MH's ideal coil and voltage question

[verpies]

It appears from your comment highlighted above, you assume that if an inductance is 100% efficient, it will not allow any current to flow.

His comment referred to current at t₀ only.
He never wrote that the current will be zero at  t₁.

The current will be totally impeded at all times (including t₁), only if the ideal inductor has infinite inductance.
An ideal inductor must have zero resistance but it does not need to have an infinite inductance (nor infinite reactance).

At 100% efficiency, the emf is totally cancelled by the cemf thus resulting in zero current flow or infinite inductance.  It must have even the smallest amount of resistance to perform like a real inductor.

No, an inductor does not need any resistance to perform its magic.  Ideal inductors impede current flow due to their reactance, not due to their resistance.

Also, efficiency is inversely proportional to the square of the resistance  because only resistance irreversibly converts energy to heat.  Inductive reactance does not irreversibly convert energy to heat - it converts it to magnetic field.  That conversion is lossless and reversible.

When we apply the formula delta I = E*t/L

The proper formula for current in a series RL circuit stimulated by a positive voltage step is:
i(t)= (V/R)*( 1-e^(-t*R/L) )

If you take it to the limit R-->0. then you get a linear current increase. (from zero if the inductor was not already energized at t₀)

[verpies]

Why isnt the CEMF ideal also when it comes to the ideal inductor?

Because the CEMF is a function of reactance, not of resistance.

An ideal inductor must have zero resistance but it does not need to have an infinite inductance (nor infinite reactance).

[partzman]

His comment referred to current at t₀ only.
He never wrote that the current will be zero at  t₁.

Mags agreed that I was correct with my assumptions so he will have to confirm what he really meant.

[/quote]

The current will be totally impeded at all times (including t₁), only if the ideal inductor has infinite inductance.
An ideal inductor must have zero resistance but it does not need to have an infinite inductance (nor infinite reactance).
No, an inductor does not need any resistance to perform its magic.  Ideal inductors impede current flow due to their reactance, not due to their resistance.
[/quote]

Yes I am fully aware of this. Let me make it clear that all of my first paragraph is stating what I assume Mags believes at this point in time and is not what I hold to believe. I apologize for my wording being confusing.

[/quote]

Also, efficiency is inversely proportional to the square of the resistance  because only resistance irreversibly converts energy to heat.  Inductive reactance does not irreversibly convert energy to heat - it converts it to magnetic field.  That conversion is lossless and reversible.
The proper formula for current in a series RL circuit stimulated by a positive voltage step is:
i(t)= (V/R)*( 1-e^(-t*R/L) )
[/quote]

Yes I agree but my reason for using the formula as stated is because no resistance is included so therefore it is assuming an ideal inductor which was my point.

[/quote]

If you take it to the limit R-->0. then you get a linear current increase. (from zero if the inductor was not already energized at t₀)
[/quote]

Yes I again agree.

partzman

[tinman]

I was agreeing with this as far as the wire resistance of a normal inductor being in series with the inductor, but when you got to the point where you stated "that entire circuit is closed by an ideal wire just like with an ideal inductor devoid of resistance" you lost me.

Are you referring to some circuit in particular or are you stating that the equivalent model for every inductor includes a short circuit across its terminals?

The model for a normal inductor has the wire resistance in series with the inductor.  The model for an ideal inductor removes that series resistor (or places its value at zero).  There is no short circuit across either inductor.

PW

Is this not the model below?
Regarding MHs question,will there not be an alternating current flow?
If we take into account that MH thinks DC means a steady state flow of current in one direction,then we would have to use the AC model to satisfy MH

Brad

[tinman]

Now there is your paradox Brad.

When you place an ideal voltage source across an ideal short, who wins? The voltage source or the ideal wire? verpies seems to indicate that the voltage source wins, as the voltage holds and the inductor still gets some current.

What you would get is a big explosion -the unstoppable force meets the unmovable object.
If there is a dead short across the ideal voltage supply,the current would simply build in the ideal voltage supply until either the short exploded,or the ideal voltage supply exploded. This would depend on which one of the two could contain the most energy before it failed-->or they(the shorted ideal wire and ideal voltage source) would continue to store the energy for an infinite time.


Brad