Thermionic emission is a process of emission of charge particle (known as thermion) from the surface of a heated metal.
The charge particles normally are electrons.
The rate of emission (number of electrons emitted in 1 second) is affected by 4 factors, namely
the temperature of the heated metal,
When the temperature of the metal increase, the emission rate of electron will increase.
the surface area of the heated metal,
When the surface area of the metal increase, the emission rate of electron will increase.
the types of metal
The rates of thermionic emission are different with regard to different types of metals.
the coated material on the surface of the metal.
If the surface is coated by a layer of barium oxide or strontium oxide, the rate of emission will become higher.
Thermionic Diode
Thermionic emission is applied in thermionic diode.
A diode is an electrical component that only allowed current flows in one direction.
Figure below shows the illustration of a thermionic diode.
Electrons can only released from the tungsten filament (when it is hot) and move toward the anode which is connected to the positive terminal.
Electrons are not allowed to move in the opposite direction because no electrons will be released from the anode.
As such, the electrons can only move from left to right but not the other way round.
