A photo copy machine has components such as a halogen lamp, photo sensitivedrum, toner or the ink drum, and conveyor belt. When you place the document you want tobe copied upside down on the glass and press the start button, an intense beam of lightscans across the document from top to bottom and this light then gets reflected and falls thephoto sensitive drum. This photo sensitive drum is a metal which is electrostatically chargedby a high voltage wire called a corona wire. It is a semiconductor so it has the property toact as an insulator in dark areas and when light falls on it, it conducts electricity.When a beam of light was scanned across the document, light will reflect the whiteareas, however printed letters being black do not reflect any light.
When the reflected lightfalls on the photo sensitive drum, the areas of the photo-conductor which was exposed tolight becomes conductive and gets discharged whereas the area of the drum which was notexposed to light remains negatively charged. When this photo sensitive drum rotates, itcarries an electrical shadow towards the toner. The toner is positively charged, so it sticksto the electrical shadow which is negatively charged and an inked image of the document isformed on the drum. Then a blank sheet of paper is feed up from the hopper, as it movesalong, the paper is given a strong electrical charge. The toner image is transferred from thesurface of the drum onto a piece of paper.
This paper then passes through two hot rollers.The heat and pressure from rulers permanently fuses the toner particles on the paper.On the other hand, a laser printer uses a computer output to program the intensityof a laser beam onto the selenium-coated drum. At first the selenium’s drum is positivelycharged, the laser gets signal from the computer then it hits down at different points and itbecomes negatively charged. In a tonner hopper, it has a powder in it which is like ink footpaper and this powder is positively charged.
When the drum goes near it, the powder is onlyattracted to the negative part of the drum and sticks to it, forming reverse words on thedrum. Now the paper is negatively charged. It has a stronger charge than the drum so whenthe drum with the powder on it touches the paper, the powder is transferred from the drumto the paper. The paper now has words on it.