The term for electron emission from a heated cathode?

The term for electron emission from a heated cathode?

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

Answer: (C)

When a cathode is heated, the thermal energy given to the electrons allows some of them to reach or exceed the surface work function and escape into the vacuum. This process is thermionic emission. It’s the heating, not an external field or light, that drives the electrons out. Other emission types rely on different triggers: a strong electric field can pull electrons out through tunneling (field emission); energetic particles hitting the surface can knock out additional electrons (secondary emission); and photons delivering energy can eject electrons (photoelectric emission). The question specifically describes emission caused by heating, so thermionic emission is the correct term.

When a cathode is heated, the thermal energy given to the electrons allows some of them to reach or exceed the surface work function and escape into the vacuum. This process is thermionic emission. It’s the heating, not an external field or light, that drives the electrons out.

Other emission types rely on different triggers: a strong electric field can pull electrons out through tunneling (field emission); energetic particles hitting the surface can knock out additional electrons (secondary emission); and photons delivering energy can eject electrons (photoelectric emission). The question specifically describes emission caused by heating, so thermionic emission is the correct term.