Question

$\left(i\right)$ What is thermionic emission?
$\left(ii\right)$ Name the unit in which the work function of a metal is expressed.

Answer 1

$\left(i\right)$ The emission of electrons from a metal surface when heat (or thermal) energy is imparted to it is called thermionic emission.
$\left(ii\right)$ The work function of a metal is expressed in the the unit $eV$ (electron volt)

$1eV=1.6\times {10}^{-19}J$.