The method employed by most modern office photocopiers is xerography-using electrostatic charges and heat to print the required image on paper.
The device uses light (hence the ‘photo’ in photocopier) to increase the electrical conductivity of certain substances. Selenium, which is usually a poor electrical conductor, is often used as it allows for the free flow of electrons in an electric current when light is incident upon it.
Inside the copier is a drum coated in a substance such as selenium. As light passes underneath the document to be copied, it imprints the image on the document onto the drum using negatively charged ink known as toner.
More electrons flow where the light reaches as they are not blocked by text or an image, and vice versa, altering the pattern of the ink on the drum.
A blank piece of paper with a positive charge attracts these negative ink particles back from the drum, which are then fused onto the paper with heat to produce a copy of the original document.