Re: Influence machine

[msantos@etse.urv.es]

> Tom,
> > My question to the List is this:  What is an "influence machine"?
>         According to Pointig and Thomson, Influence machines are
> eletrostatic generators that use induction rather friction to generate
> "source of electrifaction." The most common example is the Wimshurst
> machine. X-ray's in this period were usually generated using induction coils
> because they can supply higher currents, but for what Rutherford was doing
> these were not needed.
>         I hope this helps.
>
> Gary
>
> Gary Karshner
 Sorry, but as far as I know, electrostatic induction is not
the basic process for generating charges on the Wimshurst machine.
The starting point seems to me to be the charging of any plate
of one of the discs by means of friction: recall there are
cupper filaments rubbering these metallic plates.
(this may not be the only way for a plate to get charged)

Indeed, (electrostatic) induction, by it self, does not
generate any net charge: it is only a redistribution of
the charges of a conductor. Locally there may be a net charge,
but globally the conductor is still neutral. You must recollect
the undesired charges elsewhere to get it charged.

There is still an induction process between opposite
plates of both discs. Without going into details, basically
I thing this has two effects: to multiply the net initial
charge and to give rise to fixed polarity (both discs rotate
in opposite sense).

Regards,
M.A. Santos