What is the process called where electrons are produced at the cathode?

• A. Thermionic emission
• B. Photoelectric emission
• C. Field emission
• D. Secondary emission

Answer: (A)

Thermionic emission is the process where electrons are produced at the cathode. When the cathode is heated, electrons gain thermal energy and some have enough energy to overcome the metal’s work function and escape into the vacuum. The emission rate rises with temperature and is described by the Richardson-Dushman relationship, which links current density to temperature and work function. This differs from other forms of emission: photoelectric emission requires light to eject electrons, field emission needs an extremely strong electric field to pull electrons out via tunneling, and secondary emission results from electrons bombarding the surface and ejecting additional electrons. So heating the cathode to release electrons corresponds to thermionic emission.