Introduction to Electronic Emission
As we have torch light in our homes.
It consists of a battery from which the electrons jump from a lower level to the higher energy level.
And when the electron returns back then it emits light So this the electron emission.
Let’s study the Introduction to electronic emission
Every metal has free electrons inside it.
Now these electrons require some amount of energy to come out of the metal surface.
And the energy required to come out of the metal surface is called the work function.
If we supply this energy from some external source then electrons will absorb energy and come out from the metal surface.
That means if we provide the energy to metal greater than its work function then the electrons will come out from the metal surface.
And this phenomenon is called as electronic emission.
Now let’s study the types of electronic emission.
When the metal is heated up and the moment of the heat energy is greater than the work function.
Then this thermal energy is absorbed by the electrons and electrons come out from the metal surface. such kind of emission is thermionic emission.
If a huge amount of electric field of range
is applied to the metal.
Then the energy of that field is absorbed by the electrons and electrons comes out from the metal surface. this emission is called as field emission.
However such method of field emission is very dangerous that's why it is least efficient.
Now we have a photosensitive metal plate on which the moment of light is exposed of a frequency which is greater than the threshold frequency of plate.
This light is considered to be having discrete energy packets which is photons and the energy
of photons is given by,
When this energy
is absorbed by electrons and if the
is greater than work function of the metal surface.
Then the electrons are emitted out of the metal surface. such kind of emission is called as photoelectric emission.
However, the rate of emission of electrons from such kind of emission is very less.
when we have fast moving electrons are made to collide to metal surface.
These fast moving electrons are absorbed by the free electrons inside the metal surface and these electrons come out of the metal surface.
Hence the electrons that come out from the metal surface are secondary electrons and emission due to it is called as the secondary emission.
The concept behind all these emissions is the energy inside the metal has to be greater than the work function of metal.
When we provide the energy to metal is greater than its work function then the electrons will come out from the metal surface. this called the electronic emission.
The thermionic emission, field emission, secondary emission and photosensitive emission are the types of electronic emission.