How come the black powder in a photocopier only sticks to some of the paper?

In a photocopier, the black powder, or toner, only sticks to certain areas of the paper due to the electrostatic process involved in the copying. The photoconductive drum inside the copier is charged and then exposed to light, which creates a latent image of the document. The toner, which is also charged, is attracted to the areas of the drum that have been exposed to light (representing the image), while repelled by the areas that remain charged. When the paper passes through, the toner adheres only to the specific areas that correspond to the image, resulting in the final printed output.