Thermionic Emission refers to the emission of electrons in the presence of electric potential and temperature. Thermionic emission occurs when a negative charged electrode is heated. The heat energy agitates the atoms and the electrons leave the surface of the negatively charged material.
|A Vacuum Tube|
The rate of emission increases with the temperature. Thermionic current occurs if an anode which is positive with respect to the cathode is placed near the cathode.