn/career-clusters/stem/ace5903/an-inductor-opposing-a-current-change

Cheers

Yes Hoptoad, you are just describing the standard inverse exponential curve for the energizing of an ideal inductor in series with a resistor.  However you make a big fail in your reasoning and I will explain.

As the current increases through the (inductor + resistor) the net EMF presented across the inductor will be the original EMF minus the (resistor x current).

What that means is that over time the net EMF applied to the inductor decreases, and the CEMF generated by the inductor in response to the decreasing applied EMF is equal and opposite.

When an inductor is first connected to a Voltage Source at time=0 and counting, the EMF and CEMF are EQUAL and their is NO current flow.

And if the inductor was ideal and there was no resistance then after time=0 the CEMF will remain equal to the EMF and current will start to flow.

MH, for someone who insists that others use the correct nomenclature when referring to circuitry, you seem to be pretty liberal with how you apply it yourself. Voltage drop across a component is not CEMF. EMF is not CEMF. Constant EMF is sustainable, constant CEMF is not.

CEMF = counter electromotive force.  All that really means is a voltage that is opposite to the applied voltage.  Anything that generates an opposite voltage to the applied voltage can be considered a source of CEMF.  The good old "backwards battery in the circuit for charging" is a CEMF source.  Even a resistor can be considered a CEMF source but like I already posted, for clarity it is fine to call it a "potential difference" for a resistor.

I will repeat to you, a voltage drop across any component is actually a CEMF.  However, for sure it makes sense to try and keep the nomenclature simple and understandable for all.

MileHigh

[MileHigh]

Indeed. Anybody got an ideal inductor?

Every time you use the equation R = V/I, that assumes an ideal resistor.

Every time you use the equation v = L di/dt that assumes an ideal inductor.

Every time you use the equation i = C dv/dt that assumes an ideal capacitor.

All hobbyists and experimenters use the same equations day in and day out that are based on ideal components.

"Anybody got an ideal inductor?" is just bullshit talking.  I know that many of you play this "it ain't real" game but at the same time you unwittingly use equations that assume ideal components.

Don't resist the application of knowledge and reason when it makes you "uncomfortable."  Just get with the program because you are already assuming ideal components without even thinking about it.

[poynt99]

I didn't think I would have to spell it out in more detail, but looks as though I do.

Yes of course a real voltage source is not ideal, but compared to the output impedance of the coil, the voltage source is always going to appear as a heavy load, which is going to cause the cemf to go to practically 0V, if you were able to measure it, which of course you are not able to.

The point being, the cemf, no matter it's value, will effectively be shorted by the load. But as I explained there is no real consequence, because the resulting induced current does the job of limiting the current.

[MileHigh]

author=hoptoad link=topic=16589.msg486958#msg486958 date=1466674702]

It is good to see there is some one else that is not falling for MHs gobble doc.

But now 2 questions for you Hoptoad.
1-why dose the magnetic field that is inducing the CEMF,slowly decrease in change over time in an inductor from T=0-->moment of the applied voltage across the coil.
2-why is the CEMF equal to the applied EMF at the moment the voltage is placed across the coil?.

As i have said many times,MH changes things when it suit's his needs.
Do as i say--not as i do.

Indeed.

I doubt that will happen. MH is on a !!MH!! is right saga,and nothing gets in the way.

Brad

No, MileHigh responded to Hoptoad and when you read the reply you will see that the inductor's CEMF is equal and opposite to the decreasing EMF.  Hoptoad was wrong and it was clearly and unambiguously explained to him.

I have not changed a single thing to suit my needs.  This is all just collective mass hysteria, Night of the Living Anti-Kirchhoff Zombie Pod People.

[poynt99]

CEMF = counter electromotive force.  All that really means is a voltage that is opposite to the applied voltage.  Anything that generates an opposite voltage to the applied voltage can be considered a source of CEMF.  The good old "backwards battery in the circuit for charging" is a CEMF source.  Even a resistor can be considered a CEMF source but like I already posted, for clarity it is fine to call it a "potential difference" for a resistor.

I will repeat to you, a voltage drop across any component is actually a CEMF.  However, for sure it makes sense to try and keep the nomenclature simple and understandable for all.

MileHigh

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.