A photon of energy 4 eV is incident on a metal surface whose work function is 2 eV. The minimum reverse potential to be applied for stopping the emission of electrons is

From Einstein's photoelectric equationEk=12mvmax2=hv−WWhere  Ek  is  maximum  kinetic  energy  of  electron,  v  is  frequency  and  W  is  work  function.⇒12mvmax2=4eV−2eV=2eVbut  12mvmax2=eVowhere  Vo  is  stopping  potential.Thus,  eVo=2eV⇒Vo=2V.