brimstone
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Could someone be so kind as to explain how a photocopier works with regards to static electricity? Book definitions are so confusing.

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Morbo
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You whack the paper on the glass. There is a photoconductive drum or belt below the glass, made of selenium, I believe (but I suppose any other semiconductor would work too...). This selenium is initially positively charged.

Then you shine a bright light through the glass onto the paper. The light reflected from the white/lighter areas of the paper falls on the drum, liberating electrons from the photoconductor, and neutralizing the charge. Black/darker areas on the paper do not reflect the light, and leave positively charged areas on the drum.

Then the drum rotates around past some toner, which is negatively charged. This is attracted to the positvely charged areas on the drum, which represent the darker areas on the original. The drum rotates around further, and rolls onto a positvely charged piece of paper. The negative toner is attracted off the drum again onto the positive copy paper.

Finally, the positive paper is heated and pressed through rollers to fuse the toner to the paper and form a copy.

I think.
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Jonatan
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(Original post by Worzo)
You whack the paper on the glass. There is a photoconductive drum or belt below the glass, made of selenium, I believe (but I suppose any other semiconductor would work too...). This selenium is initially positively charged.

Then you shine a bright light through the glass onto the paper. The light reflected from the white/lighter areas of the paper falls on the drum, liberating electrons from the photoconductor, and neutralising the charge. Black/darker areas on the paper do not reflect the light, and leave positively charged areas on the drum.

Then the drum rotates around past some toner, which is negatively charged. This is attracted to the positvely charged areas on the drum, which represent the darker areas on the original. The drum rotates around further, and rolls onto a positvely charged piece of paper. The negative toner is attracted off the drum again onto the positive copy paper.

Finally, the positive paper is heated and pressed through rollers to fuse the toner to the paper and form a copy.

I think.
That seems pretty accurate. Incidentally this is very similar to how a laser printer works. Just remove the paper and instead have a computer shine a laser beam onto the light-sensitive drum.

Also, the material of the drum is chosen based on a few criteria that doesn't necessarily require a semiconductor. Basically the material needs to be easily ionised, it must have a low work-function so that light can knock charge away from it, and it must not be a conductor ( if it was conducting the charge would distribute itself homogeneously across the drum ). One of my old laser printers used some sort of organic light-sensitive material.

Machines that handle colour using this mechanism sends the paper through several times using three different toners, tho many colour copy machines use a normal scanner and ink-jet printer as this is often cheaper.
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