Laser Printers:

In this, positively charged rotating drum coated with selenium is scanned by a laser beam. The areas where the laser beam hits lose their charge & the remaining portions remain charged positively. These are the areas where the copy is to be black. A negatively charged powdered toner adheres to the positive areas of the drum which is transferred then to black paper to form the copy. In coloured printers, the procedure is repeated for each primary colour.