This unit of energy is commonly used in atomic and nuclear physics The work function (f0)  depends on the properties of the metal and the
nature of its surface The minimum energy required for the electron emission from the metal
surface can be supplied to the free electrons by any one of the following
physical processes:
(i)
Thermionic emission: By suitably heating, sufficient thermal energy
can be imparted to the free electrons to enable them to come out of the
metal Rationalised 2023-24
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(ii) Field emission: By applying a very strong electric field (of the order of
108 V m–1) to a metal, electrons can be pulled out of the metal, as in a
spark plug