MH's ideal coil and voltage question

[MileHigh]

Attached is an equivalent circuit of MH's question using ideal components.  The questions are, can we vary Vg and can we use delta I = E*t/L to analyze this circuit? If not, why? The main objection has been the short circuited this and that. I don't see any short circuits.  What an I missing here?

partzman

You are absolutely 100% dead on.  Will the train see the light at the end of the tunnel and actually emerge from the tunnel in one piece?  That is the question of the hour.

[Magluvin]

As I said, I am not arguing against that.
The short is not removed. The voltage source itself is the short (if you will), but it doesn't short itself out!
There is no paradox, and verpies is wrong because the inductor does not represent a short the moment it is connected to something, even an ideal voltage source. The only true paradox I've seen so far is verpies' application of an ideal voltage source across an ideal short. Which one wins? That is your paradox Brad.

As I said, talk of such abstract theories as being posed is not helping the understanding here in any way, it is only hindering it.

I agree with you on the no current flow at t/0 of an ideal inductor. 

But I dont think that if we're to study the ideals if an ideal inductor that we should ignore the mechanism that makes it do what it does. If resistance is zero, and no losses, then that underlying ideal inductor mechanism should be lossless and 100% efficient also. And if that mechanism is lossless then the the inductor should continuously impede an emf presented at the input.    PW says that a straight wire has inductance, and I agree, no matter how tiny the inductance is. So it may be that the ideal straight wire may not be able to pass current if the inductance mechanism is 100% efficient. Does that make any sense at all? If not then where might we find reference that tells us otherwise so we can examine that if possible?

In the real world we have resistance mostly no matter what. So all those losses, voltage drops no matter how tiny would definitely affect the efficiency of that mechanism to be less than 100% efficient, thus there could not be a 100% impediment to the input and the inductor would now work as we know them.

Mags

[Magluvin]

I agree with you on the no current flow at t/0 of an ideal inductor. 

But I dont think that if we're to study the ideals if an ideal inductor that we should ignore the mechanism that makes it do what it does. If resistance is zero, and no losses, then that underlying ideal inductor mechanism should be lossless and 100% efficient also. And if that mechanism is lossless then the the inductor should continuously impede an emf presented at the input.    PW says that a straight wire has inductance, and I agree, no matter how tiny the inductance is. So it may be that the ideal straight wire may not be able to pass current if the inductance mechanism is 100% efficient. Does that make any sense at all? If not then where might we find reference that tells us otherwise so we can examine that if possible?

In the real world we have resistance mostly no mater what. So all those losses, voltage drops no matter how tiny would definitely affect the efficiency of that mechanism to be less than 100% efficient, thus there could not be a 100% impediment to the input and the inductor would now work as we know them.

Mags

See, something MH said bothered me a bit. He said that a resistance of .000001ohm,  1uohm was virtually seemless to being an ideal inductor. Would you agree with that statement? Not trying to pit you against him. But it would be nice if that statement were to be considered true by you or not and give us your understanding as to why your answer is what it is. 

I say it is very far from seamless, pretend world or not.   It was said by Carl Segan that if we cut an apple pie in half, then cut 1 half in half, then cut 1/4 in half, and keep going, I think the number was about 70 or 90 cuts to get to a single atom.  It was less than 100 cuts. But we could go further and further, somehow. When does it end?   So the '1uohm is seamless with an ideal component' is not an accurate statement and we cannot accept that as fact here. .5uohm  has half the resistance of his idealized 1uohm. What about .001uohm? .001 pico ohm?  .000000001pico ohm?    So I think that should be resolved on that seamless bit. It is not a good representation, of which happens quite often.


Mags

[Magluvin]

See, something MH said bothered me a bit. He said that a resistance of .000001ohm,  1uohm was virtually seemless to being an ideal inductor. Would you agree with that statement? Not trying to pit you against him. But it would be nice if that statement were to be considered true by you or not and give us your understanding as to why your answer is what it is. 

I say it is very far from seamless, pretend world or not.   It was said by Carl Segan that if we cut an apple pie in half, then cut 1 half in half, then cut 1/4 in half, and keep going, I think the number was about 70 or 90 cuts to get to a single atom.  It was less than 100 cuts. But we could go further and further, somehow. When does it end?   So the '1uohm is seamless with an ideal component' is not an accurate statement and we cannot accept that as fact here. .5uohm  has half the resistance of his idealized 1uohm. What about .001uohm? .001 pico ohm?  .000000001pico ohm?    So I think that should be resolved on that seamless bit. It is not a good representation, of which happens quite often.


Mags

Cut that 1uohm in half, 90 times.  Are we done yet? Are we on the verge of an ideal component with zero losses yet?

Mags

[partzman]

I agree with you on the no current flow at t/0 of an ideal inductor. 

But I dont think that if we're to study the ideals if an ideal inductor that we should ignore the mechanism that makes it do what it does. If resistance is zero, and no losses, then that underlying ideal inductor mechanism should be lossless and 100% efficient also. And if that mechanism is lossless then the the inductor should continuously impede an emf presented at the input.    PW says that a straight wire has inductance, and I agree, no matter how tiny the inductance is. So it may be that the ideal straight wire may not be able to pass current if the inductance mechanism is 100% efficient. Does that make any sense at all? If not then where might we find reference that tells us otherwise so we can examine that if possible?

In the real world we have resistance mostly no matter what. So all those losses, voltage drops no matter how tiny would definitely affect the efficiency of that mechanism to be less than 100% efficient, thus there could not be a 100% impediment to the input and the inductor would now work as we know them.

Mags

Mags,

I am not the one you asked for an answer on this but I will go ahead and offer my opinion.  It appears from your comment highlighted above, you assume that if an inductance is 100% efficient, it will not allow any current to flow. 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.

When we apply the formula delta I = E*t/L or rearrange the formula to solve for inductance of emf, we assume ideal conditions such as an ideal inductance.  The answer we get from using this formula on an inductance with resistance is very close to what we would measure on the bench. The less dc resistance the coil has, the closer the answer is. From this we can deduce that an ideal 5h inductance is just that, 5h with no impediment from any resistance.

partzman