Re: [Phys-L] Charge division on Spheres.

[Carl Mungan <mungan@usna.edu>]

> Photo of largest can in place before connections and lid placement
> http://s880.photobucket.com/user/betwys/media/Capacity%20of%20%20Right%20Cylinders/IMG_1933.jpg.html <http://s880.photobucket.com/user/betwys/media/Capacity%20of%20%20Right%20Cylinders/IMG_1933.jpg.html>


I’m afraid that’s a very tough geometry. The rims of the two ends of the can are quite close to the outer pot and will dominate the capacitance in a tricky fashion. If we try my simple model:

C = 2 pi epsilon0 LENGTH / ln(0.23/DIAM) + pi epsilon0 DIAM^2 / d

where d = diameter of steel pot - LENGTH

then you get answers that follow the linear trend of your measured values but are only about 65% of the measured values. Again, the small spacing between the rims and the pot is the likely culprit.

Do you have a deeper pot so you can put the can vertically instead of horizontally? Then I would expect much better agreement with my model above, replacing “diameter of steel pot” with “distance from bottom to top cover of pot”. You should be able to try this at least with your small pots.

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Carl E. Mungan, Professor of Physics  410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363 
mailto:mungan@usna.edu     http://usna.edu/Users/physics/mungan/