Debugging a Kelvin Water Dropper

  • #1
Silloky
3
0
Homework Statement
For a high school project, I have to build a Leyden jar, ideally functional...

So to charge it, I'm trying to build a Kelvin Water Dropper. After 2 weeks of trying, and it being due on Monday, I can only come on here and hope some bright minds can help me troubleshoot it 😉.

Please note this is a copy of this question : https://physics.stackexchange.com/questions/832948/debugging-a-kelvin-water-dropper on Stack Exchange, but it was closed because it's homework...
Relevant Equations
None, really...
Here is the annoying machine :

kelvin.jpg


I'll just detail certain parts that I'm sure you're going to comment about !

* The inductors aren't touching the wood, there's some insulating foam (about $7mm$ in width once squished)
* The water stream breaks into droplets at about half of the inductor
* The jars in the bottom are glass, so insulating, and inside there are some copper coils.
* The 2 opposite-charge wires are fairly spaced (about $3cm$)

And when the water is flowing, no charge builds up, as the electroscope (the jar at the front of the photo), doesn't show any evidence whatsoever of charge on that system...
The electroscope works, attaching a coil to it and waving a previously-rubbed piece of polystyrene does make the aluminium flaps repel.

Also, I read humidity could be a problem, so I gave one system a little initial "boost" using the piece of polystyrene, to attract certain ions (not quite sure about the charge of polystyrene...).

I've tried using the electroscope and this charged polystyrene in a "circuit" to see if charges were leaving.
I found out :
1. if I wave the polystyrene on the coil attached directly to the electroscope, it works
2. if I wave the polystyrene next to the inductor connected to the electroscope, but not the empty containers, it works, but only if the electroscope coil isn't connected (I'm guessing the coil is doing the opposite job, giving up its charges to the air)
3. if I do wave the polystyrene in any of those 2 positions, but with the coil-activated containers connected, nothing happens (again, probably because the coil is inducing the air)
4. the 3rd test doesn't work either if the containers are full of regular (so, non-ionized) water

Do you have any ideas what I could be missing ?
The YouTube videos about this machine seem so simple, and yet, I'm still spending too much time on this thing...
 
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  • #2
Test the insulation. Disconnect the wires. Charge a balloon by rubbing it against hair or wool. Connect the electroscope to inductor 1, and try to charge the inductor with the charged balloon. If the electroscope leafs do not rise, the inductor is not properly insulated. Do the same insulation test with inductor 2, the copper electrode in jar 1, and the copper electrode in jar 2.
 
  • #3
Orthoceras said:
Test the insulation. Disconnect the wires. Charge a balloon by rubbing it against hair or wool. Connect the electroscope to inductor 1, and try to charge the inductor with the charged balloon. If the electroscope leafs do not rise, the inductor is not properly insulated. Do the same insulation test with inductor 2, the copper electrode in jar 1, and the copper electrode in jar 2.
Hi, thanks for your answer.
As I already explained in the post, the electroscope leafs do rise, but only if the containers aren't connected. I'm guessing that because of the coils in the containers, am I right ?
Also, it should work if the coils are submerged right ?
I do realise charges are escaping somewhere, but I'm not sure where...
 
  • #4
Silloky said:
As I already explained in the post, the electroscope leafs do rise, but only if the containers aren't connected. I'm guessing that because of the coils in the containers, am I right ?

Sorry, I did not really understand your test descriptions. What do you mean by "coil" (in "attaching a coil to the electroscope", "inside the jars are some copper coils" and "coil-activated containers"), by "waving" (in "waving the polystyrene on the coil") and by "it works"?

Anyways, your observation that the electroscope leafs do not rise when the containers are connected, means that the containers are not properly insulated.
 
  • #5
Orthoceras said:
Sorry, I did not really understand your test descriptions. What do you mean by "coil" (in "attaching a coil to the electroscope", "inside the jars are some copper coils" and "coil-activated containers"), by "waving" (in "waving the polystyrene on the coil") and by "it works"?

Anyways, your observation that the electroscope leafs do not rise when the containers are connected, means that the containers are not properly insulated.
1730636620782.jpeg

1730636648875.jpeg

These are the coils in the container jars I am talking about.

By electroscope coil and waving I man something like this : https://www.wikihow.com/images/thum...ke-an-Electroscope-Step-13-Version-3.jpg.webp

Hope this makes it clearer.
Thanks in advance for any tip !
 
  • #7
Silloky said:
it being due on Monday,
Do you have a balloon and a sweater to use as a backup plan?
 
  • #8
berkeman said:
Do you have a balloon and a sweater to use as a backup plan?
How about 2 turn tables and a microphone?
 
  • #9
WWGD said:
How about 2 turn tables and a microphone?
Okay, this is obviously a teaching moment. What in thee world are you saying, son? :smile:
 
  • #10

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