Thermionic emission is the emission of electrons from the surface of the metal when high thermal energy is applied to it.
This occurs when the applied thermal energy is overcome the work function of the metal.
Work Function: The minimum amount of energy required to emit the electron from the surface of the metal.
Reference Source:
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[4] What is Thermionic Emission ? – Thermionic Effect & Factors on which it depends – Electronics Coach. Electronics Coach. Published September 25, 2017. Accessed December 18, 2021. https://electronicscoach.com/thermionic-emission.html.