MH's ideal coil and voltage question

[tinman]

As long as the current is rising at a steady rate of 0.8A/s, the cemf will be a steady 4V, it will not rise at a steady linear rate.
It is very unlikely anyone agrees with you. How are you going to prove this?

Ok -now we are getting somewhere.
If at T=0,4 volts is placed across the coil. The CEMF is also 4 volts as you state the moment current starts to flow.
So the outcome is?.-remembering that we have agreed (with the exception of MH-who seems to have his own ruels)that the CEMF has to be lower than the applied EMF in order for current to flow.


Brad

[tinman]

Again, to be clear, are you stating that you believe that the only amount of current that can flow thru an inductor with zero DC resistance is the amount of current that flows at T=0?

A simple yes or no would be most helpful.

PW

Going on what has been discused so far,and Poynt has stated that the CEMF value will be 4 volts,then why would current flow if the CEMF value is the same as the applied EMF?
We have all agreed that if the CEMF was the same value as the EMF ,then no current would flow.
So why would this change now?.

It would seem there  is a catch 22 situation here,and that is why i say the question deserves a closer look.


Brad

[tinman]

Sorry, but you sound incredibly stupid.  You have been playing with electronics all this time, for years, and you can't understand what a bloody voltage drop is?


MileHigh

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[poynt99]

Ok -now we are getting somewhere.
If at T=0,4 volts is placed across the coil. The CEMF is also 4 volts as you state the moment current starts to flow.
So the outcome is?.-remembering that we have agreed (with the exception of MH-who seems to have his own ruels)that the CEMF has to be lower than the applied EMF in order for current to flow.


Brad

The net outcome is that the current rises at a rate of 0.8A/s.

The details of how this happens don't seem available, and I have been offering a couple of ideas of my own in previous posts.

Ultimately, the inductor acts just like a resistor, but one that changes its value over time as I have previously described in detail. So it exhibits a voltage drop across its terminals, and it acts as a current limiter, albeit a dynamic one.

The mechanism of exactly how the cemf equals the emf while still permitting current flow is still somewhat of a mystery.

[tinman]

As long as the current is rising at a steady rate of 0.8A/s, the cemf will be a steady 4V, it will not rise at a steady linear rate.

The answer given for MHs question is not correct

It is very unlikely anyone agrees with you. How are you going to prove this?

You and others are going to do it for me . I only hope you  and others will take the time to read all i have gathered,as i have taken the time to put it altogether.

Quote post 1218-Poynt

I think you have the basic concept, yes. Again, the fundamental frequency and the harmonic content influences how the inductor reacts. The higher the inductance, the higher the induced cemf for a given frequency. At some point (either relatively large L or high frequencies) the cemf will equal the applied voltage (or it may be more correct to say the induced current will equal the applied current) and the net resulting current will be minimal.

Quote post 1227-MH

So even though the battery is imposing its voltage on the coil, you need to be able to shift your perspective and go "inside" the coil and realize that the coil is pushing back with the same CEMF. The applied EMF and the CEMF from the coil must add up to zero.  Therefore, the CEMF must be equal and opposite to the EMF.

Post 1231--Poynt

The voltage across the coil terminals does not change, it is determined by the voltage source. But the induced cemf is in series opposing with the voltage source Vin, and its value is determined by the frequency of Vin and the inductance L.
So, from this perspective the induced cemf is usually not equal to the applied emf (Vin). It is usually lower.

Then there is this confusing one by MH-post

I think that you are just going to confuse Brad with that diagram because he is going to see the CEMF being opposite the EMF

Then at the bottom of the same post,he say this

If you agree with this, then the CEMF is always equal and opposite to the applied EMF

So im lost with that one,as he says that i will get confused and think that the CEMF is opposite the EMF,and then go's on to say that it is

Post 1233--Poynt

I don't think he will assume that. I believe he knows that even though the induced emf (cemf) is opposite in polarity to that of the applied voltage, it will almost always be less, and therefore there will still be a net applied emf and resulting current.

Post 1282--Hoptoad,in reference to my statement--> if the CEMF was equal and opposite to the EMF,then the total voltage across the inductors terminals would be 0v,and no current would flow.

I agree. No potential difference, No current flow.

Post 1284 from PW

As well, it would seem that any device capable of producing a CEMF exactly equal to an applied EMF would prevent current flow.Consider two identical voltage sources connected in parallel (positive to positive, negative to negative).  One Vsource represents EMF and the other Vsource represents CEMF.  As long as both sources produce identical voltage, there will be no current flow.

Post 1297 from Hoptoad. I am going to post the link in that reply.

https://www.wisc-online.com/learn/career-clusters/stem/ace5903/an-inductor-opposing-a-current-change
You will see,if you follow the test pages,this statement.
Quote:  At 1 time constant,the CEMF cannot be sustained,and after the first time constant,the counter voltage reduces by 63%.
As our coil is ideal,we have no time constant,and the counter voltage will remain at a steady 4 volt,s--as you stated Poynt.

Post 1301-Citfta

If your claim that the CEMF equals the EMF were true then no current would flow

Post 1308 from Weby-a link attached

https://books.google.com/books?id=9dsWAAAAQBAJ&pg=PA268&lpg=PA268&dq=Is+a+resistance+a+CEMF?&source=bl&ots=OmxEsMZ6B2&sig=21Hvbdp3lsZo50GzV2t_DlJF7Bc&hl=en&sa=X&ved=0ahUKEwiRq4-Tm77NAhVC9GMKHegBCcgQ6AEIMjAI

A quote from that book regarding a DC motor.
Quote: If the BackEMF is equal to the applied EMF,then no current will flow through that motor. As we know,an increase in BackEMF means a decrease in current draw from the motor--this i showed in my last video very clearly.

Post 1313 by Hoptoad

If the cemf was a steady value, all other factors would also be steady.

Post 1331-Poynt

One is called cemf because that is precisely what it is; i.e. it is a generated voltage in this case. Going around the loop is simply confirming KVL, and it always holds.

Post 1332-Poynt

Since the amps/sec is constant, the induced cemf should be steady.See post 1313 above from Hoptoad

Post 1333 from PW

As I responded to Tinman, if it were somehow possible to cause all the magnetic flux created by a current flowing thru an ideal conductor to be confined to, and cut thru, that conductor in such a way as to make the inductor's CEMF be equal to the EMF, I believe that inductor would have infinite inductance.  To avoid the "chicken or egg paradox" in answering whether current could flow thru such an inductor, I stated that I believed that an infinitely small current would flow over an infinitely long period of time.

Post 1359--Loner

Again, if the CEMF were EXACTLY equal to the applied EMF, the "Rate of change" would be equal to 0,

Post 1363-Hoptoad

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.

And post 1446-Poynt

As long as the current is rising at a steady rate of 0.8A/s, the cemf will be a steady 4V,

At T=0 seconds the coil connects to the ideal voltage source. For three seconds the voltage is 4 volts

Post 1450-Poynt

The mechanism of exactly how the cemf equals the emf while still permitting current flow is still somewhat of a mystery.

Do i know what CEMF is?
To quote PW post 1399

 

Although a bit on the loose side where I pointed it out, his definition of CEMF was, for the most part, correct.

I believe that i have provided enough information by all here,that it is agreed upon,that if the CEMF value is equal to that of the applied EMF,then no current could flow.
It has also been concluded that the CEMF is Equal to the applied voltage at T=0.

In your last post Poynt(quoted above),you state that how the current can flow,when the CEMF value is equal to that of the applied EMF,is still a mystery.

So i ask-how is an accurate and correct answer gained from something yet unknown(the mystery),and also go's against all that most of us here believe to be true-even your self and PW ?.
You ask how am i going to provide proof to back up what i believe?. It would seem to me,that most of you here,are trying to find the proof that go's against all that has been stated in this thread-with the exception of MH,who provided a formula base around inductors/coils that have a resistance value.

I have spent the last 2 1/2 hours gathering all this information throughout this thread,and i only hope it dose not fall on death ears.


Brad