Microscope

A microscope magnifies and resolves the image of an object that otherwise would be invisible to the naked eye, or whose detail could not be resolved using the unaided eye. These objects include such items as human skin, the eye of a fly, cells of a living organism, microorganisms such as bacteria, protozoa and viruses, individual molecules, and atoms.

Some of the above objects are large enough to be visible using the magnifying power of a light microscope. Examples include skin cells, parts of insects, and bacteria. Bacteria appear just as tiny objects. They are so small that they approach the detection limits of the light microscope. In order to make out details of microorganisms such as bacteria, and to be able to visualize viruses, much higher magnification is required.

All light moves as a wave. The wavelength of visible light is too large to resolve much bacterial detail. Viruses are invisible. An analogy would be to place a small pebble in the path of an oncoming wave at an oceanside beach. The wave will pass right over the pebble, as if the pebble were not there. However, if the same pebble is placed in a stream, where the waves are much smaller in size, the pebble can disrupt the wave's path.

The 'smaller wave' in microscopy is achieved by the use of electrons instead of visible light. The wavelength of an electron beam is extremely small. Thus, objects like bacteria and viruses can be visualized. Indeed, versions of microscopes that rely on electrical repulsion between surfaces can now visualize molecules, including the constituents of deoxyribonucleic acid (DNA).