How does the laser printer operate?
The printing process starts with a green, light sensitive cylinder called the Drum. This Drum is charged with -700 volts. A laser beam then fires at the Drum and wherever it hits the drum it “shoots off” electrons, making the charge less. The Drum rotates and comes past the developer roller of the cartridge. This developer roller is a rubber roller with a tin layer of toner which is also charged at -700 volts. (partially by static electricity from friction, partially from the high voltage power supply) Wherever the Drum is still charged at -700 volts, there is no difference in potential and there is no electrostatic attraction. Wherever the Drum is charged less than -700 volts, toner particles (which is basically plastic dust) will be attracted to the drum. The lower the charge that is left on the drum, the more toner is attracted and the darker the color will be. This is also the reason laser jet printers are not very good at printing very light colors, it’s like picking up one paper
