Electron Emission

Description:

To remove an electron from a metal we have to provide energy equal to work function to the electron.

For providing this energy there are multiple techniques out of which the following three are most popular.

Thermal emission

To release the electron we supply it energy by heating up the metal. When metal is heated up the electron absorbs the thermal energy and its vibrations increase and its energy also increase which leads to emission of electron.

The electrons which discharge using thermal energy are known as thermions and this emission is known as thermal emission.

Field-emission

To release the electron we supply it energy by supplying it potential energy. When metal is placed in an electric field produced by strong positive and negative charges, the electrons gains potential energy and it is discharged from the metal. This is known as field-emission.

The electrons which discharge using field-emission are known as electrons only.

Photo-electric emission

When light which is an electromagnetic wave falls on a metal, the free electrons absorb this energy resulting in increase of energy of the electron, when the energy reaches the work function value, the electron is discharged from the metal. This is known as photoelectric emission.

The electrons which discharge using photo-electric emission are known as photoelectrons.