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Re: capacitance of a disk

On Thu, 8 Feb 2001, Carl E. Mungan wrote:

So what is the capacitance of an isolated disk? Feel free to make
whatever simplifications or approximations you want and otherwise
change the problem to make it more tractable or meaningful. Carl

To at least first order accuracy we can take the result for the
absolute potential of a *uniformly charged* disk

V = Q/(2 pi epsilon_o R)

to approximate that of a charged *conducting* disk and find,
therefore, that

C ~= 2 pi epsilon_o R

A conducting disk should actually have a slightly lower absolute
potential so the correct answer will be somewhat larger; I would
think perhaps 10 to 20% larger.

This compares pretty nicely to that of a sphere which would have
about twice the capacitance for the same size since it has about
twice the area to pack charge onto.

John Mallinckrodt
Cal Poly Pomona