MH's ideal coil and voltage question

[EMJunkie]

@All - Dont forget, Impedance has two different types of Resistance, Real and Imaginary.

Imaginary consists of Inductive Reactance and Capacitive Reactance - This is considered to be a Resistance also.

For DC, it does not apply unless youre looking at the rise and fall times as a Frequency Component. So youre pretty safe to say DC there is none.

However, at any frequency there will be a value of Impedance even if the Real Resistance is 0.

    Chris Sykes
        hyiq.org

see: https://www.researchgate.net/figure/237776087_fig9_Figure-9-Impedance-and-ESR-vs-Frequency-for-T520-vs-T528-equal-parts

P.S: Impedance (Z) and Equivalent Series Resistance (ESR) run the same race, they are parts of the samething. So, really, at any Frequency, there can be no Ideal Inductor with Zero Resistance. At least according to theory. Only at DC. Which some have already explained.

[verpies]

@All - Dont forget, Impedance has two different types of Resistance, Real and Imaginary.

To be technically correct it should've been written:

"Impedance has two different types of Ohms - Real and Imaginary"
OR
"Impedance has two different components - Real and Imaginary"

...because the word "Resistance" is reserved for the real component of Impedance.

This is just a terminological correction - not a conceptual one.

[EMJunkie]

To be technically correct it should've been written:

"Impedance has two different types of Ohms - Real and Imaginary"
OR
"Impedance has two different components - Real and Imaginary"

...because the word "Resistance" is reserved for the real component of Impedance.

This is just a terminological correction - not a conceptual one.

Yes, of course, thanks Verpies, both are measured in Ohms: Ω-jΩ or Ω+jΩ

If you see something like:

   Z = 10-j10 (-j = Inductive Reactance)
or
   Z = 10+j10 (+j = Capacitive Reactance)

This is where 10 Ohms of Real Resistance and 10 Ohms of Reactance: (X_L Reactive Iductance or X_C Reactive Capacitive).

See: http://www.saylor.org/site/wp-content/uploads/2011/07/ME301-vol-2.pdf

http://www.allaboutcircuits.com/textbook/alternating-current/chpt-4/series-resistor-capacitor-circuits/

    Chris Sykes
        hyiq.org

[tinman]

Otherwise, I agree with the above statement.  Not only an ideal inductor is devoid of an asymptotic V/R current limit but also the current through an inductor of infinite inductance, that is somehow connected to an ideal voltage source, could never change because of the implied zero di/dt at any voltage.

Of course, it is debatable whether an ideal inductor must have an infinite inductance.  Some would say that it is enough for it to have zero resistance and zero parasitic capacitance.

However it is possible to externally change the magnetic flux penetrating a shorted ideal inductor. Doing so will instantaneously cause a current to circulate through it ^*, in order to maintain the previous flux level penetrating its windings.  This is a voltageless current! - it cannot be measured by a voltmeter and it was not caused by a voltage source.

Last but not least - inductors are current devices and voltage creates no effects in them.  Voltage cannot even be measured in shorted ideal inductors (neither practically nor theoretically!). Measurement of voltage (emf) is meaningful only for non-ideal inductors (e.g. open inductors or inductors with series resistances).  Open inductors or inductors without current flowing though them are dummy inductors - they create no effects on the environment.  Voltmeter deflection notwithstanding.

P.S.
I'm just replying to Tinman's post and I have not read what others wrote in this thread.


^* (without delay and regardless of its inductance)

Since an ideal inductor must have a zero resistance, this means that it must be shorted (if it ain't shorted, it ain't ideal) and it becomes physically impossible to connect any real voltage sources in series with it.

Thank you verpies for joining in on this discussion.
You have confirmed my real world answer--an ideal voltage cannot be applied to/placed across an ideal inductor.

Last but not least - inductors are current devices and voltage creates no effects in them.  Voltage cannot even be measured in shorted ideal inductors (neither practically nor theoretically!). Measurement of voltage (emf) is meaningful only for non-ideal inductors (e.g. open inductors or inductors with series resistances).  Open inductors or inductors without current flowing though them are dummy inductors - they create no effects on the environment.  Voltmeter deflection notwithstanding.

I only hope Poynt reads what both you and i have stated,and revisits his thoughts on the question presented by MH,and understands that the math MH is using to make his calculations do not apply when dealing with ideal inductor's.

Just another proof that placing a voltage across an ideal inductor dose not create a current flow through that ideal inductor.

Being an ideal inductor,means that it dose not dissipate power,and that also means the CEMF is also ideal,--> equal to that which creates it,and thus no current flows when a voltage is placed across that ideal inductor.

A non ideal inductor dose have an R value,and this means it dose dissipate power. This also means that the CEMF value is not as high as the EMF that created it,and so current will flow through a non ideal inductor--as we know.


Brad

[tinman]

To be technically correct it should've been written:

"Impedance has two different types of Ohms - Real and Imaginary"
OR
"Impedance has two different components - Real and Imaginary"

...because the word "Resistance" is reserved for the real component of Impedance.

This is just a terminological correction - not a conceptual one.

Verpies
Would you care to answer the question below,and give the reason for your 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. 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?.

Brad