Re: Influence machine

[msantos@etse.urv.es]

Leigh Palmer wrote:
> The Wimshurst machine is a self-excited electrostatic generator
> in the operation of which friction (triboelectricity) plays no
> fundamental role. Like the Kelvin water dropper it is a

Why? could you be more explicit. I mean, I do not know
this symetry argument. How symetry makes friction
irrelevant?

> symmetric device. In principle it can be run with either
> polarity, the "choice" being a random one determined by the
> statistical fluctuation of charge on macroscopic objects. The

What is the nature of this fluctuations? I believe you mean
that plates may get charged from the surrounding air, which
always contains some charged ions.

> electrophorus (and some Van de Graaffs) is an induction machine
> in which the polarity may be determined by triboelectricity, but
> the sustained operation of which depends solely on induction.

I agree, altough it doesn't seems to me this device has
trivial explanation. I would like to show it to the students,
but I still don't know how to derive the charge distribution
that appears on the disks, or how does the effectivity depends
on the angle between the two opposite cupper brushes.
Any hint?

Regards,M.A.Santos
msantos@etse.urv.es
>