Quick Electron Emissions:

Quick electron emissions refer to the rapid emission of electrons from a material. This process occurs when a material releases electrons due to the application of external stimuli such as light, electric fields, or heat. Among the given options, field emission is the only process that involves quick electron emissions. Let's discuss each option in detail to understand why field emission is the correct answer.

a) Photoelectric emission:
- Photoelectric emission is the phenomenon in which electrons are emitted from a material when it is illuminated with light of appropriate frequency or energy.
- The process involves the absorption of photons by the material, which excites the electrons to a higher energy level.
- If the energy of the absorbed photons is greater than the work function of the material, the excess energy is converted into the kinetic energy of the emitted electrons.
- However, photoelectric emission is not considered a quick electron emission process as it requires the absorption of photons, which may take some time.

b) Field emission:
- Field emission is the process in which electrons are emitted from a material due to the presence of a strong electric field.
- This emission occurs when the electric field at the surface of the material is strong enough to overcome the work function barrier.
- The electrons are accelerated by the electric field and emitted into vacuum or a low-pressure gas environment.
- Field emission is a quick electron emission process as it does not require any external stimulation such as light or heat. The emission occurs almost instantaneously when the electric field is applied.

c) Secondary emission:
- Secondary emission refers to the emission of electrons from a material due to the impact of high-energy electrons or ions.
- When a high-energy electron or ion strikes the surface of a material, it can dislodge additional electrons from the material.
- However, secondary emission is not considered a quick electron emission process as it requires the initial impact of high-energy particles to trigger the emission.

d) Thermionic emission:
- Thermionic emission is the process in which electrons are emitted from a heated material.
- When the material is heated to a sufficiently high temperature, the thermal energy can excite the electrons to overcome the work function barrier and escape from the material.
- Thermionic emission is not considered a quick electron emission process as it requires the material to be heated to a specific temperature.

In conclusion, among the given options, field emission is the only process that involves quick electron emissions. It occurs when a strong electric field is applied to a material, causing the rapid emission of electrons.