MH's ideal coil and voltage question

[partzman]

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

[picowatt]

I disagree.
Current can vary in an ideal shorted^* inductor only when the flux penetrating it is varied externally

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.

But despite that variance, there is no place to connect a voltmeter and measure the voltage or voltage drop.



^*  (shorted by an ideal wire, not by an ideal voltage source)

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? 

PW

[verpies]

I think this is an example of the root cause of one of Brad's problems:
<<< Why can a voltage not exist across a shorted ideal inductor that has current flowing through it>
Because V=IxR,and R=0  >>>
He keeps on going back to Ohm's law for an inductor.

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.

[poynt99]

To be more accurate,lets say the current is increasing at 800mA a second.

Brad

It doesn't matter really. All inductors, whether ideal or real will have a voltage across them when there is current through them, regardless if the current is changing or not.

[poynt99]

It seems that you are conflating the series connection of the voltage source with an inductor, with a parallel connection (across a shorted inductor) stipulated by Tinman.

I'm not referring to tinman's circuit, but the original one stipulated by MH.