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### Author Topic: MH's ideal coil and voltage question  (Read 428493 times)

#### poynt99

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##### Re: MH's ideal coil and voltage question
« Reply #360 on: May 14, 2016, 04:52:12 PM »
Make it any easier to understand now?

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

You need to draw in a voltage source, or function generator there.

#### verpies

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##### Re: MH's ideal coil and voltage question
« Reply #361 on: May 14, 2016, 04:53:57 PM »
Here verpies misinterprets my post as referring to your circuit diagram with the short. As I explained, that is not what I was referring to.
Yes, and I stand corrected.  I thought that you were referring to the circuit stipulated by Tinman and depicted in Fig.3.

#### poynt99

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##### Re: MH's ideal coil and voltage question
« Reply #362 on: May 14, 2016, 05:03:56 PM »
Yes, and I stand corrected.  I thought that you were referring to the circuit stipulated by Tinman and depicted in Fig.3.
Please draw out the current trace of your figure no. 3 then if V=1V and L=1H (both ideal).

If it is anything but an infinite amplitude, what is the point of illustrating it with a short circuit, other than to add confusion?

#### tinman

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##### Re: MH's ideal coil and voltage question
« Reply #363 on: May 14, 2016, 05:05:27 PM »

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

You need to draw in a voltage source, or function generator there.

If it has no internal resistance through that ideal voltage source,how can it not be a short circuit?

Please post a diagram you !your! ideal voltage source.

This is the paradox i am referring to,and why an ideal voltage source cannot exist,and/or be placed across an ideal inductor.
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 ?.

#### tinman

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##### Re: MH's ideal coil and voltage question
« Reply #364 on: May 14, 2016, 05:07:43 PM »
Please draw out the current trace of your figure no. 3 then if V=1V and L=1H (both ideal).

If it is anything but an infinite amplitude, what is the point of illustrating it with a short circuit, other than to add confusion?

Figure 3 represents MHs circuit.

#### MileHigh

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##### Re: MH's ideal coil and voltage question
« Reply #365 on: May 14, 2016, 05:10:40 PM »
Figure 2 represents my circuit.

#### tinman

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##### Re: MH's ideal coil and voltage question
« Reply #366 on: May 14, 2016, 05:18:41 PM »
Figure 2 represents my circuit.

No

Replace your ideal voltage source with an ideal capacitor,and you have the same.
an ideal capacitor is your voltage source,where that ideal capacitor has no series resistance.
You charge your capacitor to 4 volts,and you place it across your ideal coil.
Can you now measure a voltage anywhere around that circuit,even though current is now flowing through it?.

#### tinman

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##### Re: MH's ideal coil and voltage question
« Reply #367 on: May 14, 2016, 05:21:06 PM »
Please draw out the current trace of your figure no. 3 then if V=1V and L=1H (both ideal).

Quote
If it is anything but an infinite amplitude, what is the point of illustrating it with a short circuit, other than to add confusion?

It is to show you that you cannot place a voltage across a shorted(looped) ideal inductor.

#### MileHigh

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##### Re: MH's ideal coil and voltage question
« Reply #368 on: May 14, 2016, 05:22:10 PM »
Yes, and I stand corrected.  I thought that you were referring to the circuit stipulated by Tinman and depicted in Fig.3.

Verpies, this is mass confusion day.  I find your figure 3 confusing.  If we view a shorted ideal coil like a classic toroidal inductor, then aren't we talking about putting a voltage source across the toroid such that it ends up looking like two separate coils in parallel?

If that is the case, I fail to see any utility in that.

(sorry for the chicken scratchings drawing.)

#### verpies

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##### Re: MH's ideal coil and voltage question
« Reply #369 on: May 14, 2016, 05:22:41 PM »
Please draw out the current trace of your figure no. 3 then if V=1V and L=1H (both ideal).
In that case:
Current (i) flowing through the inductor equals i=ΔΦ/1H and the current flowing trough the voltage source is infinite.

#### MileHigh

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• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #370 on: May 14, 2016, 05:25:14 PM »
No

Replace your ideal voltage source with an ideal capacitor,and you have the same.
an ideal capacitor is your voltage source,where that ideal capacitor has no series resistance.
You charge your capacitor to 4 volts,and you place it across your ideal coil.
Can you now measure a voltage anywhere around that circuit,even though current is now flowing through it?.

No I assure you that figure 2 represents my circuit.

#### poynt99

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##### Re: MH's ideal coil and voltage question
« Reply #371 on: May 14, 2016, 05:29:30 PM »
If it has no internal resistance through that ideal voltage source,how can it not be a short circuit?
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.

Quote
Please post a diagram you !your! ideal voltage source.
It is a voltage source (set to voltage X) with a series resistor equaling 0 Ohms.

Quote
This is the paradox i am referring to,and why an ideal voltage source cannot exist,and/or be placed across an ideal inductor.
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.

Quote
What would happen if we reduced the internal resistance of a charged cap(say 1000uF with 10 volts across it) to a value of 0 ?.
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.

#### tinman

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##### Re: MH's ideal coil and voltage question
« Reply #372 on: May 14, 2016, 05:29:50 PM »
Verpies, this is mass confusion day.  I find your figure 3 confusing.  If we view a shorted ideal coil like a classic toroidal inductor, then aren't we talking about putting a voltage source across the toroid such that it ends up looking like two separate coils in parallel?

If that is the case, I fail to see any utility in that.

(sorry for the chicken scratchings drawing.)

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

#### verpies

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##### Re: MH's ideal coil and voltage question
« Reply #373 on: May 14, 2016, 05:31:47 PM »
Verpies, this is mass confusion day.
I kind of like it because it stimulates us to think.
I think this discussion is beneficial to all involved as long as Ad Hominem remarks are absent.

I find your figure 3 confusing.  If we view a shorted ideal coil like a classic toroidal inductor, then aren't we talking about putting a voltage source across the toroid such that it ends up looking like two separate coils in parallel?
The confusion will disappear immediately when you consider the coupling coefficient (k) between these two "separate coils" connected "in parallel".

In an ideal toroid the flux is completly shared and k=-1, thus in fact these coils are connected in anti-parallel when flux direction is considered. Thus they do not posses any inductance collectively. Consequently their anti-parallel combination possesses zero reactance and zero resistance, leading to zero impedance and the current flowing through the voltage source rises immediately to infinity.

If that is the case, I fail to see any utility in that.
It is pretty useless from an engineering standpoint, but it has a great educational value.
Anyway, it is what Tinman was referring to all along while you were apparently analyzing Fig.2.

#### poynt99

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##### Re: MH's ideal coil and voltage question
« Reply #374 on: May 14, 2016, 05:37:25 PM »
In that case:
Current (i) flowing through the inductor equals i=ΔΦ/1H and the current flowing trough the voltage source is infinite.