The strength of the magnetic lens depends upon the current that flows through it. The lenses used in EM are magnetic coils capable of focusing the electron beam on the specimen and illuminating it. In the electron microscopes, a tungsten metal is heated with the help of a high voltage current, electrons form a continuous stream, which is used like a light beam.
When atoms of a metal are excited by the external heat energy, electrons started to fly off from the atom.
The resolution in Em depends on the wavelength of radiation, Smaller the radiation, greater will be the resolution.Įlectrons are referred to as subatomic particles orbit around the atomic nucleus. All electron microscopes use a coil of wire wrapped around the outside of a tube (commonly referred to as a solenoid) as an electromagnetic and/or electrostatic lenses. In 1931, a physicist and electrical engineer, Ernst Ruska, and Max Knoll discovered the first transmission electron microscope. Instead of glass lenses, EM uses shaped magnetic fields to form an electron-optical lens. Electron microscope a higher resolving power than light microscopes. These microscopes use electrons of up to 100,000 times shorter wavelength as compared to the visible light photons. It is used to study the structure of tissues, cells, organelles, and macromolecular complexes in detail and often used for quality control and failure analysis. Electron microscope is used to obtain high-resolution images of biological and non-biological specimens. An EM uses the same principles of an optical microscope but instead of photons or particles of light, it concentrates electrons, charged particles located on the outside of atoms, onto an object. 
An electron microscope is a microscope, which uses electron beams as a primary source of illumination.9 Reference Definition of Electron Microscope
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