What is the term for electron emission from a heated cathode?

What is the term for electron emission from a heated cathode?

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

Answer: (B)

When a cathode is heated, electrons gain enough thermal energy to overcome the surface barrier (the work function) and escape into the vacuum. This is thermionic emission. The heating provides the energy, not photons or electric fields. Other ideas differ: field emission relies on a strong electric field that lowers the barrier and causes tunneling, not heating. Secondary emission occurs when incoming particles knock electrons out of the material, generating additional electrons as a result. Photoelectric emission requires light to supply the energy to eject electrons, not heat. So the term for electron emission from a heated cathode is thermionic emission.

When a cathode is heated, electrons gain enough thermal energy to overcome the surface barrier (the work function) and escape into the vacuum. This is thermionic emission. The heating provides the energy, not photons or electric fields.

Other ideas differ: field emission relies on a strong electric field that lowers the barrier and causes tunneling, not heating. Secondary emission occurs when incoming particles knock electrons out of the material, generating additional electrons as a result. Photoelectric emission requires light to supply the energy to eject electrons, not heat.

So the term for electron emission from a heated cathode is thermionic emission.