MH's ideal coil and voltage question

[MileHigh]

Look at this posting:  http://overunity.com/8341/joule-thief-101/msg483361/#msg483361

[poynt99]

Thanks MH for correcting me.

Although the question involves t=0 to t=13s, knowing what happens right at t=0 (the moment Vsource connects the inductor) is important.

It's also important to know what results when a number is divided by 0.

Let's see if examining this causes Brad to come to a different answer.

[Didymus]

Somebody has to go back to basics, it might as well be me.

The definition of an ideal inductor is a two-terminal device that obeys the current/voltage relationship:

V = L dI/dt  where V is the applied voltage, L is the inductance in Henries and dI/dt is the rate of change of the current with time.  The impedance of the voltage source and the resistance of the inductor are both assumed to be zero.

This definition can be rewritten as dI.dt = V/L.  Given an initial current of zero, applying 4 V to a 5 H inductor leads to a current through the inductor that increases at 0.8 amps per second.  After three seconds the current will be 2.4 amps.  If the supply is not turned off the current will increase indefinitely at 0.8 A/second.  There are no time constants involved.

For completeness, a capacitor is a two-terminal device the current through which is given by the equation:
I = C dV/dt where C is the capacitance in Farads.  The current through the capacitor is proportion to the rate of change in the applied voltage times the capacitance.  In this case applying a fixed current results in a voltage across the capacitor that increases indefinitely.

[Pirate88179]

Thanks MH for correcting me.

Although the question involves t=0 to t=13s, knowing what happens right at t=0 (the moment Vsource connects the inductor) is important.

It's also important to know what results when a number is divided by 0.

Let's see if examining this causes Brad to come to a different answer.

I just googled a few math sites and they all said that you can not divide any number by 0.  It is impossible and incorrect to do so.

So, now my question is...why is that?  One site said that you would get infinity by doing this which is why you can't do this.  Gee, and I thought I understood simple math, ha ha.

The intuitive answer, at least for me, would have been that division means breaking something into a certain number of equal parts and if there are no divisions into equal parts, then you are left with the original amount undivided.  But, this fails the multiplication test when you multiply the answer to double check it....

10 divided by 0 = 10.  Then 10 times 0 should equal 10, and of course it does not.  So, 10 divided by 0 either equals infinity, 0 or, it is undefined.  Some say it can't be done.  All of this depends upon which math sites you want to believe.

Bill

[Magluvin]

In an ideal voltage source the source Emf would be fixed and an ideal inductor would have virtually no losses. It seems to me no current could flow because the moment a charge tried to moved due to the ideal voltage source Emf the ideal inductor would produce an equal and opposite Cemf to oppose it. Ideally if the source Emf is always instantaneously opposed by the inductors Cemf then nothing can move, a stalemate.


AC

Lol. I said that a few times on this site. Just did yesterday.

Like are we taking about an ideal inductor that has no magnetic fields?  Like I said yesterday, it could be just the field charge before the ideal switch connects that could set up an ideal BEMF standoff and no current would ever flow, inductor or even a straight wire   Im glad someone here is on the same level of thinking as I am on this.    

Mags