Uses of Charging

Photocopier:

  1. There is an aluminium drum that is covered with a layer of photoconductor, like silicon. This photoconductive becomes conductor when light falls on it, but is an insulator when in the dark.
  2. A postively charged, high voltage wire makes the surrounding air molecules positive. These molecules deposit positive charges on the drum surface in the dark, and induces negative charges beneath the photoconductive layer.
  3. A bright light shines on a paper with writing that needs to be copied. A lens produces an image of the writing on the drum. Where light falls on the drum, the photoconductive layer becomes conducting and conducts the positive charge through into the negatively charged aluminium beneath. The remaining positive charges forms the image of the writing.

    Photocopier

  4. Toner (a black powder) is negatively charged and sprinkled over the drum. The powder is attract to the positively charged writings.
  5. A fresh copier paper is first deposited with more positive charges than the drum.
  6. This paper is passed over the drum. The negatively charged toner powder is attracted to paper. The drum rotates as the paper moves, so that the writing is transferred to the paper.
  7. The paper is passed through a heater, where the heat melts the toner powder. The image of the writing becomes permanently fixed on the paper.

Precipitator:

  1. Dirty air passes over negatively charged wire.
  2. Dirt particles in air get negatively charged.
  3. Dirt particles pass in between positively charged plates.
  4. Dirt particles attracted to plates.
  5. Clean air leaves precipitator.

Precipitator