MH's ideal coil and voltage question

[tinman]

I've attached an LtSpice sim of a 5 henry inductor with a dc resistance of 1e-11 connected to a 4 volt ideal voltage source for 3 secs.

At the end of three secs we see the inductor current has reached 2.4 amps.  This is as close to a perfect inductor as one could want.

Using the formula that MH supplied that is, delta I = Et/L, this results in delta I = 4*3/5 = 2.4 amps.

What happens if we increase the dc resistance to a higher resistance? The peak current reached will simply be lower than the above depending on the value of the resistance under otherwise the same conditions.

partzman

Unfortunately partzman,it is no where near an ideal inductors outcome,as an ideal inductor never has any current passing through it.


Brad

[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 across it and zero current through it for ever and ever. (You can't have both answers.)

Well this as you know,was one of my answers. My other answer is because there is no resistance with an ideal inductor,and there for it is a dead short.

Your self,verpies,MH and ION have all stated that there is no voltage across an ideal inductor that has a steady DC current flowing through it. So if it is as you say-nothing will happen when an ideal voltage is placed across an ideal inductor--no current will flow,how can you then say that no voltage will be across an ideal inductor when there is a DC current flowing through it. How did the current flow take place if no current flow will take place when the ideal voltage was placed across it?.


In regards to the ideal capacitor,would we not have the same conundrum?


Brad

[MileHigh]

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

[MileHigh]

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.

[MileHigh]

I've attached an LtSpice sim of a 5 henry inductor with a dc resistance of 1e-11 connected to a 4 volt ideal voltage source for 3 secs.

At the end of three secs we see the inductor current has reached 2.4 amps.  This is as close to a perfect inductor as one could want.

Using the formula that MH supplied that is, delta I = Et/L, this results in delta I = 4*3/5 = 2.4 amps.

What happens if we increase the dc resistance to a higher resistance? The peak current reached will simply be lower than the above depending on the value of the resistance under otherwise the same conditions.

partzman

Thank you partzman for running the simulation.  I am hoping that this gives Brad and others enough information to answer the full question and demonstrate that they understand the concepts and show competence in the subject matter.  In that sense please refrain from providing further answers to the complete question that defines a multi-part voltage waveform.  The hope is that the interested parties undertake to teach themselves as apposed to being spoon fed the answers.

MileHigh