Understanding Copy Machines: The Science Behind Positive and Negative Charges

  • Thread starter RuroumiKenshin
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But this is the main idea.In summary, the color of the original paper (black or white) does not determine the charge in a copy machine. A cylinder in the machine is positively charged and light is pointed towards it. Black color absorbs the light, while white color reflects it. The cylinder then becomes neutral in the places where light reached, and remains positively charged in the places corresponding to black areas on the original paper. Negatively charged ink is then applied to the cylinder and only attaches to the positively charged areas. When the cylinder is rolled over a white paper, the ink transfers and the paper is dried, creating a copy. This process is known as the photoelectric effect.
  • #1
RuroumiKenshin
Why is it that black sends a positive charge through a copy machine while white sends a negative charge? I presume it has something to do with the wave lengths?

If you don't know how a copy machine works, consult me. I have an unexplained obssession of learning about copy machines (and it is more like a craving).
 
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  • #2
Originally posted by MajinVegeta
I have an unexplained obssession of learning about copy machines (and it is more like a craving).

Maybe you have Asperger Syndrome? Nah... I'm just joking with you.

eNtRopY
 
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  • #3
Originally posted by MajinVegeta
Why is it that black sends a positive charge through a copy machine while white sends a negative charge? I presume it has something to do with the wave lengths?

If you don't know how a copy machine works, consult me. I have an unexplained obssession of learning about copy machines (and it is more like a craving).

It is not this way Majin.
It is not that the black or white makes the charge !
What actually happens (as far as i remmember) is that a certain cylinder gets positively charged (and it is made of a certain material).
Then light is pointed towards the paper so that it reflects on this cylinder, black color will absorb the light, while white color will reflect the light.
Therefore light will reach the cylinder only from places that where white.
Now due to the photoelectric effect, the positive charge that where on the cylinder will become neutral the places where light came (iow, the white places).
So the cylinder will be positively charged only in the places corresponsing to black places in the original paper.
Afterwards negatively charged ink will be put on the cylinder, it will only attach to the places that are positively charged on the cylinder (places where light didn't come, therefore correspond to black places).
Then cylinder slides over a white paper, the paper is dried, and comes out from the machine.

My information are rusty in my mind, so maybe i am wrong ..
 
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