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Author Topic: MH's ideal coil and voltage question  (Read 477801 times)

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #105 on: May 09, 2016, 08:21:40 PM »
Quote
one thing that majorly confused me, and apparently you as well, was the 'ideal voltage' source also being a variable supply. so not only does this magic power supply provide infinite current with 0 vdrop it can change voltage at any time. I was under the impression an ideal vsource was a fixed source for all intents and purposes, though apparently not.

That's an ironic twist for you.  The supposedly "open-minded researchers that go where conventional scientists don't dare go" can sometimes be so closed-minded that they can't conceive of something as simple as an ideal voltage source that varies in time.

Magneticitist

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Re: MH's ideal coil and voltage question
« Reply #106 on: May 09, 2016, 08:28:29 PM »
That's an ironic twist for you.  The supposedly "open-minded researchers that go where conventional scientists don't dare go" can sometimes be so closed-minded that they can't conceive of something as simple as an ideal voltage source that varies in time.


it's quite simple.. having not invested any real time into learning about 'ideal' components, I had to look up what constituted an ideal voltage source.. The information I gathered stated an ideal voltage source was a fixed source that can supply infinite current without dropping.. Obviously that was an incorrect or incomplete description.
(i will say that yes, the possibility of a variable supply did indeed fly over my head. I won't cry about it!)
Now you're just being spiteful.

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #107 on: May 09, 2016, 08:28:41 PM »
I'm not being sarcastic at all.

Unless I'm overlooking something, or don't correctly understand the question, there will be no current, and the voltage across the inductor will be whatever the voltage source is at any one time, from t=0 to the end of time.

Given that tau=infinity, there can be no change in either I or V. Indeed if R is non-zero, there will be a current and the voltage change over time.

I am going to have to assume that you don't understand the question.  Before t=0 the voltage source and the coil are disconnected.  The only reason for putting it that way is to implicitly establish that the current through the coil is zero at the start of the test.  At t=0 you then have a 4-volt source connected to a 5-Henry inductor, and then the voltage varies in time as described.

When it is reworded as above, is it clear now?

poynt99

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Re: MH's ideal coil and voltage question
« Reply #108 on: May 09, 2016, 08:29:57 PM »
Brad,

I don't support your answer regarding the inductor acting like an instantaneous short. Just because there is no current flow, doesn't mean the load presented to the voltage source is no longer "inductive".

There is only one answer, that being the inductor will essentially look like a perpetual "open" to the voltage source. At least that is my thinking on this until MH corrects me, and I welcome being corrected if I am in fact wrong on this.

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #109 on: May 09, 2016, 08:31:05 PM »

it's quite simple.. having not invested any real time into learning about 'ideal' components, I had to look up what constituted an ideal voltage source.. The information I gathered stated an ideal voltage source was a fixed source that can supply infinite current without dropping.. Obviously that was an incorrect or incomplete description.

Now you're just being spiteful.

They say fixed source meaning that the voltage will not change under load.  They don't say anything else.

tinman

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Re: MH's ideal coil and voltage question
« Reply #110 on: May 09, 2016, 08:32:29 PM »
Brad:

I will repeat this a second and last time.  The addition of the resistance to the simulation is to solve a constraint in the way the software works.  It has nothing whatsoever to do with what you are referring to.



You literally have been given a partial correct answer from partzman in two forms.  Someone else earlier in the thread described an ideal inductor behaviour perfectly.  It looks like it's going to take a few more days before you come round and it may have to end up being a forced spoon feeding session from a guru.

MileHigh

MH
Maybe you can work out the L/R time constant of an ideal coil.
As Poynt stated,and as i stated,it will then be 5/0=infinity.
You have already stated that there is no time constant,and the value could be infinity or undefined-correct?,or do i have that wrong?.

If it is infinity,then there is going to be no current flow into the ideal inductor-correct?

So unless you know some sort of math that allows a division of 5/0,and provides a value we can work with,then i will stick with my claim.

Quote
You are in for an unpleasant surprise when Poynt comes back.  You think that both of you are on the same page but you are not.  Like I said, I can't explain his quote but in due time we will find out.

Well i dont believe that Poynt would lead me down the garden path,or post sarcastic results,just because that is what i believe. Sure,we have had our moments,but we have also had our times where we get along just fine,like in the Lewin topic not long ago. I listened to what he was saying,and carried out the test as he stated,and it resulted in being exactly what he said it would be. There is always going to be times when we dont agree on something,but when it comes time to work on thing's like this,then we should both be striving toward a correct answer and outcome.

Brad.

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #111 on: May 09, 2016, 08:34:51 PM »
Brad:

<<< If it is infinity,then there is going to be no current flow into the ideal inductor-correct?  >>>

Here is something for you to ponder:  A straight line is a circle with a radius of infinity.

Magneticitist

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Re: MH's ideal coil and voltage question
« Reply #112 on: May 09, 2016, 08:35:33 PM »
I also want to point out in a non sarcastic manner, that this is what it's all about. despite our little beefs we are trying to put our minds together to debate and brainstorm what's going on here... From the EE professionals to the casual tinkerers it's not so cut and clear... this is how complex electricity can be..

I'm not saying a simple agreeable answer is impossible... but clearly if one 'side' has yet to clearly come to an agreeable conclusion then it must be, at the very least, a little confusing.

Magneticitist

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Re: MH's ideal coil and voltage question
« Reply #113 on: May 09, 2016, 08:37:00 PM »
They say fixed source meaning that the voltage will not change under load.  They don't say anything else.


well in all honestly my mistake then.. but I took 'fixed source' as being utterly fixed.

tinman

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Re: MH's ideal coil and voltage question
« Reply #114 on: May 09, 2016, 08:37:02 PM »
Brad,

I don't support your answer regarding the inductor acting like an instantaneous short. Just because there is no current flow, doesn't mean the load presented to the voltage source is no longer "inductive".

There is only one answer, that being the inductor will essentially look like a perpetual "open" to the voltage source. At least that is my thinking on this until MH corrects me, and I welcome being corrected if I am in fact wrong on this.

OK,so here is the part in that reply i dont understand.
If the inductor looks like a perpetual open (circuit i guess?)to the voltage source,then what is the load?

Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #115 on: May 09, 2016, 08:38:56 PM »
Brad:

<<< If it is infinity,then there is going to be no current flow into the ideal inductor-correct?  >>>

Here is something for you to ponder:  A straight line is a circle with a radius of infinity.

A straight line is not a circle,as it has a beginig and end-unless it is infinitely long. A circle is an infinite loop.


Brad

poynt99

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Re: MH's ideal coil and voltage question
« Reply #116 on: May 09, 2016, 08:39:25 PM »
OK,so here is the part in that reply i dont understand.
If the inductor looks like a perpetual open (circuit i guess?)to the voltage source,then what is the load?

Brad

Zero current means no load. So we have an infinite load, i.e. an "open" circuit.

tinman

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Re: MH's ideal coil and voltage question
« Reply #117 on: May 09, 2016, 08:44:52 PM »
I'm not being sarcastic at all.

Unless I'm overlooking something, or don't correctly understand the question, there will be no current, and the voltage across the inductor will be whatever the voltage source is at any one time, from t=0 to the end of time.

Given that tau=infinity, there can be no change in either I or V. Indeed if R is non-zero, there will be a current and the voltage change over time.

Thanks Poynt
I did not believe that you would answer questions this important in a sarcastic manner -as i pointed out to MH.

So this would mean that MHs original question would result in the applied voltage being seen across the ideal inductor,and nothing more than that.

So rather that slam all my theories in one post,maybe a step at a time would be better.

So,if there is no current flowing through the inductor,that would mean no inductance/no resulting rising magnetic field?--correct?


Brad

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #118 on: May 09, 2016, 08:45:08 PM »
<<< You have already stated that there is no time constant,and the value could be infinity or undefined-correct?,or do i have that wrong?. >>>

Here is the reason I am saying there is no time constant:  It's because in the ideal coil case you will never have a situation that meets the standard definition of a time constant.  So in that sense there is no time constant.

Take the example of a car that is front wheel drive.  A car with front-wheel drive will not handle the same way as a car with rear-wheel drive.  So there is no point in talking about handling problems with rear-wheel drive cars to someone driving a front-wheel drive car.

And yes, the time constant is infinity.  It's another way of saying the same thing.  The real question is what does that mean for this test?

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #119 on: May 09, 2016, 08:48:51 PM »
Poynt, I hope you did not miss my reply #108.