MH's ideal coil and voltage question

[picowatt]

I think we have to leave resistors of any kind out of this,as there is no such thing as an ideal resistor.
If a resistor did not dissipate energy,then it would have a resistive value of 0 ohms,and so,you have no resistor.

A resistor has no inductance,dose not store energy,and has resistance.
An ideal coil has inductance,dose store energy,and has no resistance.

The applied EMF see's the number of turns in the coil. The CEMF also see's the same number of turns in the coil.
As soon as the EMF induced current starts to flow,an equal and opposite CEMF produced current will start to flow,due to the fact that there are no losses associated to R.

Only when the RATE OF CHANGE of the current flowing thru the inductor equals .8 amps per second will the CEMF be equal to the applied EMF (with regard to the 4V applied to 5H).  For an ideal inductor, it does not matter if the actual current flowing is 1 amp or 1000 amps.  It is the RATE OF CHANGE that determines the CEMF.

The only reason the self induced current is of a lesser value to that of the EMF induced current in a real world inductor,is due to the losses associated to R in that inductor.

The resistance of a real world inductor is a source of error that causes the inductor's rate of change of the current flowing thru it to deviate from ideal (linear) and also limits the maximum current that can flow thru the inductor.

The formula for calculating the CEMF of an ideal inductor does not use or require a resistance.

PW

[poynt99]

I am a bit uncomfortable with this statement.

The CEMF is a generated effect due to induction.  A better visualization for the inductor's CEMF might be as a variable voltage source in series with a conductor.  The voltage of the variable voltage source is constantly adjusted as necessary to maintain the .8 amps per second rate of change to the current flowing thru the conductor (with regard MH's applied 4 volts and 5H inductor).

PW

(Added:  I am uncomfortable with the use of "dynamic resistor" as it seems to imply a dissipative mechanism)

Yes,

I should have qualified that with the fact that from the current profile perspective it acts just like a resistor that changes with time. But of course it would dissipate energy while the inductor does not.

[poynt99]

The instant 4V is applied to the inductor, the cemf goes to -4V and current begins to flow.

In the case of an ideal inductor there is no trade-off with a resistor, therefore the cemf remains constant (and equal to Vin) as does the rate of rise of the current.

Are we all in agreement?

[picowatt]

The instant 4V is applied to the inductor, the cemf goes to -4V and current begins to flow.

In the case of an ideal inductor there is no trade-off with a resistor, therefore the cemf remains constant (and equal to Vin) as does the rate of rise of the current.

Are we all in agreement?

If we are measuring across the inductor such that we see +4 volts, I would say that when the +4 volts is applied across the inductor, current begins to flow and as soon as the rate of change of that current flow reaches .8 amps per second, the inductor's CEMF also becomes +4 volts (not -4 volts).

PW

[poynt99]

I disagree PW.

The instant current begins to flow and rise, it is already rising at 0.8A/s (there is no gradual or "reaching" rise in current to the level of 0.8A/s). But we may be saying the same thing.

As far as the polarity of the cemf, yes it is the same as Vin.