MH's ideal coil and voltage question

[tinman]

Tinman,

You should research superconductors a bit.   

It's a huge field to weed thru, but there is both normal inductance (L) and kinetic inductance (L_k) associated with superconductors.

The kinetic inductance, L_k allows for operation up to and into the THz region and is exploited in radar components, such as antennas and phase shifters.  L_k allows low loss superconducting stripline techniques to be used rather than traditional and bulkier waveguides having more loss.

At lower frequencies where normal inductance applies, an 1800 RPM, 1MW, portable generator was constructed as a power source for a mobile radar system that uses superconductors in the rotor windings to reduce the generator's size.

Thousands of superconducting electromagnets (i.e., inductors) are in use everyday all over the world.

The field of zero resistance electronic components and specialized sensors is also a rapidly growing and heavily investigated field.

And then there is energy transport and storage, the list goes on...

You may argue that man made superconductors do not have a DCR of exactly zero.  In some cases that may be true, particularly with respect to high temp SC's.  Their resistance can range from 10^-9 to 10^-18 ohms of directly measured or calculated resistance.  However, some low temp SC's, which were believed to be less than 10^-28 ohms, the limits of measurement resolution (directly or by proxy), have since been measured by way of some rather unique methods that indicate they do indeed possess zero ohms of resistance. 

The point I am making is that zero DCR inductors (and other components) are in use everyday all over the world.  If an inductor made from a zero DCR conductor behaved as you propose, surely that would be a commonly known phenomenon by now.

Just food for thought...

PW

Ok,so we have our L ,as used to try and answer MHs question.
If the ideal coil is seen as a super conductor,then why was this !K! left out of all the measurements?.

As much as it may seem a waste of time to some,how about we go back to basics(that seem to be not so basic now),and determine a direct answer as to what stops the current flow through an inductor going straight to it's maximum value as soon as the voltage is placed across it.

My understanding is that the self induced EMF(CEMF) creates a current flow that apposes that which created it in the first place. The value of this CEMF is determined by the rate of change in time of the induced magnetic field.
The greatest rate of change in time for the magnetic field ,is at T=0-->the instant a voltage is placed across that coil,as we go from having no magnetic field,to one now existing at that point.
Then as time go's on,the rate of change of the magnetic field in time decreases.
This results in a lower value of this reverse current that is apposing the induced current by the applied voltage,and so the current flow through the inductor rises as the CEMF decreases over time.

Am i correct so far?.
And can we please forget about this ! a resistor creates a CEMF! rubbish.

P.S
I will add to this,that the reason that the resistance !seems! to increase with frequency,is because the magnetic fields change in time increases,and thus creates a larger CEMF in the inductor. What we are really doing,is bringing this overall change in time of the magnetic field,closer to that of the value it was at T=0. If we keep increasing the frequency,and thus increasing the rate of change over time for the magnetic field,we will reach a frequency where none/or very little current will flow through the inductor,as the increase in frequency has brought the rate of change of the magnetic field very close to what it was at T=0.


Brad

[Johan_1955]

You can accept it or not, but the actual reality is different and NOT covered in any textbook due to lack of need, and basic understanding.  2 other PhD's agree with me, but then quoted me one of Murphy's laws.  "Never argue with a fool, people might not know the difference."  In the context of this situation, they say I am the fool for expecting someone else's viewpoint to be even close to mine.

We know, the books are running years behind the ICE Tuning-Ateliers, this since years, the tuning Software even more, sorry!

With a Overlay in Exhaust and Inlet of a ICE, its a Serie-Cavity-Resonator, piece of Sheet-Metal called ........ is just a small part of the complete phenomena, what is almost not to catch in language its a understanding / knowing called Resonance, harmony and missing here grotesque!

To talk whit bookies, you have to talk there bookies-slang, other language than "The Haempstead" slang they don't willing understand.

OU is most dominated by RosaGlass-Followers, thinking they are in the lead, but out of compensation, and missing the best out of ........................ because of Dunnig-Kruger with a teacher syndrome!

Building NO.7!
Chemtrails!
Nasa!

Don't think, we do it for you!

[hoptoad]

In your standard example of an EMF source driving a resistor in series with an ideal coil then what you MUST look at is the APPLIED EMF ACROSS THE IDEAL COIL, and not the unchanging EMF source before the resistor.
Why is this?
Because as more current flows through the resistor the resistor causes an EMF DROP.
The EMF drop results in a new lower EMF across the ideal coil.
The ideal coil responds to the lower EMF imposed across it with an equal CEMF.
The lower EMF and the lower CEMF MUST BE EQUAL because they are CONNECTED to each other.
I know that I am really just repeating myself, try to understand it this second time.

Yes I understand and tentatively agree - for a theoretical 'Ideal' Inductor this would likely be the case. Although I'm not certain it would be, but I have no real actual knowledge to say it wouldn't. I misread one of your posts and simply didn't see the word 'net' in regard to the applied emf to the inductor. Qe Sera.

The circuit I posted a link to however is a good example of modeling what happens with a real inductor, with the internal resistance separated out and represented as an independent element from the inductor, in order to show the effective response of the inducance and resistance to the applied emf. The purpose of their circuit is to show the variation of the level of cemf and the resistance/inductance/voltage relationship with applied emf.

The circuit they use shows a separate Inductor and series resistor. Any real inductor circuit diagram that is drawn to convey the combined effect of the inductance and internal resistance would be represented the same way. The inductor in series with the (internal) resistance, with the internal resistance depicted externally.

As I see it this applies to real inductors :

snip...There are 2 voltage drops for the inductor, one is the self-induced voltage which is opposite of the source making it a drop, and the other is the resistance of the conductor part of the inductor.So you would have Vdrop1+Vdrop2=Vsource,, which then would have Vdrop1 going down and Vdrop2 staying constant and then when in a steady state condition Vdrop1 is gone leaving only Vdrop2.So as long as there is an R in the inductor the self-induced voltage will be less than the source,, but Vdrop1+Vdrop2 (that would make for the entire inductor and self-inductance) would equal Vsource.
snip...

Which leads back to one of tinmans statements that : 'the emf must be greater than the cemf for current to flow', with my added caveat - 'in a real inductor.'
What will happen in an 'ideal' inductor is great debating material, however, almost all explanations could be considered equally valid simply because the ideal doesn't exist (except possibly - inductors made with superconductors?) and therefore any hypothesis relating to it is (currently) unfalsifiable. But 'ideal' hypothesis do give the brain matter something to chew on.

Cheers

[tinman]

Cheers

Which leads back to one of tinmans statements that : 'the emf must be greater than the cemf for current to flow', with my added caveat - 'in a real inductor.'

Yes-for real(non ideal) inductors,we know this is true.

What will happen in an 'ideal' inductor is great debating material, however, almost all explanations could be considered equally valid simply because the ideal doesn't exist (except possibly - inductors made with superconductors?) and therefore any hypothesis relating to it is (currently) unfalsifiable. But 'ideal' hypothesis do give the brain matter something to chew on.

Indeed--what will happen?
The question deserved a better look than it go.
Instead of this being a thread to discuss the question as presented,the thread turned into a !!MH must be correct!! thread.
The mere fact that the coil has no resistance was in it self,worthy of a closer look. But it was just discarded,and so we removed the time constant from the equation,and went to plan B to find an answer.
We already know that the CEMF is what stops the current flowing through the coil,from shooting straight up to it's maximum value for that coil.
We also know,and have agreed on,that the current flowing through an ideal coil,with an ideal voltage across it,will rise in a steady state of increase for all time.
This can only mean that the magnetic field is changing at a steady state as well,and there for,the CEMF produced by that magnetic field will also be at a steady state.
So what dose happen from T=0s ?
Well,that is yet to be worked out,but i can tell you that it will not be the answer MH believes it should be,and that is the very reason that i said that i could(and did) provide the answer he wanted to see,but that i did not agree with that answer,or the equation used to get that answer.
The fact that the time constant is infinite,dose not just mean you dismiss it,and move onto another equation to derive at an answer you want to see.


Brad

[poynt99]

Here is what I posted to Poynt yesterday....

"If so, then the ideal conductor doesnt require energy for electrons to be stripped from atoms and move them from atom to atom, jumping shell to shell.  I can understand the seeming inertial effects of an inductor on electrons in its conductors, but not inertial effects of moving electrons on their own. This might incur that electrons have mass. And the seeming inertial effects of electrons of the inductor are when the field is collapsing. In this situation there is no field collapse or motion of the fields at all. So what mechanism keeps the electrons flowing in the loop? What energy is 'stored' that keeps the flow going? What form is the energy stored as?"


Mags

The energy in an inductor is stored as the magnetic field.

Dos your question pertain to steady current and when the inductor is shorted?