What is thermionic emissions?

Thermionic emission is the process by which electrons are emitted from a heated surface or material. When a material is heated to a high temperature, the thermal energy causes some of the electrons in the material to gain enough energy to overcome the attractive forces of the material's atoms or ions and escape into the surrounding space. This emission of electrons is known as thermionic emission. It is commonly observed in vacuum tubes and electron guns, where a heated cathode emits electrons that can be accelerated and used for various applications such as generating electrical currents or producing images on a screen.