There are essentially four important parts to an ordinary microscope:
- The source of light.
- The specimen.
- The lenses that makes the specimen seem bigger.
- The magnified image of the specimen that you see.
In an electron microscope, these four things are slightly different.
- The light source is replaced by a beam of very fast moving electrons.
- The specimen usually has to be specially prepared and held inside a vacuum chamber from which the air has been pumped out (because electrons do not travel very far in air).
- The lenses are replaced by a series of coil-shaped electromagnets through which the electron beam travels. In an ordinary microscope, the glass lenses bend (or refract) the light beams passing through them to produce magnification. In an electron microscope, the coils bend the electron beams the same way.
The image is formed as a photograph (called an electron micrograph) or as an image on a TV screen.