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These accelerated primary electrons are made to be incident on the sample through condensing lenses and scanning coil. Stream of electrons are produced by the electron gun and these primary electrons are accelerated by the grid and anode. These signals can be fed into CRO through video amplifier as shown. The electron detector (Scintillator) is used to collect the secondary electrons and can be converted into electrical signal. A magnetic condensing lens is used to condense the electron beam and a scanning coil is arranged in-between magnetic condensing lens and the sample. It consists of an electron gun to produce high energy electron beam. these secondary electrons are collected by a positive charged electron detector which in turn gives a 3- dimensional image of the sample. When the accelerated primary electrons strikes the sample, it produces secondary electrons. SEM is used to study the three dimensional image of the specimen. Scanning electron microscope is an improved model of an electron microscope. In the medical field it is used to study about the structure of virus, bacterial etc which are of smaller size. In industries it is used to study the structure of textile fibers, surface of metals, composition of paper, paints etc.ĭ. It is used in the study of the colloids.Ĭ. It is used to determine the complicated structure of the crystals.ī. It has a very wide area of applications (e.g) in biology, metallurgy, physics,Ī. The focal length of the microscopic system can be varied. It can produce magnification as high as 1, 00,000 times as that of the size of the object.ī. In order to make a permanent record of the image of the object, the final image can also be obtained on a photographic plate.Ī. Further the image can be magnified by the magnetic projector lens and the final image is obtained on the fluorescent screen. Thus the transmitted electron beam on the falling over the magnetic objective lens, resolves the structure of the object to form a magnified real image of the object. The electrons are transmitted more in the less dense region of the object and is transmitted less (i.e.,) absorbed by the denser region of the object. These electrons are made as parallel beam and are focused on to the object. The electron beam is made to pass through the center of the doughnut shaped magnetic condensing lens. Stream of electrons are produced and accelerated by the electron gun. The whole arrangement is kept inside a vacuum chamber to allow the passage of electron beam. Similar to the condensing lens, objective and eye piece in an optical microscope here three magnetic lenses are used. The electron microscope consists of an electron gun to produce the stream of electrons. The essential parts of an electron microscope are as shown in the figure and for comparison an optical microscope is also shown aside. Similarly the divergence of the electrons can also be made by adjusting the position of the holes in the iron cases. When the holes face each other, the magnetic field in space between the two coils focuses the electrons emerging out from the electron gun. In general, the magnetic lenses are made of two coils C 1 and C 2 enclosed inside the iron cases which have one hole as shown. Normally in electron microscope magnetic lenses are used for focusing. Here the focusing of electrons can be done either by magnetic lens or by electrostatic lens. Since the resolving power is inversely proportional to the wavelength, the electron microscope has high resolving power because of its shorter wavelength.Īn electron microscope is similar to that of an optical microscope. These microscopes are widely used in the field of engineering and medicine.Ī stream of electrons is passed through the object and the electron which carries the information about the object are focused by electric and magnetic fields. It is a type of microscope in which instead of light beam, a beam of electrons are used to form a large image of very small object.