Re:copy machine electrons

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From: pauld@exploratorium.edu
Date: Mon Feb 14 2000 - 05:39:25 PST 

Message-Id: <200002141339.FAA19901@isaac.exploratorium.edu>
From: pauld@exploratorium.edu
Subject: Re:copy machine electrons
Date: Mon, 14 Feb 2000 13:39:25 GMT

Hi David

The electrons sprayed onto the drum in a copy machine come from PGE
of course ;-)

They used to use rabbit fur to generate a static charge. But these days they
transform the line voltage to a high voltage, and spray electrons off of high
voltage points onto the drum. When Light hits the drum (of selenium for
example.) the drum becomes a conductor (see Al Sefl's reply) this allows the
charge to leave the drum where light hits the drum. The toner with an opposite
charge sticks to the drum at places that retain charge, i.e. where it was dark.
So dark toner is deposited where there was darkness on the image of the page.

Paul D in Sweden

I'll follow up later with the distribution of colloids with height. It is
exponential, isn't everything?

> I have a few questions on how light reduces substances. When light turns
> silver halides black or purple I understand that the silver is reduced, but
> what is oxidized, the halide? Any other details of the chemistry of
> photography would be appreciated.
>
> Also when a copy machine plate is charged up by light, where are the
> electrons coming from?
>
> I also have a question for Paul Doherty. A few months ago he explained the
> distribution of colloids in a gravitational field. I only remember a few
> main points. I believe the distribution depends on the weight of colloids
> and their random 'Brownian' motion . I then lost him as soon as he said
> that the mathematics was easy. Paul, could you write down the 'easy' math?
> Thanks
> David Lauter
>
>
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