Infinite Capacitance _ Capacitor Diagnosis

Thread Starter

ben sorenson

Joined Feb 28, 2022
180
Hello, I was wondering if a capacitor with infinite capacitance existed how could one diagnose it to verify that it actually infact did have "infinite" capacitance?
 

KL7AJ72

Joined Apr 15, 2021
22
Hello, I was wondering if a capacitor with infinite capacitance existed how could one diagnose it to verify that it actually infact did have "infinite" capacitance?
This would present an untenable paradox. We run across a similar situation when looking at the ionosphere when there's no propagation. Two exact opposite conditions can have the exact same result. No ionization= no ionosphere. Excessive ionization= total absorption. Same results...no radio propagation.
 

BobTPH

Joined Jun 5, 2013
8,664
I guess it would be indistinguishable from a zero Ohm resistor. You could keep putting current into (or through) either and it would never develop a voltage across it.
 
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Hymie

Joined Mar 30, 2018
1,272
The ac impedance of the capacitor would be zero; how accurately you could measure zero impedance would determine how accurately you would determine the capacitance to be infinite.
 

BobTPH

Joined Jun 5, 2013
8,664
Proposed final exam at Hogwart’s School of Electronics.

You have 3 black boxes with two terminals each. They contain:

1. An infinite Farad capacitor.
2. A zero Ohm resistor.
3. A zero Henry inductor.

Determine which is which by any means you think might work.
 

billnow

Joined Aug 4, 2010
23
Proposed final exam at Hogwart’s School of Electronics.

You have 3 black boxes with two terminals each. They contain:

1. An infinite Farad capacitor.
2. A zero Ohm resistor.
3. A zero Henry inductor.

Determine which is which by any means you think might work.
I would label all three as item "A" and then state that each item "A" is a perfect substitute for any other item "A".
 

Thread Starter

ben sorenson

Joined Feb 28, 2022
180
The ac impedance of the capacitor would be zero; how accurately you could measure zero impedance would determine how accurately you would determine the capacitance to be infinite.
What would be the most accurate way to measure for infinite capacitance?
 

ElectricSpidey

Joined Dec 2, 2017
2,756
Well, maybe all capacitors have infinite capacitance...think about it.

First a capacitor must fill with half of the charge, then fill half of the remaining capacity, then fill half of that remaining capacity...

;)
 

KL7AJ72

Joined Apr 15, 2021
22
There's a genuine mixed bag here. I'm never averse to telling my students "Infinity is a number too." It just needs to be used appropriately.
 

Ya’akov

Joined Jan 27, 2019
8,973
Proposed final exam at Hogwart’s School of Electronics.

You have 3 black boxes with two terminals each. They contain:

1. An infinite Farad capacitor.
2. A zero Ohm resistor.
3. A zero Henry inductor.

Determine which is which by any means you think might work.
Assuming they contain what they are labelled, no testing is required.

For boxes 1, 2, and 3:

  1. 1 is the capacitor, resistor, or inductor
  2. 2 is the capacitor, resistor, or inductor
  3. 3 is the capacitor, resistor, or inductor

The application of each is at the discretion of the user.
 

Hymie

Joined Mar 30, 2018
1,272
Hymie said:-

The ac impedance of the capacitor would be zero; how accurately you could measure zero impedance would determine how accurately you would determine the capacitance to be infinite.
What would be the most accurate way to measure for infinite capacitance?

The impedance (Z) of a capacitor (C) at a given frequency (f) is given by:-

Z = 1/(2 * π * f * C)

Therefore as C tends towards infinity, Z will tend towards zero; therefore the more accurately the ultra low value of Z can be determined, the greater the accuracy in determination of a very large capacitor value.
 

Ian0

Joined Aug 7, 2020
9,502
An infinite capacitor must have infinite plate area*, but it doesn't need infinite plate thickness, so the plates can have non-negligible resistance, which would also be infinite. Doesn't that turns it into some sort of lossy transmission line?

*I suppose it could have dielectric of infinitesimal thickness, but then it would have almost zero voltage rating.
 
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