A photocopier works approximately in the following way. I
don't know which of the processes you have listed apply but I'm sure you can figure that
out.
The photocopier has a charged plate covered with a
photoconductive material. By photoconductive I mean a surface that loses charge when
exposed to light. The plate is first positively charged and kept in the dark. Now the
sheet of paper which has to be copied is placed above it and light passed through it.
The areas which have an image do not allow light to pass through while light passes
easily through the other areas.
The light passing through
the paper strikes the plate and these areas become conductive and give up their charge.
Now a negatively charged ink powder is spread over the plate and it is attracted to the
areas on which light did not fall and which did not became conductive. When a positively
charged paper is placed on the plate, the particles stick to the paper at locations
which had an image in the original document.
The paper with
the ink is then passed through heated rollers that fuse the ink and makes the image
permanent.
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