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Wednesday, 19 December 2018

Generation of Free Electron





As we have learnt before, electrons are bound to the  atom by some forces. In order to free an electron therefore , an external force or energy greater than the binding energy of the electron to the atom must be provided. Such energy can be obtained from various sources, e.g. heat energy, light energy, energy stored in electric or magnetic fields, kinetic energy of electric charges bombarding the surface, etc. The above methods of setting electron free are grouped into four, namely:

(i) Thermionic or primary emission
(ii) Photo electric emission
(iii) Cold cathode emission
(iv) Secondary emission

Thermionic emission: This is a method by which electrons are liberated (made free) by use of heat, directly of indirectly.

Photo electric emission: This is a method which employs light energy through dissimilar materials to liberate electrons.

Cold cathode emission: This is a method of obtaining free electrons which are emitted bu energy stored in electric fields or magnetic fields.

Secondary emission: This is a method of obtaining  free electrons through the use of kinetic energy, I.e. electric charges are made to bombard the surface of the metal electrode.


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