Though most people have used a copier at some point in their lives, many do not understand the principles that guide their function. The machines work by exploiting the laws that cause attraction between particles with opposing electrical charges. When duplicating a document, copiers first imbue a surface with a positive charge and expose that surface to the document a user wishes to copy.
The dark parts of the document – those with writing or images - block out the light, and the other parts of the document allow light through onto the positively charged surface. The parts of the surface that the light touches lose their positive charge. Next, the copier disperses a negatively charged substance over the surface, and because of the physical law that encourages positive and negatively charged objects to attract, the substance adheres to the surface.
Finally, paper is set upon the negatively charged substance and then given a positive charge, causing the negatively charged substance to stick to the paper. The copier then heats the paper, permanently fusing the substance to it and producing a copy of the document.