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on what principle is an electron microscope based?

on what principle is an electron microscope based?

Grade:8

1 Answers

Apoorva Arora IIT Roorkee
askIITians Faculty 181 Points
9 years ago
Although there are similarities in principle between the layout of optical and electron microscopes, in practice the two are very different. The conventional electron microscope requires that the electron beam be in avacuum, because electrons cannot ordinarily travel an appreciable distance in air at atmospheric pressure. The column of the electron microscope is evacuated by pumps, and the specimens and any other necessary apparatus are introduced into the vacuum by means of air locks. Unlike the optical microscope, in which thelensesare of fixed focus and the distance between specimen and objective lens is varied, the electron microscope hasvariable-focus lenses, and the distance between specimen and objective lens and the separation of the lenses remain constant. Themagnificationis determined mainly by the value of the current (for magnetic lenses) through the intermediate and projector lens coils. The image is focused by changing the current through the objective lens coil. Another difference is that the optical microscope is usually operated so that the image is a virtual one, while in the electron microscope the final image is invariably real and is visualized on a fluorescent screen or recorded for study on a photographic plate in traditional instruments or—more usually in today’s laboratory—on a digital imaging system.
Thanks and Regards
Apoorva Arora
IIT Roorkee
askIITians Faculty

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