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### Author Topic: MH's ideal coil and voltage question  (Read 412801 times)

#### tinman

• Hero Member
• Posts: 5242
##### MH's ideal coil and voltage question
« on: May 08, 2016, 10:42:41 AM »
I have started this thread to solve MileHighs question below.
Please keep the insults down,and the language clean.

MH's question.

You have an ideal voltage source and an ideal coil of 5 Henrys.  At time t=0 seconds the coil connects to the ideal voltage source. For three seconds the voltage is 4 volts.  Then for the next two seconds the voltage is zero volts. Then for two seconds the voltage is negative three volts, and then for the next six seconds the voltage is 0.5 volts.  Then after that the voltage is zero volts.
What happens from T=0 when the ideal voltage is connected to the ideal coil?.

My answer to this question is--you cannot place an ideal voltage across an ideal inductor.
The reason being,at T=0,when the ideal voltage is placed across the ideal inductor,the current would rise instantly to a value of infinity. The reason this cannot happen,is because an ideal inductor dose not dissipate any power in the form of heat,due to the fact that it has no resistance or hysteresis loss,as it is an ideal inductor. If an ideal voltage was placed across an ideal inductor(in theory),it would result in an explosion the likes the universe has not seen since the creation of it-the big bang all over again.

All are welcome to have a go at answering MHs question.

MH

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #1 on: May 08, 2016, 01:00:32 PM »

You are one strange egg Brad because you think you are "running the show" now but in fact the show is running you.

Re: This posting from the other thread:  http://overunity.com/8341/joule-thief-101/msg483350/#msg483350

As I already stated, you make reference to an "R" resistance but there is none in the example being discussed.  You also make reference to a divide-by-zero for a time constant and state that it is "instantaneous" when it is infinity or undefined.  You are told these two things are wrong in a later posting but like the Pope you pretend that you are infallible and can just "waive" past these two glaring errors because you are Brad.

Re: This posting from the other thread:  http://overunity.com/8341/joule-thief-101/msg483376/#msg483376

You are all in a tizzy because I mention a "'trick' question."  But unfortunately you have another case of crossed signals in your head.  It's not my question in that posting that is the "trick," it's actually ION's follow-up question to my question that is the "trick."  I say in jest to ION that his question is a "trick" question but that flies right over your head.  Lo and behold, the signals get crossed in your head and you accuse me of asking a "trick" question when I did no such thing.

But the most mind-blowing thing about that posting of yours is that you completely gloss over the extremely important and relevant technical information that is contained in that posting.

For me, there are only two outstanding issues and I will mention them again and I will put them in a better sequence this time:

1.  Brad gets up the learning curve and understands the original question and then answers it correctly all by himself and clearly demonstrates that he understands what he is doing.
2.  Brad admits that he is wrong when he stated that my response to the harder question is wrong.

You are stating that you want to try to answer the question.  That's a good thing and your first try is wrong, good luck.

MileHigh

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #2 on: May 08, 2016, 02:26:08 PM »

MileHigh

Quote

OK
If my answer is wrong,then it is now up to you to prove that by supplying the correct answer.
I have given my answer to your question,and you cannot just say it's wrong without being able to support that claim by supplying what you believe to be the correct answer.
We are only discussing the original question here ATM.

Quote
As I already stated, you make reference to an "R" resistance but there is none in the example being discussed.

MH
My reference to resistance is a value of 0 ohms.
Is not 0 ohms resistance no resistance? Your statement makes no sense ,as i do not state any resistance ,as 0 is none. I only say that,so as others reading the question understand that an ideal coil has 0 ohms of resistance--no resistance.

Quote
You are one strange egg Brad because you think you are "running the show" now but in fact the show is running you.

I am providing an answer to your question,and now you have to disprove my answer by way of supplying the one you think is correct.

Quote
You also make reference to a divide-by-zero for a time constant and state that it is "instantaneous" when it is infinity or undefined.  You are told these two things are wrong in a later posting but like the Pope you pretend that you are infallible and can just "waive" past these two glaring errors because you are Brad.

I am told i am wrong by who MH?

Quote
You are all in a tizzy because I mention a "'trick' question."  But unfortunately you have another case of crossed signals in your head.  It's not my question in that posting that is the "trick," it's actually ION's follow-up question to my question that is the "trick."  I say in jest to ION that his question is a "trick" question but that flies right over your head.  Lo and behold, the signals get crossed in your head and you accuse me of asking a "trick" question when I did no such thing.

OK,so lets say that your question above is not a !trick! question as i have stated.
So now i will ask you (as you think i have it wrong)to calculate the time from T=0 in your question,it takes the ideal inductor to reach it's maximum current flow value,once the ideal voltage of 4 volts is placed across that coil.

Quote
But the most mind-blowing thing about that posting of yours is that you completely gloss over the extremely important and relevant technical information that is contained in that posting.

You mean IONs response to your question?,once again referring to an ideal voltage from an ideal power supply,being placed over an ideal inductor?.
Well let's leave ION out of this for a while,and let you answer the questions,as it is your question we are talking about here,and so you are the one that should be providing the required answers.

Quote
For me, there are only two outstanding issues and I will mention them again and I will put them in a better sequence this time:

1.  Brad gets up the learning curve and understands the original question and then answers it correctly all by himself and clearly demonstrates that he understands what he is doing.

Quote
2.  Brad admits that he is wrong when he stated that my response to the harder question is wrong.

We are discussing your original question above only, in this thread at the moment.

Quote
You are stating that you want to try to answer the question.  That's a good thing and your first try is wrong, good luck.

Regarding the question we are discussing in this thread(your original question to EMJ and Wattsup),i have answered the question correctly. If you believe i am wrong,then you must provide the evidence to show that.

So the questions i have for you MH are
1-how is the current time constant calculated for your ideal inductor/
2-What is the time taken for the current to rise to peak value from T=0,that moment when the ideal voltage of 4 volts is placed across the ideal inductor?.

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #3 on: May 08, 2016, 02:58:48 PM »
If there is no resistor in the schematic then you do not discuss an imaginary zero-ohm resistor that you want to force into the schematic.  It's a non-starter.

I told you Brad to try to work it out with your peers or work it out by yourself.  I am not going to supply you with the correct answer.  If I did that you would balk anyway and fight over it for 100 postings.  I am not doing that.

"You are wrong."
"Okay, now give me the right answer."

It's not going to work like that.

You should say, "Okay, I will discuss it with my peers and go do more research and learn more and improve my skills so that I can answer the question successfully by myself."

You clearly have no understanding at all about how an inductor actually works.  That is the essence of the question.  Why don't you start there?

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #4 on: May 08, 2016, 03:17:54 PM »
Stop trolling Webby.  Don't ruin a brand new thread.

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #5 on: May 08, 2016, 03:21:01 PM »
If there is no resistor in the schematic then you do not discuss an imaginary zero-ohm resistor that you want to force into the schematic.  It's a non-starter.

I told you Brad to try to work it out with your peers or work it out by yourself.  I am not going to supply you with the correct answer.  If I did that you would balk anyway and fight over it for 100 postings.  I am not doing that.

"You are wrong."
"Okay, now give me the right answer."

It's not not going to work like that.

."

You clearly have no understanding at all about how an inductor actually works.  That is the essence of the question.  Why don't you start there?

So you are not here to debate or discuss your question,but only to leave it to me to do all the work.
So much for you insisting on debating things

Quote
You should say, "Okay, I will discuss it with my peers and go do more research and learn more and improve my skills so that I can answer the question successfully by myself

My skills are fine thank you MH.
My answer to your question above is correct,and as you have provided no answer other than to say mine is incorrect,we can safely say your answer is incorrect,as i believe mine is correct,and you disagree with my answer.

As you have not provided any proof that my answer is incorrect,nor have you attempted to answer a couple of simple questions,we can assume that you cannot answer them,nor can you provide evidence that my answer is incorrect.

So as you do not wish to be a part of this debate,or help others find the answer to your question,i will post some answers for you.

Q1-can a voltage exist across an ideal inductor that has a DC current flowing through it.
Your answer MH (if you know your stuff)will be no,a voltage cannot exist across an ideal inductor that has a DC current flowing through it.
Have you ticked this box in the pole question?--seems not.

So now that you agree that a voltage cannot exist across an ideal inductor that has a DC current flowing through it,how can you have a voltage of 4 volts existing across an ideal inductor for 3 second's--an inductor that has no resistance?.

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #6 on: May 08, 2016, 03:43:17 PM »
<<< no,a voltage cannot exist across an ideal inductor that has a DC current flowing through it. >>>

And that's probably the only thing that you have stated about this subject so far that is correct.

I will repeat to you:  I already answered a variation on the question that is actually more difficult to answer.  I gave a complete and full answer.  It's up to you and your peers to try to answer the simpler question if you want to.

I am just waiting and hoping for a successful conclusion.  I will repeat:  You clearly have no understanding at all about how an inductor actually works.  That is the essence of the question.  Why don't you start there?

If you don't get a guru parachuting in to help you and you and your peers are unable to answer a question about one of the simplest circuits possible, so be it.

These are the only two things I am interested in hopefully seeing a successful resolution to:

1.  Brad gets up the learning curve and understands the original question and then answers it correctly all by himself and clearly demonstrates that he understands what he is doing.
2.  Brad admits that he is wrong when he stated that my response to the harder question is wrong.

MileHigh

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #7 on: May 08, 2016, 04:22:24 PM »
<<< no,a voltage cannot exist across an ideal inductor that has a DC current flowing through it. >>>

And that's probably the only thing that you have stated about this subject so far that is correct.

I will repeat to you:  I already answered a variation on the question that is actually more difficult to answer.  I gave a complete and full answer.  It's up to you and your peers to try to answer the simpler question if you want to.

I am just waiting and hoping for a successful conclusion.  I will repeat:  You clearly have no understanding at all about how an inductor actually works.  That is the essence of the question.  Why don't you start there?

If you don't get a guru parachuting in to help you and you and your peers are unable to answer a question about one of the simplest circuits possible, so be it.

These are the only two things I am interested in hopefully seeing a successful resolution to:

1.  Brad gets up the learning curve and understands the original question and then answers it correctly all by himself and clearly demonstrates that he understands what he is doing.
2.  Brad admits that he is wrong when he stated that my response to the harder question is wrong.

MileHigh

MH
I would suggest at this point in time,you review your question,and not treat your inductor as a normal inductor that !dose! have a series/parallel resistance.
You clearly defined the inductor and voltage as being !ideal!.
You said your question was not a trick question,so i think you need to go and calculate the L/R time constant for your ideal inductor--some how
Once you have that L/R time constant value,we then only need multiply that by 5 to get a close approximation  for the time it takes that 5 henry ideal inductor to reach it's steady state current value after T=0-->the ideal voltage is applied across the ideal inductor.

All i ask is that you calculate the L/R time constant of your 5 henry ideal inductor.

How are you to work out the L/R time constant when there is no R

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #8 on: May 08, 2016, 04:24:50 PM »
MH,

does the question ask for when T=0

It does not start when T>0 the question is for when T=0

T=0 is the start of the cycle --> the instant the ideal voltage is placed across the ideal inductor

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #9 on: May 08, 2016, 04:43:36 PM »
You are lost Brad and you should take my advice and start from scratch.  And like usual you are completely baffling because some big clues were presented to you and they passed right through you like you weren't even there.  I am giving you a 10% chance to get it right.

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #10 on: May 08, 2016, 04:43:50 PM »
A post from Magneticitist on the JT 101 thread

What I find curious about the whole 'Ideal' scenario no matter how useful it may be in real world applications.. An Ideal inductor is said to dissipate or radiate 0 energy, so technically it only passes current by putting faith in Ohms law's ability to handle the number 0.

I would think that in an ideal voltage source, connecting to an ideal inductor, nothing at all would happen because the voltage cannot waver, and the lack of resistance in the inductor would cause an infinite current were it not for an ideal inductor being unable to dissipate energy. If it cannot dissipate energy it perfectly contains on faith, we cannot possibly observe this energy and it might as well be at rest with no charge.

So even in the fantasy realm of imaginary voltage sources and coils that are ideal, an inductor can do no work unless it actually becomes something we cannot call 'ideal'. further evidence against this paradox of passing infinite current at 0 resistance.

MHs response to some one posting there thought's--and good ones at that.

I am just letting you know as a courtesy that you clearly have no idea what you are talking about.

So now myself,EMJ,Wattsup and Magneticitist are wrong,and MH is yet to post an answer to his own question,nor seems that he is willing to provide any information or answers to other simple questions asked of him.

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #11 on: May 08, 2016, 05:00:39 PM »
You are lost Brad and you should take my advice and start from scratch.  And like usual you are completely baffling because some big clues were presented to you and they passed right through you like you weren't even there.  I am giving you a 10% chance to get it right.

Quote:
The time constant τ is an indicator of how long current takes to increase from zero to its steady-state value.
Here is a useful rule of thumb:
For most practical purposes, we may assume that all quantities in a DC RL circuit have reached their steady-state values after five time constants.

So if a circuit has a time constant of 1 millisecond, then it will take about 5 milliseconds for the circuit's currents and voltages to reach their steady-state values.
Since one time constant is equal to L÷R, we can write this rule of thumb as an equation:
Time to reach steady state ≈ 5×L÷R

So MH,if your !very large! 5 henry coil had a resistance value of say 5 ohms,then it would take 1 second to reach it's time constant,and 5 seconds to reach a steady state current flow.

If your 5 henry coil had just .0001 ohms resistance,then it would take 50,000 seconds to reach it's time constant,and 250,000 seconds to reach a steady state of current flow.

As your coil is ideal,it has no resistance.
So i ask again--how are you going to calculate the time constant of your ideal coil>?

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #12 on: May 08, 2016, 05:10:15 PM »
The answer is that there is no time constant.   A variation on the same question was already answered.

That's it, from this point on you can moan and groan and whine and complain all you want.  A better scenario is you tasking yourself with this:

1.  Brad gets up the learning curve and understands the original question and then answers it correctly all by himself and clearly demonstrates that he understands what he is doing.

If you try and make a good sincere effort of it but don't get there, then good show.  If you get there then great show.  But if you just whine for an answer and sit on your fanny and complain then you are going to have to hope that a guru comes along and spoon feeds you.  But of course if you are spoon fed then chances are in two weeks you will be a blank slate.

It's up to you.

• Hero Member
• Posts: 1317
##### Re: MH's ideal coil and voltage question
« Reply #13 on: May 08, 2016, 06:19:55 PM »
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

#### Magneticitist

• Full Member
• Posts: 131
##### Re: MH's ideal coil and voltage question
« Reply #14 on: May 08, 2016, 06:30:47 PM »
@AllCanadian   seems a reasonable deduction that follows logic. welcome to the club of having no idea.