MH's ideal coil and voltage question

[picowatt]

Even though I said I would not post until I could show evidence contrary to your beliefs, I will play along.

The second Vsource or Cemf must be +4v of course.  And the point is .......?

pm

Edit: PW or anybody, please give an equivalent circuit or model of the Emf/Cemf interaction in a single inductor driven from an Emf source. Or a math derivation would be OK but not just the same repeat of Emf = Cemf please.

The point is that there is no minus sign where you indicated.

Everyone seems to be in agreement that no current will flow when the EMF=CEMF.

1.  When the current flowing thru a 5H inductor is changing at the rate of .8 amps per second, a CEMF of 4 volts is generated (CEMF=dI*L/dt).

2.  If the applied EMF is 4 also volts, current flow will cease as soon as the CEMF reaches 4 volts because at that point the CEMF equals the applied EMF (CEMF=EMF).

3.  However, as the current flow begins to cease, so does the rate of change, causing the CEMF to be less than 4 volts. 

4.  When the CEMF is less than 4 volts, that is, when the CEMF<EMF, current will again flow until the rate of change again reaches .8 amps per second and the CEMF again equals 4 volts.

Return to step 2 above (continuous loop)

And again, although described in a stepwise fashion, it is a smooth and continuous process similar to the many instances of negative feedback used in all manner of electronic circuits.

It is this process that limits, or regulates, the current flow's rate of change.

PW

[partzman]

The point is that there is no minus sign where you indicated.

Everyone seems to be in agreement that no current will flow when the EMF=CEMF.

No current flow in what? Could you be specific as you reference Emf=Cemf below in your feedback correction example below when dI=.8A/S.

1.  When the current flowing thru a 5H inductor is changing at the rate of .8 amps per second, a CEMF of 4 volts is generated (CEMF=dI*L/dt).

Well I guess that I'm the only one who disagrees so I will try to explain why! Why are you taking liberty to change Cemf=-dI*L/dt to Cemf=dI*L/dt? Are you throwing the Lenz factor away? If yes, why and how? If not, then when you state that Emf = Cemf, to me you are saying to me that dI*L/dt=-dI*L/dt. Do I not understand the terminology?

2.  If the applied EMF is 4 also volts, current flow will cease as soon as the CEMF reaches 4 volts because at that point the CEMF equals the applied EMF (CEMF=EMF).

Now I'm really confused by the above statement because you and others hold to the idea that Emf = Cemf during normal inductor current so again, what current will cease to flow?

3.  However, as the current flow begins to cease, so does the rate of change, causing the CEMF to be less than 4 volts.

OK, let's look at what could cause the current in the inductor to decrease even slightly during any given dt.  A), the Emf could drop but so would the assumed Cemf so we still follow the EMF law. B), the inductance could change due to self heating (neglecting any change in the DC resistance) creating a slight physical movement so this could really be ignored, but this too would follow the Emf law. So what does that leave but C), the initial instant that the Emf is applied when supposedly the Emf/Cemf feedback loop corrects until we experience dI=Emf*dt/L.

4.  When the CEMF is less than 4 volts, that is, when the CEMF<EMF, current will again flow until the rate the change again reaches .8 amps per second and the CEMF again equals 4 volts.

Again, apart from any outside influence such as an approaching magnet or any material that would change the permeability, what would cause the required feedback adjustment above other than the instant of applied Emf?

Return to step 2 above (continuous loop)

And again, although described in a stepwise fashion, it is a smooth and continuous process similar to the many instances of negative feedback used in all manner of electronic circuits.

PW

Well, I can't seem to get past step 1.   Believe me, I understand what you are trying to explain, I just don't agree with it for the above and previously stated reasons.

IMO, your thought model is flawed but I just can't prove it at this point in time.

pm

[Magluvin]

The point is that there is no minus sign where you indicated.

Everyone seems to be in agreement that no current will flow when the EMF=CEMF.

1.  When the current flowing thru a 5H inductor is changing at the rate of .8 amps per second, a CEMF of 4 volts is generated (CEMF=dI*L/dt).

2.  If the applied EMF is 4 also volts, current flow will cease as soon as the CEMF reaches 4 volts because at that point the CEMF equals the applied EMF (CEMF=EMF).

3.  However, as the current flow begins to cease, so does the rate of change, causing the CEMF to be less than 4 volts. 

4.  When the CEMF is less than 4 volts, that is, when the CEMF<EMF, current will again flow until the rate of change again reaches .8 amps per second and the CEMF again equals 4 volts.

Return to step 2 above (continuous loop)

And again, although described in a stepwise fashion, it is a smooth and continuous process similar to the many instances of negative feedback used in all manner of electronic circuits.

It is this process that limits, or regulates, the current flow's rate of change.

PW

Are we talking about cemf of the inductor or an applied cemf equal to the applied emf?

When we first apply 4v emf, how can cemf be equal to the emf? What happened to create the initial cemf? Did some current flow in the beginning due to emf in order for the cemf to develop in the first place? I mean, I can understand that at T0 that the 4v can be read across the inductor leads, but Im not sure it is due to cemf created by induction unless some initial emf current must have happened in order for cemf to develop in the first place.


Im kinda betting on cemf to be in some form, no matter how small the difference, to be always less than the emf.

Mags

[picowatt]

Are we talking about cemf of the inductor or an applied cemf equal to the applied emf?

When we first apply 4v emf, how can cemf be equal to the emf? What happened to create the initial cemf? Did some current flow in the beginning due to emf in order for the cemf to develop in the first place? I mean, I can understand that at T0 that the 4v can be read across the inductor leads, but Im not sure it is due to cemf created by induction unless some initial emf current must have happened in order for cemf to develop in the first place.


Im kinda betting on cemf to be in some form, no matter how small the difference, to be always less than the emf.

Mags

All thru this thread we have been discussing the 4 volts applied across the inductor from an ideal Vsource ,as being the applied EMF, or just EMF.  The EMF is the fixed potential of 4 volts applied to the inductor at T=0.

CEMF refers to the voltage induced in the inductor's windings as the current flowing thru the inductor changes at a speciific rate.

PW

[picowatt]

Has everyone at least read the Wiki?

https://en.wikipedia.org/wiki/Inductor

PW