Thermionic Emission – Definition, Working, Methods, Uses & Applications

Definition of Thermionic Emission?

What is Thermionic Emission?

The process or interaction by which free electrons are discharged from the outer layer of a metal when outside heat energy is applied is called thermionic emission.

Thermionic emission happens in metals that are warmed to an exceptionally high temperature. In other words, thermionic emission happens, when enormous measure of outside energy in the form of heat is provided to the free electrons in the metals.

Metals under normal temperature

At the point when a limited quantity of heat energy is applied to the metal, the valence electrons gain sufficient energy and break the holding with the parent atom. The valence electron, what breaks the holding with the parent atom, turns out to be free. This electron, what breaks the holding with the parent atom, is called as the free electron.

The free electrons in the metal have some kinetic energy. However, they need more energy to escape from the metal. The attractive force of the atomic nuclei goes against the free electrons, which attempt to escape from the metal.

Free electrons in the metal have less energy contrasted with the free electrons in vacuum. Hence, free electrons require additional energy from the external source to bounce into the vacuum.

Metals under high temperature

At the point when heat energy applied to the metal is expanded to a higher value, the free electrons gain sufficient energy and overcome the attractive force of the atomic nucleus, which holds the free electrons in the metal. The free electrons, which overcome the attractive force of the nuclei, break the holding with the metal and bounce into the vacuum.

The free electrons, which are gotten away from the outer layer of a metal when heat energy is provided, are called thermions. Thermionic emission process assumes a significant part in the activity of electronic gadgets or devices.

Thermionic emanation depends upon heat applied to the metal and work function of the metal

The quantity of free electrons escaped from the metal is depends upon how much heat applied to the metal and the work function of the metal.

Heat applied to the metal

On the off chance that enormous amount of heat is applied to the metal, huge number of free electrons acquires sufficient energy and breaks the holding with the metal. The free electron, what breaks the holding with the metal, bounces into the vacuum.

On the other hand, if less amount of heat is applied to the metal, less number of free electrons acquires sufficient energy and breaks the holding with the metal. The free electron, what breaks the holding with the metal will jumps into the vacuum.

Thus, the quantity of free electrons transmitted from the metal increases with increase in heat. Hence, the free electrons discharged from the outer layer of metals are directly proportional to the temperature of the metals.

The minimum temperature at which the metal beginnings emitting the free electrons is called threshold temperature.

If the temperature of the metal is below the threshold temperature, the metal doesn’t emit the free electrons. Then again, if the temperature of the metal is equivalent to the threshold temperature or more prominent than the threshold temperature, the metal emits the free electrons.

Work function of the metal

The amount of external heat energy required to remove the free electron from the metal is called work function or threshold energy. The work function of metals is measured in electron volts (eV).

Metals that have low work function will require less amount of heat energy to make the free electrons escape from the metal. Henceforth, the metals with low work function emit huge number of free electrons at high temperature.

Then again, metals that have high work function will require more amount of heat energyenergy to make the free electrons escape from the metal. Henceforth, the metals with high work function radiate less number of free electrons at high temperature.

Consequently, the emission of free electrons from the metal is inversely proportional to the work function of a metal.

Uses & Applications of thermionic emission

The parts, which are made by the course of thermionic emission are utilized in the electronic gadgets, for example, cathode ray tube, radio and so on.

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