Elementary Idea of Electron Microscope

In optical microscope, the ray of light can be bent by a lens system. By placing the object and the lens system in such a way, we control the direction of the ray to get a magnified image of the object. Since as 'electron' carriers charge it is possible to change the direction of a electron beam by means of electric fields. This property is made use of in an electron microscope.

What is the advantage of using an electron microscope compared to an optical microscope?

An ordinary optical microscope uses the visible radiation of wavelength 6000 . but if we use an electron microscope, the electron acts as a wave and it corresponding wavelength is small.

As we already know the wavelength of an electron is

by suitably arranging 'V' (say 300 volts) the wavelength of the electron can be made to

As the resolving power of a microscope is inversely proportional to the wavelength of light, the smaller the wavelength, the larger the resolving power. Hence, the resolving power of an electron microscope is much more than an optical microscope.

Accelerating the electron through a high potential difference will still reduce the wavelength.

Construction

The electron beam emitted by a filament is accelerated through a large potential difference in an electron gun. The electron beam is subjected to a magnetic field created by an electromagnet.

This beam falls on the object. This beam passes through the object and enters again a magnetic field produced by an electromagnet, which diverges the rays to produce a magnified image of the object. The focusing can be done by adjusting the current in the coil of the electromagnet. The magnification of an electromagnet can be as high as 1,00,000. But it is most used only for scientific research as focusing of the beam is not as easy in the case of an optical microscope.