A 'Leyden Jar' Capacitor, with a difference?? - Page 1
Forum section: electronics / general

author: GlennSprigg
author_rank: Super Contributor
timestamp: January 10, 2021, 01:15:26 pm
content: We here all do/should know about the ubiquitous 'Leyden Jar', as described in...https://en.wikipedia.org/wiki/Leyden_jarHowever, I just watched an old youtube video with Professor Julius Sumner Miller, where he demonstrated a physicalconstruction of one, using 2 aluminium cans and a glass jar stacked together. OK, that sounds good... He then chargedone 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 themetal parts together, before re-assembling it all with the glass jar. He then demonstrated by connecting the 2 metal partswith a spark,that the 'charge' was still there??!! He has a habit of leaving 'experiments' for people to work out why, bythemselves!... It has me confused. Actually, his whole video is interesting, but the point I mention starts here...https://youtu.be/4wa8IKMYwK8?t=358

author: Gyro
author_rank: Super Contributor
timestamp: January 10, 2021, 02:40:09 pm
content: Are you asking for the answer?

author: wraper
author_rank: Unknown
timestamp: January 10, 2021, 03:29:24 pm
content: Quotehttps://en.wikipedia.org/wiki/Leyden_jar

author: GlennSprigg
author_rank: Super Contributor
timestamp: January 12, 2021, 12:20:16 pm
content: Quote from: Gyro on January 10, 2021, 02:40:09 pmSorry 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 generalconsensus. I did actually have my own ideas, (before reading that myself), that if this 'magical' charge is no longerin the metal components, then the only thing left is the Dielectric! ?? Didn't seem right, but I further imagined thatI 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 thefictionalSherlock Holmes who purportedly said... "When you have eliminated the impossible, whatever remains, howeverimprobable, must be the truth". Maybe these words from the Author, (Arthur Conan Doyle) are wize!!!

author: Gyro
author_rank: Super Contributor
timestamp: January 12, 2021, 12:41:19 pm
content: 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

author: GlennSprigg
author_rank: Super Contributor
timestamp: January 12, 2021, 01:22:29 pm
content: Thank You...