MH's ideal coil and voltage question

[tinman]

Brad,

I am curious as to why you wish to apply an ideal voltage to a shorted ideal coil in reference to MH's original question? IMO, it really has no bearing. Perhaps this idea stems from the second condition of the question where zero volts is applied for 2 secs!?

In regards to an ideal voltage source not changing, we must qualify the change.  Assume for a moment that I am the creator of an ideal voltage source.  I am free from all known laws to set the voltage level at any magnitude I choose. The magnitude I choose however will not change with any attached load but I am still free to change the magnitude at any given time I wish. The output is still unable to change with any load variation.  This is the ideal voltage source MH used in his question.

partzman

Because an ideal voltage source has no internal resistance,and that is what makes it ideal.
The ideal voltage source is a series/parallel connection,as there is only two components in the circuit. As that ideal voltage source provides the very same link across the inductor as the piece of non resistant wire dose,then as soon as you hook the ideal voltage source across that ideal inductor,you have just shorted(looped) that ideal inductor.

If the voltage was reduced to 0 volts on the ideal voltage source,the current flow would continue through the loop that now exist in the ideal coil.=,as the voltage source has no internal resistance to impede the current flow.

Ask your self this.
When MH turns his voltage source down to a value of 0 volts,will the current flow continue on?
If not,then explain as to why not--what will impede that current flow,when the complete loop from the ideal inductor across the ideal voltage supply has no resistance ?

Who here can draw the complete circuit,along with the resistance values of that circuit?.


Brad

[picowatt]

I think he does and he is correct. 

Are you stating that you believe the equivalent circuit for an ideal inductor is an inductor in parallel with (shorted) by an ideal wire?

Do you also believe that the equivalent circuit for a normal inductor has its wire resistance in parallel with the inductor?

PW

[verpies]

The equivalent circuit model for an ideal inductor is not an inductor with a wire shorting across its ends.

Just because most of the world does it wrong does not mean that we have to.

An energized capacitor can be correctly modeled in an open state, the inductor - just the opposite.

Are you stating that you believe the equivalent circuit for an ideal inductor is an inductor in parallel with (shorted) by an ideal wire?

Yes, with an addendum that it can also be shorted by an ideal voltage source.
I know that SPICE does not draw an inductor this way, but internally it calculates it that way.

Do you also believe that the equivalent circuit for a normal inductor has its wire resistance in parallel with the inductor?

No, I believe that when the parasitic capacitance is disregarded then the real inductor's equivalent circuit has its wire resistance in series with its inductance and that entire circuit is closed by an ideal wire just like with an ideal inductor devoid of resistance.

[tinman]

Which is what I stipulated, that the current flowing had to vary over time to be able to measure a voltage as per the question.




PW

Consider a series string of ideal inductors connected into a loop with a shorting wire.  If you induce a time varying current into the loop, would there not be a measurable voltage drop between the inductors due to the reactance of those inductors?

A MH paradox added?

There is only one inductor--not a series of them.
My question was very clear.

Brad

[tinman]

Yes, the Ohm's law is not applicable to inductors because it totally disregards the reactance of the inductor.
Resistance is only one half of the total Impedance.  It actually is the reason why we have all these words to describe it.

But it is applicable when that ideal inductor is shorted(becomes a continual loop)
Even when a current is flowing through that looped ideal inductor,ohms law states that V=IxR,and as there is no R,then there is no voltage across that looped inductor--as we know.


Brad