MH's ideal coil and voltage question

[MileHigh]

If R=0, then the current will climb at a steady rate fo all time-right?--no-wrong.
If the flow of current from T=0 is going to rise at a steady state,then the apposing current generated from the CEMF will also rise at a steady state. So what dose that mean for the current induced by the applied voltage?

It's  like i said MH , there is a big difference between having a small amount of resistance,and none at all. It is the difference between having a time constant,and not having one.
It is the difference between having a current trace curve over time,and not having one.

It is the difference of having water at 1*C and ice at 0*C

Brad

I have no clue what you really mean when you talk about "opposing current generated by the CEMF."  The CEMF does not generate any current.  If R = 0 in an ideal setup the current will rise indefinitely.  This has been covered already.

If there is a small amount of resistance vs. no resistance at all, and you evaluate situations where the time frame you are examining is much less than the time constant, then there will be negligible differences in the current for the two setups.  This has been covered several times already but I suppose that it did not stick. 

This is exhausting, going over the same material over and over.

MileHigh

[MileHigh]

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

As already stated, the energy is physically stored in the magnetic field in the 3D space around the coil.  Having a magnetic field in a given volume of space of a certain intensity takes real work.  It is magnetically stressed space.

I don't have a real hard core answer for you.  Just an observational answer.  When you observe a self-contained magnetic field structure in 3D space, say a classic toroidal doughnut shape around a coil, at the heart of that magnetic field structure there must be some circulating electric current.  That is what the structure is by definition, there are two components, but they are two parts of a single whole.

Electrons have mass, but the inertia associated with the moving mass is pretty insignificant.  However, the moving electron also subtends a magnetic field around itself when it is moving.  There is electrical inertia, i.e.; inductance associated with that also.  I am willing to bet you that the mechanical inertia and associated mechanical energy of an electron in motion at a given velocity is only a tiny tiny fraction of the electrical inertia and magnetic energy associated with an electron in motion at the same speed.  I am making a reasonable guess off the top of my head.

I am pretty sure the magnetic energy associated with an electron in motion is stated in the rationalized unit of the electron-volt.  What is the mass of an electron, something like 1/1830th the mass of a proton or neutron?

I am not looking anything up, I am too tired.

[tinman]

 
I have no clue what you really mean when you talk about "opposing current generated by the CEMF."  The CEMF does not generate any current.  If R = 0 in an ideal setup the current will rise indefinitely.  This has been covered already.

If there is a small amount of resistance vs. no resistance at all, and you evaluate situations where the time frame you are examining is much less than the time constant, then there will be negligible differences in the current for the two setups.  This has been covered several times already but I suppose that it did not stick. 

This is exhausting, going over the same material over and over.

MileHigh

No,this has not been covered already.

The CEMF is created by the changing magnetic field,which is due to the increasing current over time,that was induced when the voltage was placed across the inductor
This CEMF creates a current flow that is in the opposite direction to that of which the applied voltage induced. The value of the current flow produce by the CEMF is less than that induced by the applied voltage. It you take the peak current value that will be flowing at the 5th time constant,and you subtract from that the peak current value of the first time constant,you are left with the calculated reverse current produced by the CEMF. As you  can see,the current produced by the CEMF ,is less than that of the induced current by the applied voltage. This means the remaining difference is flowing through the coil at the end of the first time constant. The greatest amount of CEMF is produced at T=0,and so the greatest amount of reverse current is produced. This is why the inductor draws the least amount of current at T=0-because the difference between the revers current from the CEMF,and the induced current from the applied EMF ,is at a minimum.

The CEMFs value,and so the value of reverse current,is dependant on how much the magnetic field is changing over time. As the magnetics field change over time slows,less reverse current is produced,as the CEMF value is less. This is why the current induced by the voltage starts to rise over time.

If the current is going to continue to rise-such as it would in your question,then the magnetic field would continue to increase at a steady rate. If the magnetic fields change in time is a constant (as it would be for your ideal coil),then the CEMF would also be at a steady value-as Poynt has answered.

The magnetic fields rate of change over time  in a coil with no resistance,remains at a constant value,and that value is what it was at T=0--the instant the ideal voltage was placed across the ideal coil.
The current value will never increase from what it was as T=0,as the magnetic fields change over time remains at a constant value,and so the self induced EMF also remains at a constant value-->and there for,the reverse current also remains at a constant value.

So,regardless of what you believe, the answer to you question is--the current will not increase any higher than it was at T=0--regardless of the time the voltage is applied to the coil for.


Brad

[Magluvin]

 
I have no clue what you really mean when you talk about "opposing current generated by the CEMF."  The CEMF does not generate any current.  If R = 0 in an ideal setup the current will rise indefinitely.  This has been covered already.

If there is a small amount of resistance vs. no resistance at all, and you evaluate situations where the time frame you are examining is much less than the time constant, then there will be negligible differences in the current for the two setups.  This has been covered several times already but I suppose that it did not stick. 

This is exhausting, going over the same material over and over.

MileHigh

Ok. Another duh moment for me.  Must have been thinking of photons. I dunno.

Hmm. inertia of electrons.  I wonder. If we had a crt that was operating where electrons are attracted to the front screen, if we turned on and off the HV, would the electrons already firing toward the screen when the hv is off still make it to the screen.  Just thinkin.

And for the say suspended mag field, when we produce a field with coils and such, when we take the input away, the field wants to shrink or collapse. It hard to realize how the field is the supporting part in the continued current flow.

Im off to bed. Think more on it tomorrow.

Mags

[picowatt]

...

The magnetic fields rate of change over time  in a coil with no resistance,remains at a constant value,and that value is what it was at T=0--the instant the ideal voltage was placed across the ideal coil.
The current value will never increase from what it was as T=0,as the magnetic fields change over time remains at a constant value,and so the self induced EMF also remains at a constant value-->and there for,the reverse current also remains at a constant value.

So,regardless of what you believe, the answer to you question is--the current will not increase any higher than it was at T=0--regardless of the time the voltage is applied to the coil for.

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