Write and explain methods to obtain emission of electron from metal.
Write and explain methods to obtain emission of electron from metal.
From metal surface emission of electron can be obtained by following methods.
$(1)$Thermionic emission : When metals are heated (current is passed through filament of metal) electrons are given sufficient heat (thermal) energy, electrons escape from the metal such emission is called thermionic emission.
Example : From diode, triode or TV tube electrons are emitted by using thermionic emission.
$(2) $Field emission : When metal surface are applied electric field of $10^{8} \frac{\mathrm{V}}{\mathrm{m}}$, electron are emitted from it. Such emission is called field emission.
$(3) $Photoelectric emission : When on a clean metal surface incident radiation of proper frequency, electron are emitted from it. Such emission is called photoelectric emission.
Electrons emitted are called photoelectron.
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