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Author Topic: MH's ideal coil and voltage question  (Read 477831 times)

tinman

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Re: MH's ideal coil and voltage question
« Reply #345 on: May 14, 2016, 03:58:50 PM »
I'm not referring to tinman's circuit, but the original one stipulated by MH.

You were answering my question posted on my circuit diagram Poynt.
How can you say that you were referring to MHs question?

Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #346 on: May 14, 2016, 04:00:41 PM »
No to 1 & 2.

Thank you verpies
As we know,you are correct.

Brad

picowatt

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Re: MH's ideal coil and voltage question
« Reply #347 on: May 14, 2016, 04:07:29 PM »


A MH paradox added?

There is only one inductor--not a series of them.
My question was very clear.

Brad

Not a paradox, a model/tool for visualization purposes.

Every inductor can be thought of as being equivalent to a series string of inductors.

Would not measuring between several turns of your single inductor be equivalent to measuring between several series connected inductors?

PW

tinman

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Re: MH's ideal coil and voltage question
« Reply #348 on: May 14, 2016, 04:07:55 PM »
What are you saying exactly?

That an ideal inductor is one that has a short across its terminals? Please clarify your point.

No
An ideal inductor that is looped(has a short placed across it by an ideal wire)is a shorted ideal inductor. If there is no wire across the ideal inductor terminals,then it is just an open circuit.

Brad

verpies

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Re: MH's ideal coil and voltage question
« Reply #349 on: May 14, 2016, 04:08:29 PM »
The connection is not just a series connection when there is only two components.
The connection is both series and parallel.
Seemingly yes, if you do not count the ideal wire that shorts the inductor.
Pay attention to this issue and the associated terminology because in my opinion this is the reason why you and MH cannot agree.

The fact that the ideal voltage source has no internal resistance,and is connected across the ideal inductor,means the inductor is now a loop connection with no resistance to current flow through that now looped inductor.
Yes, there is no resistance to current flow but there is impedance to current flow.  That is why the current does not become infinite immediately.
Impedance has two components.  Please consider both of them.

partzman

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Re: MH's ideal coil and voltage question
« Reply #350 on: May 14, 2016, 04:11:42 PM »
Because an ideal voltage source has no internal resistance,and that is what makes it ideal.
The ideal voltage source is a series/parallel connection,as there is only two components in the circuit. As that ideal voltage source provides the very same link across the inductor as the piece of non resistant wire dose,then as soon as you hook the ideal voltage source across that ideal inductor,you have just shorted(looped) that ideal inductor.

If the voltage was reduced to 0 volts on the ideal voltage source,the current flow would continue through the loop that now exist in the ideal coil.=,as the voltage source has no internal resistance to impede the current flow.

Ask your self this.
When MH turns his voltage source down to a value of 0 volts,will the current flow continue on?
If not,then explain as to why not--what will impede that current flow,when the complete loop from the ideal inductor across the ideal voltage supply has no resistance ?

Who here can draw the complete circuit,along with the resistance values of that circuit?.


Brad

Let me first answer your question. When the ideal voltage source goes to zero volts, the current in the ideal coil will remain at the level it reached with the previous condition and will stay that way until the ideal voltage source is changed to a different magnitude.

What was confusing is that it appeared you wished to apply an ideal voltage across an ideal coil with an ideal short. This is not equivalent to the circuit as MH proposed.

The circuit diagram is simply an ideal source in parallel with an ideal inductor with no resistance.

partzman

picowatt

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Re: MH's ideal coil and voltage question
« Reply #351 on: May 14, 2016, 04:18:47 PM »
No, I believe that when the parasitic capacitance is disregarded then the inductors equivalent circuit has it wire resistance in series with its inductance and that entire circuit is closed by an ideal wire just like with an ideal inductor devoid of resistance.

I was agreeing with this as far as the wire resistance of a normal inductor being in series with the inductor, but when you got to the point where you stated "that entire circuit is closed by an ideal wire just like with an ideal inductor devoid of resistance" you lost me.

Are you referring to some circuit in particular or are you stating that the equivalent model for every inductor includes a short circuit across its terminals?

The model for a normal inductor has the wire resistance in series with the inductor.  The model for an ideal inductor removes that series resistor (or places its value at zero).  There is no short circuit across either inductor.

PW

poynt99

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Re: MH's ideal coil and voltage question
« Reply #352 on: May 14, 2016, 04:33:28 PM »
You were answering my question posted on my circuit diagram Poynt.
How can you say that you were referring to MHs question?

Brad
Well, actually I wasn't. What I was doing which led to my response was the following:

I think use of the term "shorted" when referring to an ideal inductor is not good nor accurate nomenclature.

An ideal inductor simply has zero series resistance. It is not "shorted" in any way, and will not present itself as a "short" if/when a voltage source (ideal or not) is connected across it.
Here I was responding to a post from verpies. Referring to an ideal inductor as being "shorted" brings no practical utility to the discussion other than to add confusion.

You need to think a little beyond what you are Poynt,and draw the circuit as MH said i should,
I have provided the definitions of the ideal voltage from an ideal voltage source,and an ideal inductor.

If an ideal inductor is shorted,so as it becomes an endless loop,can a voltage be measured anywhere across any two points of that(now looped) ideal inductor while a current is flowing through it?.


Brad

What is there that is beyond a voltage source and an inductor in series/parallel? I can draw it out in my head, what am I missing?

Let's throw in an ideal switch as well. What happens when the switch closes?

The second part of your question sounds like Faraday induction with the coil shorted.
Here I was responding to your response. Clearly I am referring to the original circuit, an ideal inductor with an ideal voltage source connected across it. Then I introduce an ideal switch. You said it yourself, "draw the circuit as MH asked you to", to paraphrase. There is nothing more to the circuit, specifically, no short across the inductor.

It seems that you are conflating the series connection of the voltage source with an inductor, with a parallel connection (across a shorted inductor) stipulated by Tinman.
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.

I would strongly suggest that all focus on the original question and purpose of this thread. I have now given you a clear illustration of the voltage source contained within the question, and reworded it to get directly to the point of the question.

So Brad, or Mags, will you give it a go? That is, plot out the current trace right over top of the voltage trace I posted?

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #353 on: May 14, 2016, 04:36:56 PM »
What was confusing is that it appeared you wished to apply an ideal voltage across an ideal coil with an ideal short. This is not equivalent to the circuit as MH proposed.

That's classic Brad.  From what I can gather the schematic that he posted did not match his written description from a few posts earlier, creating confusion.

tinman

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Re: MH's ideal coil and voltage question
« Reply #354 on: May 14, 2016, 04:37:18 PM »
Seemingly yes, if you do not count the ideal wire that shorts the inductor.
Pay attention to this issue and the associated terminology because in my opinion this is the reason why you and MH cannot agree.
Yes, there is no resistance to current flow but there is impedance to current flow.  That is why the current does not become infinite immediately.
Impedance has two components.  Please consider both of them.

Quote
Ideal inductors and capacitors have a purely imaginary reactive impedance:

Verpies
Can you define what they mean by !imaginary!,as this seems to only be associated with ideal inductors,where as non ideal(real world)inductors are always stated as having impedance,without the use of the word !imaginary! .

2nd-
If the ideal voltage source is reduced to a value of 0 volts instantly,but the non resistive link of the ideal voltage source is still across the ideal inductor,will the current continue to flow through the circuit,as there is nothing to impede this current flow.

Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #355 on: May 14, 2016, 04:42:56 PM »
Seemingly yes, if you do not count the ideal wire that shorts the inductor.
Pay attention to this issue and the associated terminology because in my opinion this is the reason why you and MH cannot agree.
  That is why the current does not become infinite immediately.
Impedance has two components.  Please consider both of them.

Quote
Yes, there is no resistance to current flow but there is impedance to current flow.

But that current flow must still be the same throughout the circuit/loop,regardless of the impedance created by the inductor.

As we have both stated,a voltage cannot be measured at any two points across a shorted ideal inductor. Adding the ideal voltage source to the open inductor,also shorts that inductor,due to the fact that the ideal voltage source also has no internal resistance--the loop is complete ,void of any resistance to current flow,regardless of the value of that current flow.

Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #356 on: May 14, 2016, 04:44:14 PM »
That's classic Brad.  From what I can gather the schematic that he posted did not match his written description from a few posts earlier, creating confusion.

The schematic i posted represents your circuit MH
Would it be easier if i placed a + and - sign in there for you ?


Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #357 on: May 14, 2016, 04:48:30 PM »
That's classic Brad.  From what I can gather the schematic that he posted did not match his written description from a few posts earlier, creating confusion.

Here is your circuit MH
Make it any easier to understand now?
The MH paradox?

Brad

poynt99

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Re: MH's ideal coil and voltage question
« Reply #358 on: May 14, 2016, 04:49:32 PM »
But that current flow must still be the same throughout the circuit/loop,regardless of the impedance created by the inductor.

As we have both stated,a voltage cannot be measured at any two points across a shorted ideal inductor. Adding the ideal voltage source to the open inductor,also shorts that inductor,due to the fact that the ideal voltage source also has no internal resistance--the loop is complete ,void of any resistance to current flow,regardless of the value of that current flow.

Brad
As the circuit is prescribed, there is always a voltage measured across the terminals of the inductor, and that voltage precisely follows what the voltage source is set to at any point in time.

minnie

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Re: MH's ideal coil and voltage question
« Reply #359 on: May 14, 2016, 04:51:40 PM »



   Most of you lot are very like lavatory brushes, clean round the bend!!
   Luckily we've got poynt to point us in the right direction.
   It's really good entertainment though.
         John.