Electron Emission

The passage of electrons from a metal into a gas or vacuum is called electron emission. The mechanism of electron emission is  classified into the followings:

(1)  Thermionic emission: When energy applied to the conductor to emit electrons is in the form of heat, the process is called thermionic emission.

(2)  Photoelectric emission: When the energy applied to the metal is in the form of light energy, the process of electron emission is known as photoelectric emission.

(3)  Secondary emission: If a fast moving electron collides with the surface of the metal then the emission of electrons takes place. This is known as secondary emission.

(4)  Field emission: If the electrons are emitted from the surface of metal by maintaining a certain amount of electrostatic field between the two plats of vacuum tube then emission is known as field emission.

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