Electron microscopes use something similar to a light bulb to produce electrons. This is called the filament. The filament is a piece of wire and when electricity goes through it, not only is light given off, but also electrons. These electrons are focused by a series of magnets. The magnets are made magnetic by electricity and are called electromagnets. The electrons can be focused on the sample and when they hit the sample a signal is given off. A special type of detector acts like a tv camera and the image of the sample is displayed on a tv screen. By changing how the electrons are bent and how the beam of electrons strikes the sample, you can change the magnification and focus of the tv image.