Thermionic Emission


  • Promita Ghosh


thermionic, electron, emission


This article is about thermionic emission.

When the energy required for electron emission from a metal is supplied in the form of thermal energy the process of electron emission goes by the name thermionic emission.

The free electrons in a metal move in a potential field which can be approximated as shown in the graph of energy vs distance.

The maximum energy possessed by an electron at 0 K is called Fermi energy (EF). All the energy states below EF are filled up and all the states above it are empty. If E0 be the height of the surface potential energy barrier then E0 — EF is the minimum energy at 0 K that enables an electron to escape from the metal. This is known as the work function of the metal. If Φ be the


voltage equivalent of work function then eΦ = E0 — EF Obviously no electron emission is possible at 0 K. However if the temperature of metal is increased then some of the electrons may be excited to higher states having energy greater than E0 and can escape from the metal. Using Fermi-Dirac statistics it is possible to calculate the number of electrons which are incident on the metal surface per sec per unit area with energies exceeding E0. Thus one can derive an expression for thermionic emission current density (J)


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Fundamental principles of electronics — B.Ghosh.



How to Cite

P. . Ghosh, “Thermionic Emission”, TEMSJ, vol. 3, no. 2, pp. 82-83, Jul. 2021.