A certain minimum amount of energy is required to be
given  to an electron to pull it out from the surface of the metal This
minimum energy required by an electron to escape from the metal surface
is called the work function of the metal It is generally denoted by f0 and
measured in eV (electron volt) One electron volt is the energy gained by an
electron when it has been accelerated by  a  potential difference  of 1 volt, so
that  1 eV = 1