Ending a lab on static electricity I added a question that required
students to look up how a photocopier worked. Knowing that it worked on
static electricity principals (and many others). I thought it would be a
good experience for them to see a practical application. I fully
expected differing sites to say the paper (or drum depending on the
style of photocopier) was positive and in other sites to say that it was
negative. The sites that didn't say the toner was positive (or negative)
didn't say anything about the toner being neutral and then polarized
either. When I started grading the reports I was surprised to see many
students saying that the toner was also charged. When I assigned the
question I was trying to get the students to see an application of
neutral objects being polarized by a charged particle. In the case of
photocopiers the toner getting polarized and sticking to the parts of
the paper that were charged positive (or negative). I did a Google
search and checked a number of websites yesterday and many of them
stated that the toner was charged opposite the paper (either positive or
negative depending on the style of machine). This was astounding to me.
I would expect that if the toner was all charged negative for example
that it would be very difficult to get it into the copier - the fine
toner would be repelled by the same charge toner already there and would
make a mess. I was counting on the toner being neutral and being
attracted because of polarization. There was one site that even
described the negative toner being attracted to the paper like pepper
being attracted to a charged balloon. We just did this in the experiment
but the pepper did not have a charge that I could tell. It certainly
wasn't repelled from the positive glass rod or repelled from the
negative balloon. Does anyone have direct experience with this? Is the
toner in a real copy machine charged before it is applied to the paper?
I'm quite convinced that it is not charged in the toner containers that
are put into the machine.
--
Arlyn DeBruyckere
Science Teacher
School Photographer
Hutchinson High School
1200 Roberts Road SW
Hutchinson MN 55350