### Author Topic: A 'Leyden Jar' Capacitor, with a difference??  (Read 535 times)

0 Members and 1 Guest are viewing this topic.

#### GlennSprigg

• Frequent Contributor
• Posts: 979
• Country:
• Medically retired Tech. Old School / re-learning !
##### A 'Leyden Jar' Capacitor, with a difference??
« on: January 10, 2021, 01:15:26 pm »
We here all do/should know about the ubiquitous 'Leyden Jar', as described in...
https://en.wikipedia.org/wiki/Leyden_jar

However, I just watched an old youtube video with Professor Julius Sumner Miller, where he demonstrated a physical
construction of one, using 2 aluminium cans and a glass jar stacked together. OK, that sounds good... He then charged
one of the 'plates' with high voltage, and demonstrated a strong discharge spark between the 2 metal components. OK.

He then repeated this, but before discharging it, he pulled it all apart, and 'grounded' all the parts, including touching the
metal parts together, before re-assembling it all with the glass jar. He then demonstrated by connecting the 2 metal parts
with a spark,that the 'charge' was still there??!!  He has a habit of leaving 'experiments' for people to work out why, by
themselves!... It has me confused. Actually, his whole video is interesting, but the point I mention starts here...

https://youtu.be/4wa8IKMYwK8?t=358
Diagonal of 1x1 square = Root-2. Ok.
Diagonal of 1x1x1 cube = Root-3 !!!  Beautiful !!

#### Gyro

• Super Contributor
• Posts: 6162
• Country:
##### Re: A 'Leyden Jar' Capacitor, with a difference??
« Reply #1 on: January 10, 2021, 02:40:09 pm »
Chris

"Victor Meldrew, the Crimson Avenger!"

The following users thanked this post: GlennSprigg

#### wraper

• Supporter
• Posts: 12652
• Country:
##### Re: A 'Leyden Jar' Capacitor, with a difference??
« Reply #2 on: January 10, 2021, 03:29:24 pm »
Quote
This demonstration appears to suggest that capacitors store their charge inside their dielectric. This theory was taught throughout the 1800s. However, this phenomenon is a special effect caused by the high voltage on the Leyden jar. In the dissectible Leyden jar, charge is transferred to the surface of the glass cup by corona discharge when the jar is disassembled; this is the source of the residual charge after the jar is reassembled. Handling the cup while disassembled does not provide enough contact to remove all the surface charge. Soda glass is hygroscopic and forms a partially conductive coating on its surface, which holds the charge. Addenbrooke (1922) found that in a dissectible jar made of paraffin wax, or glass baked to remove moisture, the charge remained on the metal plates. Zeleny (1944) confirmed these results and observed the corona charge transfer.
https://en.wikipedia.org/wiki/Leyden_jar

The following users thanked this post: nctnico, GlennSprigg

#### GlennSprigg

• Frequent Contributor
• Posts: 979
• Country:
• Medically retired Tech. Old School / re-learning !
##### Re: A 'Leyden Jar' Capacitor, with a difference??
« Reply #3 on: January 12, 2021, 12:20:16 pm »

Sorry for any ambiguity mate. Not really requesting an answer as such, but was more a "Food for Thought"
It seems that many people have varying opinions about what is/may be going on. 'wraper' did hit on the general
consensus.  I did actually have my own ideas, (before reading that myself), that if this 'magical' charge is no longer
in the metal components, then the only thing left is the Dielectric! ??  Didn't seem right, but I further imagined that
I can't imagine that working if the 'dielectric' was say air, or a vacuum, so it must require a SOLID Dielectric !...

I still hadn't worked out exactly how though prior to that, but I was reminded of a statement by the fictional
Sherlock Holmes  who purportedly said... "When you have eliminated the impossible, whatever remains, however
improbable, must be the truth
".  Maybe these words from the Author, (Arthur Conan Doyle) are wize!!!
Diagonal of 1x1 square = Root-2. Ok.
Diagonal of 1x1x1 cube = Root-3 !!!  Beautiful !!

#### Gyro

• Super Contributor
• Posts: 6162
• Country:
##### Re: A 'Leyden Jar' Capacitor, with a difference??
« Reply #4 on: January 12, 2021, 12:41:19 pm »
Yes, you're right, this demonstration can only apply to solid dielectrics. With air and vacuum capacitors, the charge is held on the electrodes themselves. I doubt you would see a capacitance change in an air dielectric capacitor exposed to air movement (although I've never tried it). With vacuum capacitors, there is no dielectric to isolate anyway.

No doubt there would have been some very small charge on the metal cans in the demonstration, but far too low to perceive and completely swamped by the magnitude of the charge stored in the solid dielectric jar.

I guess the best demonstration of charge with a non-solid dielectric [Edit: No dielectric] was the repeated precautionary grounding of the dome on the Van De Graaff generator.

P.S. The original  Electrophorus is a useful demonstration of building up a charge in a solid dielectric without having an electrode (and then transferring it to an isolated metallic electrode)   https://en.wikipedia.org/wiki/Electrophorus
« Last Edit: January 12, 2021, 12:55:29 pm by Gyro »
Chris

"Victor Meldrew, the Crimson Avenger!"

The following users thanked this post: GlennSprigg

#### GlennSprigg

• Frequent Contributor
• Posts: 979
• Country:
• Medically retired Tech. Old School / re-learning !
##### Re: A 'Leyden Jar' Capacitor, with a difference??
« Reply #5 on: January 12, 2021, 01:22:29 pm »
Thank You...
Diagonal of 1x1 square = Root-2. Ok.
Diagonal of 1x1x1 cube = Root-3 !!!  Beautiful !!

Smf