ABOUT INFINITE INDUCTANCE, ZERO CAPACITANCE!

Thread Starter

b.shahvir

Joined Jan 6, 2009
457
Thanx for your clarifications, very much grateful. :)

Actually, while 'researching' this topic on my own, i created a mental picture in my mind about the behavior of a conductor/s which is assumed to possess 'zero' capacitance. I assumed a finite DC voltage source which is connected to two undefined conductors, seperated by an undefined distance and placed in a medium of 'zero' permittivity to facilitate 'zero' capacitance.

Now, no charge is acquired by either conductors, but they are at a finite voltage as dictated by the finite voltage source. Now I start shifting my assumptions from the 'ideal' to the 'real' world. Hence, now slowly but steadily, I assume the medium to possess finite permittivity and hence capacitance and eventually the conductors start acquiring +ve and -ve charges.....an electric field then gets established between the respective conductors of opposite polarity, giving rise to the conditions mentioned earlier.
I humbly request you to give your valuable comments on the same. :)

P.S. I'm still finding it difficult to visualize an ideal inductor with 'zero' reluctance in a similar manner though! :(
 

Skeebopstop

Joined Jan 9, 2009
358
Hi Friends, :)

CASE 1 :- Infinite Inductance

Let us consider an 'ideal' solenoid coil (zero resistance, pure inductance). It is connected to an AC supply of say, 220VAC, 50Hz. Now assume that the medium (or magnetic core) surrounding the coil presents 'zero' reluctance to the magnetic flux. Hence, the magnetic flux embracing the coil will be 'infinite'. This would result in an infinite inductance and hence, an infinite inductive reactance! Now, under these conditions, ideally, the current thru the coil must be 'zero'.

The problem is, it is pretty difficult to visualize this situation, as even to create an infinite magnetic flux, some finite amount of magnetizing current must flow thru the coil. But, as per the theoretical concept, infinite inductance means current thru the coil should be an absolute zero! This cannot be realized even by examining the voltage versus current waveform of a pure inductor where current lags supply voltage by 90 deg. Hence, plz help!

Shahvir
I can't be bothered to get up to speed on this post but I just wanted to add my two cents to your original query of infinite inductance.

1. The H field is induced and independant of Flux or medium, but dependant only on the charge flow in the coil.
2. Flux is derived from H depending on the medium.

2 cannot happen without 1.

0 Magnetic reluctance means that 1 and 2 happen at the same time and that there are infinite 'free' electrons which 'align' to the H field without any work/effort (obviously not a real situation in our physical universe). Furthermore, it must happen instantaneously and faster than the current flows in order to ensure '0' current during activation. This situation must hold 'continuously', such that free electrons are constantly being re-aligned in order to induce a back-emf equal and opposite to the incoming one. Basically, an inductor which stores no energy and never saturates.....

This is obviously against all principles of electromagnetism and your way of viewing it cannot be described using modern physics.

Create some new equations to describe your situation maybe? :)

Maybe someday you'll get the nobel prize when somebody figures a way to empirically prove it.
 

Thread Starter

b.shahvir

Joined Jan 6, 2009
457
Thanx for your clarifications, very much grateful. :)

Actually, while 'researching' this topic on my own, i created a mental picture in my mind about the behavior of a conductor/s which is assumed to possess 'zero' capacitance. I assumed a finite DC voltage source which is connected to two undefined conductors, seperated by an undefined distance and placed in a medium of 'zero' permittivity to facilitate 'zero' capacitance.

Now, no charge is acquired by either conductors, but they are at a finite voltage as dictated by the finite voltage source. Now I start shifting my assumptions from the 'ideal' to the 'real' world. Hence, now slowly but steadily, I assume the medium to possess finite permittivity and hence capacitance and eventually the conductors start acquiring +ve and -ve charges.....an electric field then gets established between the respective conductors of opposite polarity, giving rise to the conditions mentioned earlier.
I humbly request you to give your valuable comments on the same. :)

I did be grateful if someone could give valuable comments on the same. :)

Thanks & regards,
Shahvir
 

Skeebopstop

Joined Jan 9, 2009
358
I did be grateful if someone could give valuable comments on the same. :)

Thanks & regards,
Shahvir
1. The permittivity of even a vacuum is not 0.
2. Given a finite voltage, regardless of permittivity, there is charge across the two wires/bars.

A capacitor can just be thought of as a 'tank' for differential equations. If you cease to have any capacitance the RC time constant of any first order differential model becomes 0. Thus your differential equations breaks down into:

RC(dV(t)/dt) + V(t) = f(t) => V(t) = f(t).

Your voltage is purely dependant on your forcing function (i.e. current or what have you). I feel this intuitive enough. Differential equations exists as models and you are trying to break the model by enforcing a non-realistic term, and as such, you are unable to use the same differential model to describe your system.

If you apply the model, as you see, the function becomes very simple. V(t) = f(t).
 

Thread Starter

b.shahvir

Joined Jan 6, 2009
457
Thanx for your reply :)
Actually, i am used to considering 'charged' conductors as those possessing negative and positive polarities. In puritical terms, that would mean a negatively charged conductor possessing 'excess' electrons and positively charged conductor the 'lack' of it!

Hence, Thingmaker's model of charged conductors without the 'excess' and 'deficit' of either charged particles was a bit hard for me to digest!

Refer:-
You can't put charge on a zero Farad capacitor, because you can't move it there. The charge stays at the source. Paradoxically, (thanks to this whole "zero" notion) the poles of the source are simultaneously the plates of the "Faradless capacitor" so the charge does not have to move in order for the "capacitor" to be "charged." Thus it is has zero charge time.
So, if the charge cannot be moved and stays at source, there can be no 'excess' or 'deficit' of charged particles (electrons) and hence, the concept of charged conductors becomes a bit sketchy to understand even if one does consider conductor/s possessing 'zero capaitance' (Faradless conductor/s).

I do not dispute the explanations presented.... but just for the sake of general discussion. :)

Kind regards,
Shahvir
 
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Skeebopstop

Joined Jan 9, 2009
358
Quantum mechanics are too hard to visualize sometimes.

Differential equations are used to describe electronic models and as such, the mathematics provides a very intuitive explanation.
 

thingmaker3

Joined May 16, 2005
5,083
So, if the charge cannot be moved and stays at source, there can be no 'excess' or 'deficit' of charged particles (electrons) and hence, the concept of charged conductors becomes a bit sketchy to understand even if one does consider conductor/s possessing 'zero capaitance' (Faradless conductor/s).
You've moved over into electrostatics.;)
 
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