MH's ideal coil and voltage question

[MileHigh]

Well they wont be two seperate coils in parallel MH,because one winding will be CW and the other CCW.
So they will be in series,not parallel

Brad

If it really was a toroid, then there will be two junction points where the voltage source makes contact with the toroid as shown in the diagram.  Current will flow say from top to bottom in each half coil.

There will be some flux cancellation at the two junction points.  But excluding that, for all practical intents and purposes each half of the toroid will be a separate and independent coil.  Because they are separate and independent, the winding direction is meaningless.

The two half-toroid coils will look like two separate coils in parallel across the voltage source.

MileHigh

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This is an addendum.....

Okay so Verpies is talking about an ideal toroidal inductor where there is total flux coupling from coil turn to coil turn no matter what the physical configuration.  It's almost like there is a "magic ideal core" to the toroid directing the flux.

In this case if you connect up the voltage source as per my diagram, the CW and the CCW turns due to the current splitting up in different directions will cause total flux cancellation and it will look like a direct short.

Note as per the toroidal inductor diagram, if the connections are not 180 degrees apart, you get a kind of "dial up an ideal inductor value" configuration.

I can get this but Verpies I think it had to be described better.  I hope I am right, and please correct me if I am wrong.

[tinman]

 author=poynt99 link=topic=16589.msg484272#msg484272 date=1463239770]

If it has 0V across it, then yes it is equivalent to a short circuit. However, this is a voltage source that starts out with +4V across it, therefore it must be drawn as an ideal voltage source or function generator.

And who states that this is the case?
Regardless of whether there is a voltage or not,the fact that there is no internal series resistance means that the current can still flow through that voltage source unimpeded.
When we drop down to 0 volts (as stated in MHs question),the current will continue to flow,and at a steady state. As verpies stated,you cannot measure a voltage across a shorted(looped) ideal inductor.

It is a voltage source (set to voltage X) with a series resistor equaling 0 Ohms.
There is no paradox. You are misinterpreting an ideal voltage source as a zero Ohm wire. That is not the case unless as I said, the voltage is set to 0V.

And MHs question requires a o voltage at one point in the test. At that point,the current still flow's,as there is no resistance that impedes that current flow through the now looped(shorted )circuit. Now,as virpies stated,you cannot place a voltage across a shorted ideal inductor,and you have just stated that at 0 volts,then yes,the ideal voltage source is like a 0 ohm wire. So now how do you once again increase the voltage after 0 volt's,as you are now trying to place a voltage across an ideal shorted(looped) inductor?

See the paradox now?.

Brad

You would have a good quality capacitor. What would happen? Nothing if it wasn't connected to anything. If connected to some load it would happily discharge.

Now we place that ideal inductor across that ideal capacitor--what happens?
Can you measure a voltage across any part of that circuit?.

[picowatt]

Figure 3 represents MHs circuit.


Brad

Figure 2 represents MH's question, and is an accurate representation of an ideal voltage source and inductor.

An ideal inductor is "theoretically" made from ideal wire having no resistance or capacitance.  It is not "shorted" by a wire having no resistance.

A straight length of ideal wire still has inductance and behaves accordingly.  Coiled up, that same length of ideal wire has increased inductance.  At no time is there any resistance in the ideal wire and at no time is there a requirement to short the inductor with another ideal wire to model it. 

PW

[verpies]

An ideal voltage source is not properly illustrated as a short circuit.

So what is the resistance of a 0V voltage source?
....or if you connect an ideal capacitor, charged to 11V, to an ideal 1V voltage source, then what current will flow through the capacitor at t₀?

[verpies]

What would happen if we reduced the internal series resistance of a charged cap(say 1000uF with 10 volts across it) to a value of 0(added),and then used that as our ideal voltage source,and placed the ideal inductor across it ?.

An ideal LC circuit will be formed and sinusoidal current will appear.
An infinite current will not flow because the ideal inductor will still possess non-zero reactance and impedance despite having zero resistance.