Essay Comparing The Light And Electron Microscope

Comparing the Light and Electron Microscope

In this essay I am going to be comparing the light and electron microscope, I will look at the advantages and disadvantages of each microscope and then analyse my findings to see if one is better than the other.

The light, or optical microscope as it is also known was invented in the 17th century, it has been refined in many ways over the years but it is essentially still the same. The light microscope works by; light rays from a light source beneath the stage are through to glass lenses in series. The two lenses are called the objective lens and the ocular (eyepiece) lens. Depending on their strength these two lenses on their own routinely provide

For the light microscope this distance is approximately 0.2µm. So in theory it might seem possible to magnify an object indefinitely by means of glass lenses in series. This has been put into practice and has only produced a larger and fuzzier picture; so the resolution is not improved and no more detail is visible. The resolution of the light microscope is imposed by the wavelength of visible light, and means that little is gained by magnifying an object more than 1500 times. This limits the amount of structural detail that can be seen within a cell. Higher magnification with good resolution can be obtained by using a special objective lens. This lens is called an Oil Immersion lens; this is a lens with fluid (oil) between the lens and the objective, but even with this lens it not possible to achieve effective magnification above 2000 times. The light microscope opened up a new world of structural detail for biologists, revealing the variety of cell forms making up new organisms. After a while scientists became curious, as the limitations prevented them

Whereas the light microscope uses glass lenses to focus the light rays, the electron beam of the electron microscope is focused by powerful electromagnets. The image produced by the electron microscope cannot be detected directly by the naked eye. The beam of electrons is directed on to a screen from which black and white photographs, called Photoelectron micrographs, can be taken. There are two main types of electron microscope. These are called the Transmission electron microscope (TEM), and the Scanning electron microscope (SEM). In the TEM, a beam of electrons is passed through thin, specially prepared slices of material. As the molecules in the air would absorb the electrons, a vacuum has to be created within the instrument. Where electrons are absorbed by the material, and do not therefore reach the screen, the image is dark. Such areas are said to be electron dense. Where electrons penetrate, the screen appears bright. These areas are termed electron transparent. As electrons have a very small mass,