MH's ideal coil and voltage question

[tinman]

Brad,



Now, replace the ideal inductor with an ideal discharged capacitor, what is the outcome at t=0?

Do you still think with the inductor scenario current instantly going to infinity is a possibility?

Yes, nothing will happen with the ideal inductor, i.e. it will have 4V (or whatever the voltage is at any point in time) across it and zero current through it for ever and ever. (You can't have both answers.)

Ok,in this point in time,i will provide my real world answer,along with my !two! theoretical answers.

My real world answer is(and has been throughout this thread)that you cannot place an ideal voltage across an ideal inductor,as an ideal inductor dose not -and never will exist.

Theoretical answer 1--> As R = 0,then the L/R time constant is infinite-as you have just stated is correct Poynt. The first thing this means is that the question asked by MH with the values given in that question,results in nothing at all happening--as you also just stated would be the situation.

What we now need to do to understand my second theoretical answer, is define the properties of an ideal inductor. An ideal inductor has no resistance or capacitance,but only inductance. This is now when we find out that the ideal inductor has no inductance at all-regardless of the inductance value of that ideal inductor. For inductance to occur,current must flow into that inductor,and as we have both just established,no current will into that inductor ,regardless of the voltage across that ideal inductor,or the time the voltage is across that inductor,as the current rise time is infinite,and there for there is an infinite time before current starts to flow-->there is no current flowing into that inductor-ever,as we know know.

As we have no capacitance value,then the voltage across the inductor is not stored across the inductor,so this is omitted. But what we do have,due to there being no resistance,is a dead short across the inductors terminals,which brings rise to my theoretical answer 2.

Theoretical answer 2-->. As it has now been concluded that there is no current flowing into the ideal inductor,then there is no inductance taking place. We are now left with an ideal voltage across a dead short,due to the zero value of resistance. This leads to an instant current rise to an infinite value due to the ideal voltage now being across a dead short. I will define instant being the ideal speed at which current can flow,that being the speed of light.

So you see now why i called this a conundrum theory.
But what these two theories prove,is my real world answer,and that is,as you know-->that you cannot place an ideal voltage across an ideal inductor,as an ideal inductor dose not -and never will exist.

There is also a second conundrum,and that being that we all agree that a voltage cannot exist across an ideal inductor that has a steady DC current flowing through it. If an ideal inductor,with an ideal voltage placed across it,never has current flowing into or through it,how did the steady state current get induced into the ideal inductor,that dose not allow a voltage to be seen across it?.

We have worked out that current will never flow into an ideal inductor,and now all we have to do is work out the rest of what i posted--or should i say Poynt,have your opinion toward what i have posted above.


Brad

[tinman]

Brad:

You have actually been given part of the answer, and you see that you were dead wrong.  Turn that into a learning experience.

These are the two challenges for you:

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.

I will repost my answer to the harder version of the question on this thread.

MileHigh

MH
Did you not see Poynts post (80)
Quote: Yes, nothing will happen with the ideal inductor, i.e. it will have 4V (or whatever the voltage is at any point in time) across it and zero current through it for ever and ever.

This in itself says that the results to your question will be-nothing happens. It also shows that one of my theoretical answers was correct,and my real world answer was also correct--when you read my last pots,you may start to understand the complications with your !original! question.

To quote your post 69-- Sorry but I have to lol, when the "answer" is two completely contradictory answers.,i think once again,you have laughed at me to soon.

Brad

[tinman]

Here is the harder version of the question and the answer:

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.  The voltage source waveform is 20*t^2.  So as the time t increases, the voltage increases proportional to the square of the time.

The question is what happens starting at t = 0

The answer:

The current through the ideal coil starts from zero at time t = 0 and then increases with this formula:  i = 1.33*t^3.

Time..........Voltage.........Current
0...............0.................0
1...............20...............1.33
5...............500.............166.67
10.............2000............1333.33
20.............8000............10666.67
50.............50000..........166666.7

Brad, you need to try to get up the learning curve such that you get to the point where you come back and acknowledge the answer given above is correct.

As i clearly stated MH,we are not resolving your modified version until your original question is answered.
Please stop trying to confuse people in this thread,that is dedicated to resolving your original question.


Brad

[tinman]

Here is the harder version of the question and the answer:



The question is what happens starting at t = 0

The answer:

The current through the ideal coil starts from zero at time t = 0 and then increases with this formula:  i = 1.33*t^3.

Time..........Voltage.........Current
0...............0.................0
1...............20...............1.33
5...............500.............166.67
10.............2000............1333.33
20.............8000............10666.67
50.............50000..........166666.7

Brad, you need to try to get up the learning curve such that you get to the point where you come back and acknowledge the answer given above is correct.

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.  The voltage source waveform is 20*t^2.  So as the time t increases, the voltage increases proportional to the square of the time.

If the voltage increases,then it is not an ideal voltage,as an ideal voltage dose not change in time.
Your original question clearly states an ideal voltage of 4 volts for 3 seconds.

The rest of your answer is not related to the original question,as the voltage is not 4 volts for 3 seconds.

https://en.wikipedia.org/wiki/Voltage_source
An ideal voltage source is a two-terminal device that maintains a fixed voltage drop across its terminals. It is often used as a mathematical abstraction that simplifies the analysis of real electric circuits.

Brad

[MileHigh]

Brad:

Re: Poynt's comment:

Yes, nothing will happen with the ideal inductor, i.e. it will have 4V (or whatever the voltage is at any point in time) across it and zero current through it for ever and ever.

I am not sure of the context for that or he may simply have been sarcastic.

What I can say to you is this:

The question was posed to you with an ideal inductor and you objected to that.  So I then reposed the question to you and added a resistor that gives you a time constant of 158,440 years and you agreed in principle that that variant of the question can be answered.  On top of that, you have already been given a partial correct answer.

So what you (or anyone else) need to do is try to answer either question, the original or the variant.  Both answers will essentially be the same.

So there is only one real answer, even if you use the variant question.  And the answer is still not forthcoming from you or from anyone else.  That means you have an opportunity to shine and demonstrate that you understand what is going on, you understand inductance, and you understand how an inductor works.

So forget about your long and complicated answer in post #91.  A simple question can be answered with a simple answer, and then also demonstrate your competence on the subject matter.  Give it your best shot.

MileHigh