why does thermionic emission take place from a metal surface only ?
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Cos inner electrons are bound by atoms on all sides.
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When metals are heated to a very high temperature, free electrons are emitted from the surface of the metal, this process is called thermionic emission. The free electrons in the metal have kinetic energy but they do not have enough energy to escape from the metal surface. Hence some amount of extra energy is required from the external source for the free electrons to jump into the vacuum. When heat energy of the metals is increased to a certain high value, free electrons gain enough energy to overcome the attractive forces of the atomic nuclei, break the bonding with the metal and escapes into the vacuum. Thermionic emission takes place from the surface of metal because its easy for the free electrons to escape from the metal surface then from inside the metal where the attractive force is more as compared to the metal surface.
Hope it will help you. Thanks.
Hope it will help you. Thanks.
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