Question

Which lens in an electron microscope is used to control and focus the beam of electrons.
(a) Convex lens
(b) Concave lens
(c) Electromagnetic lens
(d) None of the above

Answer 1

Hint: Glass lens like a concave and convex lens is used only in a light microscope. They cannot detect the beam of electrons. Electrons. An electron microscope can detect the beam of electrons.

Complete answer:
The source of illumination in an electron microscope is a beam of accelerated electrons. They use shaped magnetic fields for the electron-optical lens system. The beam of electrons cannot be focused on a normal glass lens like a concave and convex lens. They are used only in light microscopy. So, in an electron microscope, electromagnetic lenses are used.

Additional Information: - Resolving power of a light microscope is pretty low compared to that of an electron microscope. It cannot reveal very small objects and structures.
- Ultrastructure of biological and inorganic specimens like microorganism cells, biopsy samples, metals, and crystals are investigated by using an electron microscope.
- The first electron microscope was developed in 1931 with a resolution of 400X magnification.
- One of the main disadvantages of an electron microscope is, it requires a specimen of 100nm which is very challenging to take sections of 100nm from biological specimens.
- Types of electron microscopes: Transmission electron microscope, scanning electron microscope, Reflection electron microscope, and scanning tunneling electron microscope.
So, the correct answer is ‘Electromagnetic lens’.

Note: The first electron microscope was invented in 1931 by Erust Ruska and Max Knoll and the first electromagnetic lens was invented by Hans Busch in 1926. The electron microscope is very expensive and the samples should be viewed in a vacuum because the molecules scatter with air.