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In electron microscope a beam of electrons is focused by a circular electromagnet (magnetic condenser). When an electron beam passes through the object, the electrons get scattered producing an image in the built in fluorescent viewing screen. The wavelength of electrons employed is approximately 0.005 nm. Resolving power is about 0.01-0.02 nm.
There are two types of electron microscopes in general use: the Transmission electron microscope (TEM), which has many features in common with the light microscope, and the Scanning electron microscope (SEM). TEM can resolve particles 0.001 nm apart. Viruses, with diameters of 0.01–0.2 nm, can be easily resolved.
The SEM generally has a lower resolving power than the TEM; however, it is particularly useful for providing three-dimensional images of the surface of microscopic objects.
OTHER TYPES OF MICROSCOPES:
INTERFERENCE MICROSCOPE: It not only reveals cell organelles but also enables quantitative measurement of chemical constituents of the cells such as lipids, proteins, & nucleic acids.
POLARISATION MICROSCOPE: It enables the study of intracellular structures using differences in birefringence.